Clinical Gait Analysis Book 2024-2025 PDF

0 BIOMECHANICS I GAIT ANALYSIS DR. AYA KHALIL Lecturer of Biomechanics, Kinesiology & Ergonomics 2024/2025  HORUS UNIVERSITY – EGYPT FACULTY OF PHYSICAL THERAPY QUALITY...

0 BIOMECHANICS I GAIT ANALYSIS DR. AYA KHALIL Lecturer of Biomechanics, Kinesiology & Ergonomics 2024/2025  HORUS UNIVERSITY – EGYPT FACULTY OF PHYSICAL THERAPY QUALITY ASSURANCE UNIT Vision The Faculty of Physical Therapy at Horus University strives to be a local and regional competitor in educational programs, distinguished by scientific research that supports sustainable development and community service. Mission The aim of the faculty of Physical Therapy at Horus University is to prepare competent graduates in the field of physical therapy, capable of providing high-quality competitive healthcare through the provision of an excellent academic environment and advanced educational programs that encourage self-learning, continuous learning, and systematic scientific research; thereby contributing to development and solving societal problems. Strategic Goals 1. Improving institutional performance efficiency to ensure quality performance. 2. Achieving excellence in the educational program and enhancing graduate competitiveness. 3. Enhancing the scientific research system and supporting excellence and innovation. 4. Providing exceptional community services and contributing to environmental development for sustainable development. 5. Qualifying the faculty for accreditation according to the standards of the National Authority for Quality Assurance and Accreditation in Education.  ‫جامعة حورس‪ -‬مص‬ ‫كلية العالج الطبيع‬ ‫وحدة ضمان الجودة‬ ‫رؤية الكلية‬ ‫ً ى‬ ‫ً‬ ‫ً‬ ‫البامج‬ ‫تسع كلية العالج الطبيع ‪ -‬جامعة حورس أن تكون منافسا محليا وإقليميا ف ر‬ ‫ى‬ ‫متمبة بالبحوث العلمية الداعمة للتنمية المستدامة وخدمة المجتمع‪.‬‬ ‫التعليمية‪،‬‬ ‫رسالة الكلية‬ ‫ى‬ ‫ى‬ ‫خريجي أكفاء ف مجاالت العالج‬ ‫تهدف كلية العالج الطبيع جامعة حورس إىل إعداد‬ ‫الطبيع‪ ،‬قادرين عىل تقديم رعاية صحية تنافسية عالية الجودة من خالل توفب بيئة أكاديمية‬ ‫متمبة‪ ،‬وبرامج تعليمية متطورة‪ ،‬تشجع عىل التعلم الذات والمستمر‪ ،‬والبحث العلم‬ ‫ى‬ ‫المنهج؛ بما يساهم ىف التنمية وحل مشكالت المجتمع‪.‬‬ ‫ر‬ ‫األهداف االسباتيجية‬ ‫‪.1‬رفع كفاءة االداء المؤسىس لضمان جودة األداء‪.‬‬ ‫ى ى‬ ‫البنامج التعليم ورفع القدرة التنافسية للخري ج‬ ‫التمب ف ر‬ ‫‪.2‬تحقيق‬ ‫ى‬ ‫التمب واالبتكار‬ ‫‪.3‬تعزيز منظومة البحث العلم ودعم‬ ‫ى‬ ‫متمبة وتنمية البيئة لتحقيق التنمية المستدامة‬ ‫‪.4‬تقديم خدمات مجتمعية‬ ‫‪.5‬تأهيل الكلية لالعتماد طبقا لمعايب الهيئة القومية لضمان جودة التعليم‬ ‫واالعتماد‪.‬‬ Contents Biomechanics 1 Mobility assessment 7 Analysis of movement 8 Gait cycle 10 Gait analysis: Temporospatial descriptors of the gait 18 Running gait 22 Sagittal plane kinematics across joints for each phase of the gait cycle 26 Center of mass displacement 31 Kinematic strategies to optimize energy expenditure during gait 33 Instrumentations for gait analysis (Temporospatial parameters) 40 Instrumentations for gait analysis (Angular displacement) 42 Kinetic gait analysis 47 Center of Pressure 53 Instrumentation for gait analysis (Ground reaction force, muscle myoelectrical activity and plantar pressure) 56 Clinical Evaluation of Gait Disorders 64 Developmental biomechanics in gait analysis 66 Pathological Gait: Observational gait analysis 73 Major deviations and impairments: Ankle, foot, and toes 79 Major deviations and impairments: Knee 86 Major deviations and impairments: Thigh 90 Major deviations and impairments: Pelvis and trunk 93  Biomechanics The origin of the word Direct translation from Greek is “the study of living machines "bio" means "life" and "mechanics" means "the study of machines". Definition The study of the forces that act on a body and the effects they produce. Biomechanics is the intersection of biology, physiology, anatomy, physics, mathematics, and chemistry to solve difficult problems in medicine and health. Biomechanics is the application of physics and mathematics on biological problems. Mechanics is divisible into two disciplines: statics and dynamics. Statics is defined as the study of systems in a constant state of motion (including no motion). Dynamics is defined as the study of systems in motion. They can be further subdivided into kinetics and kinematics. Kinetics is the study of forces and kinematics the study of time and space. Schematic of the basic concepts in biomechanics. 1  Disciplines intersection in biomechanics Bio Mechanics Anatomy physiology Mathematics and physics Planes (Sagittal) Action potential Newtons law Movement (flexion) Mechanism of muscle Friction Muscles (Quadriceps) contraction Arteries Anatomical positions Basic mechanics considerations The mechanical terms and principles necessary for efficient movement analysis. Kinematics Linear kinematics Distance Speed (velocity) Angular kinematics Angle Angular displacement Kinetics Linear kinetics Newton laws of motion o Action reaction—law of reaction (Newton’s third law): To every action there is a reaction, which is equal in magnitude and opposite in direction. The force platform is used to measure the ground reaction forces which are created from our exertion of forces against the ground during walking or running. Friction Work Power Angular kinetics Torque or moment of force Joint torque Equilibrium (Stable & Dynamic) Center of gravity 2  Posture control 1. The human’s base of support (BoS) is the area bounded posteriorly by the tips of the heels and anteriorly by a line joining the tips of the toes. 2. The human’s center of gravity (CoG) is the point where the mass of the body is centered. It is located just anterior to the body of the second sacral vertebra. 3. The line of gravity is the line of force passing vertically downwards from the center of gravity and remains within the area on the ground which is supporting it. 4. The normal sway of the body during quiet MA standing moves the center of mass and the center of pressure of the body anteriorly and posteriorly up to 7 mm. 5. Center of pressure locates the center of the distributed pressures under both feet. The CoP measurement has been used to imply the relative position of the ground reaction force vector (GRFV). Location of the ground reaction 6. When the body contacts with the ground, force vector (GRFV) and the line there is an equal and opposing force of gravity (LoG) in the optimal standing posture. generated. The force produced by the ground in stance or during gait is called the ground reaction force (GRF). This force has three directional components corresponding to each of the cardinal planes. 7. In quiet stance, the GRFV and the LoG have coincident action lines that create equal and opposite external forces on the joints of the human body. The internal and external moment The influence of the internal and external forces acting on the body segments during standing is determined by the location of the LoG in relation to the joint axis of rotation. 1. When the LoG passes directly through a joint, no moment is created. 2. If the LoG passes at a distance from the axis of rotation, an external moment is created. 3  a. Rotation of that joint will occur unless it is opposed by an internal moment created by passive tissue tension or muscle contraction. b. The magnitude of the external or internal moment is dependent upon the magnitude of the applied force and the moment arm. c. The moment arm (MA) is the perpendicular distance between the joint axis of rotation and the applied force vector. The moment arm of the ankle joint is the largest and it is 4 to 6 cm anterior to the ankle joint. Alignment in the Sagittal Plane in Standing Posture JOINTS LINE OF EXTERNAL PASSIVE OPPOSING ACTIVE OPPOSING GRAVITY MOMENT FORCES FORCES Atlanto-occipital Anterior Flexion Ligamentum nuchae and Posterior neck muscles alar ligament; the tectorial, atlantoaxial, and posterior atlanto- occipital membranes Cervical Posterior Extension Anterior longitudinal ligament, anterior anulus fibrosus fibers, and zygapophyseal joint capsules Thoracic Anterior Flexion Posterior longitudinal, Back extensors supraspinous, and interspinous ligaments Zygapophyseal joint capsules and posterior anulus fibrosus fibers Lumbar Posterior Extension Anterior longitudinal and iliolumbar ligaments, anterior fibers of the anulus fibrosus, and zygapophyseal joint capsules Sacroiliac joint Anterior Nutation Sacrotuberous, sacrospinous, iliolumbar, and anterior sacroiliac ligaments Hip joint Posterior Extension Iliofemoral ligament Ilipsoas Knee joint Anterior Extension Posterior joint capsule Ankle joint Anterior Dorsiflexion Soleus, gastrocnemius 4  Areas of biomechanics Developmental biomechanics Biomechanical research in human development focuses on evaluating essential movement patterns across the human life span. Biomechanical analysis is specifically important in quantifying the development of motor skills and movement patterns such as walking, kicking, jumping, throwing, and catching. Biomechanists have used high-speed camera systems and force platforms to capture and analyze slight movement changes in young children. The data from these devices have assisted biomechanists in objectively examining movements such as body sway during sitting and standing, and/or the range of motion at the joints during walking. Recently the American Physical Therapy Association recognized walking speed as the sixth vital sign of overall health. In addition, biomechanists develop biomedical devices that can improve the quality of life for older adults and prevent injury such as the ankle exoskeleton. Exercise biomechanics In the area of exercise, biomechanical research has focused on postures and movement patterns that minimize the risk of injury during physical activity and improve performance. The best example are the development of exercise machines for improving strength, endurance, flexibility, and speed, the development of new exercise modes, such as plyometrics and isokinetics, to improve performance; the design of exercise and sports equipment to minimize injuries, and the development of exercise and sport techniques to optimize performance. Rehabilitative biomechanics It involves studying the movement patterns of people with injury or disability. Biomechanists analyze movement changes after injury and determine the specific movement abnormality. This information is crucial for clinicians, especially physical therapists and athletic trainers, when developing an appropriate rehabilitation protocol for individuals to relearn motor skills after an injury. An example of rehabilitative biomechanics is the development of assistive devices such as canes, crutches, walkers, and orthotics; and the 5 development of rehabilitative devices such as prostheses and wheelchairs. By using objective biomechanical measurements obtained through equipment such as goniometers, handheld dynamometers, and force transducers, biomechanists can determine the effectiveness of those assistive and rehabilitative devices and provide professional opinion to help physicians and therapists improve their usage. Occupational biomechanics Biomechanical research often focuses on providing a safer environment for the worker (Ergonomics). The development of better safety equipment (e.g., helmets, shin guards, and footwear) to protect the body from impacts and collisions with objects is an important area of biomechanical research. In addition, the development of safer or more mechanically efficient tools, improvements in the designs of transportation modules, and the decrease in occupational injury have involved major contributions by biomechanists to various work environments (work-related muscloskeletal injuries). Biomechanists are involved in legal cases involving industrial design and safety. To reduce the incidence of occupational injury, biomechanists objectively evaluate working performance and develop optimal environments. For example, biomechanists have examined proficiency in robotic assistive surgery by measuring the joint range of motion and the muscle activation of the surgeons’ upper extremities during surgical procedures. Forensic biomechanics Biomechanical research in this area is related to questions that arise in legal situations. Forensic biomechanists are invited to analyze evidence, clarify some of the most important issues, and facilitate the decisions of the jury. A quick look into the future of biomechanics, biomechanics will influence many professional domains in order to understand fundamental movement in sports, exercise, medicine, robotics, biology, gaming, and occupational science. Human movement will also be studied to a greater extent using virtual reality that is portable and easy to use. The use of virtual reality takes biomechanical research beyond the laboratory settings to simulating actual 6 environments from which natural human movement responses can be detected. Mobility assessment Mobility is the ability to move one’s body through space. While walking may be considered the most common manifestation of mobility, mobility capacity can be considered to range from rolling over in bed to running a marathon or walking a tightrope. Indicators of mobility capacity can be obtained from self-report, professional assessment or observed performance. self-report measures of mobility are common and often include items related to transfers, walking ability and stair climbing. Self-report measures represent the perspective of the person. However, when multiple items about mobility are combined in a scale that is based on degree of difficulty for each item, it can be difficult to interpret a summary score. Gait Gait can be defined as any method of locomotion characterized by periods of loading and unloading of the limbs. This includes running, hopping, skipping, swimming, and cycling. Walking is the most frequently used gait, providing independence, and used for many of the activities of daily living (ADLs). It also facilitates many social activities and is required in many occupations. Walking (ambulation) 1. serves an individual’s basic need to move from place to place and is therefore one of the most common activities that people do daily. Ideally, walking is performed both efficiently, to minimize fatigue, and safely, to prevent falls and associated injuries. 2. Habitual bipedal locomotion requires the central nervous system to generate appropriate motor actions from the integration of visual, proprioceptive, and vestibular sensory inputs. 3. Translatory progression of the body, produced by coordinated, rotatory movements of body segments. The alternating movements of the lower extremities essentially support and carry along the head, arms, and trunk, which constitute about 75% of total body weight, with the head and arms contributing about 25% of total body weight and the trunk contributing the remaining 50%. 7  4. Serves as a locomotive mechanism. It is defined as a series of movements of the lower extremities in such a rhythmic motion that result in the forward progression of the body with minimal energy expenditure. The prerequisites of normal gait are: Stability and posture, Range of motion (ROM), Muscle strength, Co- ordinated motor control, Muscle tone, Proprioception, Vision, Cognition, Aerobic capacity. Five main tasks for walking gait: 1. Maintenance of support of the head, arms, and trunk, that is, preventing collapse of the lower limb 2. Maintenance of upright posture and balance of the body 3. Control of the foot trajectory to achieve safe ground clearance and a gentle heel or toe landing 4. Generation of mechanical energy to maintain the present forward velocity or to increase the forward velocity 5. Absorption of mechanical energy for shock absorption and stability or to decrease the forward velocity of the body. Analysis of movement Human motion analysis is the systematic study of human motion by careful observation augmented by instrumentation for measuring body movements, body mechanics and the activity of the muscles. It aims to gather quantitative information about the mechanics of the musculoskeletal system during the execution of a motor task. A special branch of human motion analysis is gait analysis, which is specific to the study of human walking, and is used to assess, plan and treat individuals with conditions affecting their ability to walk. Applications of human motion analysis Human motion analysis is a useful investigative and diagnostic tool in many research and clinical areas, such as medicine, ergonomics and sports. Through human motion analysis, the deviations from normal movement in terms of the altered kinematic, kinetic or EMG patterns 8  can be identified and then used to evaluate the neuromusculoskeletal conditions, to help with subsequent treatment planning and/or to assess the efficacy of treatment in various patient groups, such as those with Cerebral Palsy, stroke, knee osteoarthritis (OA), diabetes mellitus (DM) and spinal cord injury (SCI). Human motion analysis has also seen many applications in assistive technology, such as prosthetics and orthotics, in which accurate evaluation of critical joint motion characteristics can be obtained from human motion measurements. In sports science and medicine, human motion analysis is also widely used to help optimize athletic performance and to identify mechanisms of common sports injuries and the accompanied posture-related or movement-related problems. Based on gait analysis results, the evaluation of the pathological condition, surgical planning and the development of treatment regimes. It can alter recommendations for surgical intervention and ultimately reduce the amount of surgery. Analysis of movement can be performed qualitatively or quantitatively. Analysis of movement types Item qualitative quantitative Performance Performed daily Precise Based on Biology (anatomy & mechanics knowledge of physiology) example Description (i.e., good, bad, Numbers (i.e., 5 meters, 4 long, heavy). seconds, 11 kg) Description nonnumeric analysis numerical Instrumentation Requires no Requires instrumentation Gait analysis The scientific investigation of human locomotion. It includes recording and interpreting biomechanical measurements of gait to understand the effects of disease and dysfunction that contribute to disability during locomotion. 9 It is a specialized medical technology used to evaluate patients with complex walking problems such as children with cerebral palsy (CP). It is a systematic way of identifying any variations in the gait pattern and trying to find out the reasons associated with it and how they can affect the human. Reasons for performing gait analysis Determine of gait functionalities, irregularities, and classifications. Select of better treatment for patients Provide gait enhancement facilities. Monitor the progress and predict the outcome of an intervention. Evaluate the effect of various rehabilitation interventions To better perform gait analysis, we will start with the definition and description of the gait cycle (GC) and its phases. Gait cycle Normal gait can be defined as a series of rhythmic, systematic, and coordinated movements of the limbs and trunk that results in the forward advancement of the body’s centre of mass. The fundamental unit of walking is a gait cycle. It’s usual to start the cycle (0%) with the first contact (initial contact, often called heel contact in normal gait) of one foot, so that the end of the cycle (100%) occurs with the next contact of the same (ipsilateral) foot, which will be the initial contact of the next cycle. A gait cycle consists of two main phases, stance, and swing, which are further divided into five and three functional phases, respectively. The stance phase corresponds to the duration between heel strike and toe-off of the same foot, constituting approximately 62% of the gait cycle. The swing phase begins with toe-off and ends with heel contact of the same foot and occupies 38% of the cycle. It is characterized by stance stability; toe 10  clearance during the swing; pre-positioning at swing; sufficient step length; as well as mechanical and metabolic efficiency. A stride (synonymous with a gait cycle) is the sequence of events taking place between successive heel contacts of the same foot. Stance is the entire period the limb is in contact with the ground and swing begins when the foot comes off the ground. Since there are two lower limbs, the events on the opposite (contralateral) limb are offset by 50%, so contralateral initial contact occurs at 50% cycle. When one limb is in swing phase, the other is in stance. Gait cycle (stride)= Rt step + Lt step Gait Cycle (GC) Period stance swing Wight Task acceptance Single limb support Limb advancement Initial Loading Mid Terminal Pre- Initial Mid Terminal Phases contact response stance stance swing swing swing swing % GC 0-2% 2-12% 12-31% 31-50% 50-62% 62-75% 75-87% 87-100% Foot Terminal Initial double Single stance (contralateral Single stance double contact stance stance limb) 11 12 Subphases of the stance and swing phases Stance Initial contact ( heel strike) This phase includes the The limb is positioned moment when the heel to start stance with a 0-2% just touches the floor heel rocker. Interval Definition Objectives Stance Loading response (Foot flat) It is the first instant Shock absorption during stance when the foot is flat Weight-bearing stability 2-12% on the ground. Preservation of progression Weight is rapidly transferred onto the outs tretched limb, the first period of double-limb support. Interval Definition Objectives 13  Stance Mid stance The point at which the body weight is directly over the supporting lower Progression over the stationary foot 12-31% Limb and trunk stability extremity. The body progresses over a single, stable limb. Interval Definition Objectives Stance Terminal stance (heel- off) The point at which the heel of the Progression of the body reference extremity leaves the 31-50% ground.The body moves ahead of beyond the supporting the limb and weight is transferred foot onto the forefoot. Interval Definition Objectives 14  Stance Pre-swing (push- off) It begins with heel-off and ends with toe-off of the gait cycle. It is characterized by large Position the limb 50-62% propulsive forces that propel the body forward for swing through swing phase and into the next gait cycle, the 2nd period of double limb support. Interval Definition Objectives Swing Intial swing (Toe-off) A rapid unloading of the limb occurs as weight is Foot clearance of the floor 62-75% transferred to the contralateral limbIt begins once the toe leaves the ground and continues Advancement of the limb until midswing, or the point at which the from its trailing position swinging extremity is directly under the body Interval Definition Objectives 15  Swing Mid swing It occurs approximately when Limb advancement 75-87% the extremity passes directly Foot clearance from the beneath the body floor Interval Definition Objectives Swing Late/Terminal swing The knee extends; the limb prepares to contact the ground Complete limb advancement 87-100 % for Initial Contact. Prepare the limb for stance Interval Definition Objectives 16 Stance is subdivided into three intervals according to the sequence of floor contact by the two feet: 1. Initial double stance (Double limb support): It begins the gait cycle. It is the time both feet are on the floor after initial contact. 2. Single stance (Single limb support): It begins when the opposite foot is lifted for swing. The duration of a single stance is the best index of the limb's support capability. 3. Terminal double stance: It begins with floor contact by the other foot (contralateral initial contact) and continues until the original stance limb is lifted for swing (ipsilateral toe-off). When double stance is omitted, the person has entered the running mode of locomotion (see next section about relationship between gait parameters and velocity of walking. 17  Kinematic and kinetic gait analysis Temporospatial descriptors of the gait DISTANCE (SPATIAL) CHARACTERISTICS Parameter Definition Average Values Stride length The linear distance between ground 1.42m contact of one foot (Rt IC) and to (Men: 1.51 the next ground contact of the same m; Women: foot (Rt IC) (two step lengths) 1.32 m) Step length The linear distance between ground 0.71 m contact of one foot (Rt IC) and to the next ground contact of the opposite foot (Lt IC) Step width (also The perpendicular distance between 7 to 9 cm known as base of similar points on both feet measured support) during two consecutive steps Foot progression Angle between the long axis of the 5 to 7 angle foot and the line of forward degrees progression Toe Clearance The minimal linear distance from 1.28 cm at the hallux to the floor during swing 80 % of GC phase 18  TEMPORAL (TIME) CHARACTERISTICS Parameter Definition Range of Values Average Reported in the Literature Female Male Stride time The time in / / 1 sec seconds from ground contact of one foot (Rt IC) and to the next ground contact of the same foot (Rt IC) (two step lengths) Step time The time in second / / / from ground contact of one foot (Rt IC) and to the next ground contact of the opposite foot (Lt IC) Speed (also Speed (also known 78 m/min 82 m/min / known as as velocity) The or or velocity) distance traversed 1.30 1.37 during a specified m/sec m/sec time (m/sec or m/min) Cadence Steps per minute 118 108 / steps/min steps/min Time in seconds / / 0.62 sec Stance time that the reference foot is on the ground during a gait cycle Swing time Time in seconds / / 0.38 sec that the reference foot is off the ground during a gait cycle 19  TEMPORAL (TIME) CHARACTERISTICS Swing/stance Ratio between the / / 0.63– ratio swing time and the 0.64 stance time Double Time in seconds / / 0.24 sec support time during the gait cycle that two feet are in contact with the ground Single support Time in seconds / / 0.38 sec time during the gait cycle that one foot is in not in contact with the ground Spatial descriptors of gait and their typical values for a right gait cycle. 20 Effect of speed on gait parameters Walking speed is related to both cadence and the stride length, so it can be increased by a more rapid cadence, longer stride length, or both. As speed increases the double support time (along with stance duration) decreases. stance phase is slightly longer while walking in bare feet compared to when wearing shoes. Shoes provide a slightly increased base of support, which helps balance. As balance is compromised, both stance and double support increase to provide an increased support time. This is an example of compensation strategy. 21  By increasing speed The following will increase The following will decrease Cadence Toe out angle Step length Stride width Stride length Stance time Single limb stance time Step time Swing time Stride time Double limb support time Running gait When double support reaches zero, running begins, and with further speed increase, the double support phase becomes negative (i.e.it becomes a flight phase). The fundamental unit for running is the stride cycle, which consists of all motions and events taking place between two consecutive foot- ground contacts of the same foot. Unlike walking, where the heel of the foot makes initial contact with the ground, during running, initial contact can occur at the rearfoot, midfoot, or forefoot and is frequently referred to as foot strike. The type of foot strike can influence the lower extremity joint kinematics during running. For example, a runner who uses a forefoot strike will have greater ankle plantar flexion and knee flexion at initial contact compared to rearfoot strike. Rearfoot strike is present in 88–95% of distance runners. Descriptor of Running gait Stride length and time change with running speed, such that stride length will increase and stride time will decrease with progressively faster running speed. Running pace, the inverse of speed, is typically measured in minutes per mile (min/mile) or minutes per kilometer (min/km). Among runners and coaches, running pace is more routinely used. 22  While walking speeds are generally less than 2.5 m/sec, running from 2.5 m/sec to greater than 10 m/sec. Running phases Only one limb at most is in contact with the ground at any instant during running. The stance phase of running is occupying about 40% of the stride cycle. As running speed increases, the stance phase portion progressively decreases There are two periods during the stride cycle when neither limb is in contact with the ground. These periods of float (or flight) occur after one limb has pushed off the ground and before the other limb has made initial contact. The increase in swing phase duration that accompanies an increase in running speed is primarily due to greater time spent in float. Running Stride cycle (stance and swing phases) Initial contact is the instant the foot contacts the ground, thereby defining 0% of the stride cycle. Mid stance occurs when the body’s center of mass (located anterior to the sacrum) is directly over the support limb, or when the knees are side by side. These both occur at about 20% of the stride cycle or 50% of stance phase. Heel off occurs at about 22–27% of the stride cycle toe off occurs at about 30–40% of the stride cycle. Mid swing occurs at the middle of the swing phase, roughly 70% of the stride cycle, when the knee of the swing limb passes next to the knee of the contralateral stance limb. 23 24 Periods of Running Stride Cycle Loading response occupies the first 15% of the stride cycle, between initial contact and the point of maximum knee flexion. During this period, the limb must gradually accept and absorb the weight of the body. Pre swing is from heel off to toe off when the muscles of the lower limb generate mechanical energy for propulsion (10%). Early swing refers to the first half of swing phase, from toe off to mid swing (30%). Late swing is the remainder of swing phase, from mid swing to the subsequent initial contact (30%). Float Float (or flight) occurs after one limb has pushed off the ground and before the other limb has made initial contact. Two float period, each is 10 %. They occur at the start and end of swing phase. one in the early swing and one in the late swing. 25 Sagittal plane kinematics across joints for each phase of the gait cycle Stance phase Sagittal plane kinematics at initial contact Joint/segment Degrees/position Ankle 0 degrees neutral Knee 0 ± 5 degrees Thigh (referenced to vertical) 25 degrees flexion Sagittal plane kinematics at loading response Joint/segment Degrees/position Ankle 5 degrees PF Knee 15 degrees flexion Thigh (referenced to vertical) 25 degrees flexion Sagittal plane kinematics at Mid stance Joint/segment Degrees/position Ankle 5 degrees DF Knee 0 degrees neutral Thigh (referenced to vertical) 0 degrees neutral 26  Sagittal plane kinematics at terminal stance Joint/segment Degrees/position Ankle 10 degrees DF Knee 0 degrees neutral Thigh (referenced to vertical) 15 degrees extension Sagittal plane kinematics at pre-swing Joint/segment Degrees/position Ankle 15 degrees PF Knee 40 degrees flexion Thigh (referenced to vertical) 0 degrees Neutral Swing phase Sagittal plane kinematics at initial swing Joint/segment Degrees/position Ankle 5 degrees PF Knee 60 degrees flexion Thigh (referenced to vertical) 15 degrees flexion 27  Sagittal plane kinematics at mid swing Joint/segment Degrees/position Ankle 0 degrees neutral Knee 25 degrees flexion Thigh (referenced to vertical) 25 degrees flexion Sagittal plane kinematics at terminal swing Joint/segment Degrees/position Ankle 0 degrees neutral Knee 0 degrees neutral Thigh (referenced to vertical) 25 degrees flexion 28 Angular displacment curve of ankle joint during gait cycle (Sagittal view) 29 Angular displacment curve of knee joint during gait cycle (Sagittal view) 30  Angular displacment curve of Thigh during gait cycle (Sagittal view) Primary determinants of gait Minimizing center of mass displacement Minimal displacement of the COM, both vertically and laterally, is optimal for smooth, efficient, forward progression. Minimizing its excursion conserves energy, increases efficiency, and reduces muscular effort. There are 6 essential motions as gait determinants, which minimized energy expenditure by reducing the excursion of the COM. Determinant is a various movement occurs in the body including pelvis, knee and ankle to maintain center of gravity of the body in a horizontal plane and ensure the smoothing pathway of gait. Pelvic rotation (transverse plane), pelvic list/obliquity (frontal plane), stance phase knee flexion, the interaction of the ankle and foot (plantar flexion, toe dorsiflexion), and hip adduction. During normal walking at a comfortable speed there is a double sinusoidal vertical trajectory of the COM displacing (2.5-5 cm). 31  It is highest during SLS (Mid Stance at 30% of the GC) and Mid Swing and lowest during DLS (Loading Response and Pre-Swing at 5% and 55% of the GC, respectively). Faster speeds increase the vertical COM excursion. Vertical center of mass displacement during one GC (5 cm) Lateral Center of Mass Displacement During normal walking at a comfortable speed there is a single sinusoidal lateral excursion of the COM. This displacement reflects the lateral shift of weight from one limb to another with maximum excursion in Mid Stance at 30% of the GC when weight is solely supported by the stance limb. The lateral shift is dependent on muscular stabilization of the hip and pelvis, so that pelvic drop and hip adduction are minimized. Lateral COM displacement during one GC (4 cm) 32  Kinematic strategies (Gait deteminants) during gait Benfits of Kinematic strategies during gait 1. Decrease the vertical and lateral displacement of center of gravity. 2. Increase the efficiency and smoothness of gait pathway 3. Degrease energy expenditure Optimization of energy expenditure ant its relation to walking speed Energy expenditure during gait is measured by the amount of energy used in calories per meter walked per kilogram of body weight. Typically, energy expenditure is measured indirectly by quantifying oxygen consumption. When walking, the body strives to minimize energy cost. Conservation of energy is achieved by optimizing the excursion of the CoG, controlling the body momentum, and taking advantage of intersegmental transfers of energy. The metabolic efficiency of walking is greatest at a walking speed of approximately 1.33 m/sec. Walking faster or slower than that optimal speed increases the energy cost of ambulation. 33  Energy-Saving Strategies of Walking (Gait determinants) 1) pelvic rotation The pelvis rotates alternatively to right and to left in relation to the line of progression in transverse plane about vertical axis. Forward rotation on swing and backward on stance phase The average magnitude of this rotation is approximately four degrees (4) on either side of the central axis. The total equal "8" degrees. Associated hip movement: Internal rotation (Stance) and external rotation (Swing). Function: Pelvic rotation during normal gait decreases the vertical displacement of by functional lengthening of the limb. 34 2) Pelvic tilting The pelvis tilts downward on swing leg (on the side which is opposite to that of weight bearing leg) along the frontal plane around sagittal axis. The maximum tilting is at mid-swing. The average magnitude: The average of the angular displacement is (5) five degrees. Associated hip movement: There are relative hip adduction in stance phase and hip abduction in the swing phase. Function: Pelvic tilting helps to decrease vertical displacement of center of gravity. 3) Knee flexion in the stance phase It has 3 functions by functional shortening of the limb: 1) Shock absorption. 2) Minimize displacement of COG. 3) Decrease energy expenditure. 35 4) & 5) Foot and knee interaction Early in the stance phase: The foot is dorsiflexed while the knee is almost fully extended. So, the extremity is at its maximum length and the center of gravity reaches its lowest point in a downward displacement. Late in the stance phase: The foot is plantar flexed while the knee is in the beginning of flexion. That will maintain the center of gravity in its beginning of progression with minimum displacement. 36 6) Hip adduction The amplitude of this lateral displacement, partially reflected by step width, is largely a function of frontal plane hip motion (i.e., hip abduction and adduction). The normally adopted 8- to 10-cm step width during ambulation reduces side to-side displacement of the body. Theoretically a step width greater than 8 to 10 cm provides greater stability at a cost of increased energy expenditure. It has been demonstrated that ambulation with either a lesser or a larger step width increases the energy cost of ambulation in young healthy individuals. Magnitude: 4 cm. Summary of the strategies Direction of Action Name of Strategy Action Vertical Horizontal plane Reduces the downward pelvic rotation displacement of the center of mass (CoM) Vertical Sagittal plane ankle Reduces the downward rotation displacement of the CoM Vertical Stance phase knee Reduces the upward flexion displacement of the CoM Vertical Frontal plane pelvic Reduces the upward rotation displacement of the CoM Side to side Frontal plane hip Reduces the side-to-side rotation (step width) excursion of the CoM 37 This figure illustrates the individual and additive effects of the kinematic strategies to reduce vertical center of mass (CoM) excursion. (A) illustrates the large vertical oscillation of the CoM while a person walks without the strategies. (B) illustrates that rotation of the pelvis in the horizontal plane functionally lengthens the lower extremities and reduces the magnitude of the hip flexion- extension angle required for a given step length, thereby reducing the downward displacement of the CoM. (C) illustrates that further reduction of the downward displacement of the CoM is achieved by rotation of the ankle in the sagittal plane. (D) illustrates that the small amount of knee flexion present during stance reduces the functional length of the lower extremity and therefore the upward displacement of the CoM. (E) shows that the contralateral pelvic drop during stance also reduces the net overall elevation of the CoM. 38  Instrumentations for gait analysis Three-Dimensional Gait Analysis Three-Dimensional Gait Analysis (3DGA) is a clinical tool which has become the gold standard in the objective assessment of walking. It aims to readily identify pathological components of a walking pattern through collection of movement, force, temporospatial and muscle activation data. A typical 3DGA includes computerised data collection encompassing three-dimensional kinematics (joint movement), kinetics (joint forces) and electromyography (EMG) (muscle activation), that is complemented by a comprehensive physical examination completed by an experienced physiotherapist. Following the 3DGA assessment, data are processed by the medical engineer and the relevant findings from the data are synthesised into a report by the specially trained physiotherapist; this summary is then further discussed by the multidisciplinary team (consisting of a medical engineer, physiotherapist, orthotist, an orthopaedic and/or neurological and/or rehabilitation medical consultant). The outcomes of the gait analysis data are discussed, and a recommended treatment plan formulated for the patient with all the information available. Treatment recommendations are based on the patient’s history, physical examination, the result of the gait analysis and consultant expertise. This is documented and disseminated in the form of written correspondence to the relevant treating team. 39  Kinematic Systems (Temporospatial parameters and angular displacement) Instrument Measurement Advantages Disadvantages In the field, a stopwatch and a measured Speed Portable, Easy Can’t provide distance complete TPs profile An optical or infrared detector (e.g. the Walking speed Portable, Easy An observer still Speedlight Timing System, SWIFT needed to count the Performance Equipment which turns a number of steps timer on and off when the subject breaks taken to calculate two light beams placed a known distance cadence and stride apart length A pedometer counts the number of The number of Portable, Easy Unfortunately, they steps, attached to the subject’s belt, steps are prone to over- and and counts each time they detect a underestimating. step. They are only useful for measuring the approximate number of steps taken over prolonged periods, i.e. activity monitoring. 3. FitSense FS-1 and Nike sdm Calculates the Long-term They are mainly uses Accelerometer and TSPs ambulatory aimed at runners to track their workout Gyrosensors. A wristwatch monitoring but can be useful calculates the TSPs after clinically, and the receiving radio signals from a data can be recorded small pod attached to the on the watch and downloaded later to a computer. 40 Instrument Measurement Advantages Disadvantages subject’s shoe. Stride Analyzer uses Footswitches Velocity, Portable, Easy ---------------------- on the toe and heel. They make an cadence, stride electrical contact when that part of length, the the foot is loaded. The temporal duration of parameters of gait (timing of initial single and contact, foot flat, heel rise and toe double support off, the duration of the stance phase for each limb, stance, swing and double support and the pattern times) of contact for each foot. Instrumented walkway, e.g. GaitMat II™ Complete TPs Portable, Easy ------------------- and GAITRite™ is used to measure the profile timing of foot contact and the position of the foot on the ground. The walkway contain a large number of switch contacts, which detect the position of the foot, as well as the timing of heel contact and toe off. This has the advantage that no trailing wires are required and the walkway can be used to measure both step lengths and the stride length. The GaitMat II uses an array of 38 rows × 256 switches to record each footfall GAITRite™ uses a pressure- sensing array arranged in 48 rows of 288 sensors to record the imprint of each footfall. The most common mat, 4 m long 41 Instrument Measurement Advantages Disadvantages Instrumentations for gait analysis (Angular displacement) Instrument Measurement Advantages Disadvantages 1-Electrogoniometer Joint ROM 1-The device may 1-They are subject to Electrogoniometers (sometimes be used in clinical types of error because called elgons) is an electronic version and occupational the electrogoniometer of an ordinary clinical goniometer. environments with is fixed by cuffs around high reproducibility the soft tissues, not to and accuracy. the bones, so that the output of the potentiometer does not exactly relate to the true bone-on-bone movement at the joint. 2-Some designs of electrogoniometer will only give a true measurement of joint motion if the potentiometer axis is aligned to the anatomical axis of the joint. This may not be achievable 42 Instrument Measurement Advantages Disadvantages 2- Biometrics Ltd uses flexible strain Joint ROM 1-It comes in a large 1-They require gauges makes an improved flexible variety of shapes cabling. electrogoniometer, which consists of and sizes. 2-They cannot measure two small end blocks connected to a 2-Inexpensive the absolute motion of 12–18 mm strain gauged metal strip 3-No need for a body segment. alignment with joint Examples of these are axis. motions of the pelvic and trunk, e.g. pelvic tilt and trunk flexion. Video Recording (2D) 1-Absolute 1-It reduces the 1-3D calculations are At least two cameras are used, motion of body number of walks a not possible. usually viewing the subject from one segment. subject need to do 2-Measurement errors side and the front/back. Additional 2- 2-Viewing the occur. cameras may be used to view both Tempororspatial patient from sides simultaneously, or from above. parameters of multiple angles All cameras are synchronized, and gait simultaneously can usually multiple camera views are also clarify the integrated into a single image using a patient’s movement frame splitter. Although video media patterns. are still in use, it is becoming more 3-It makes it easier common to record the images to teach visual gait digitally. analysis to someone Data is collected at a series of time else. intervals known as ‘frames’. For 4-Video recordings normal purposes, frame rates of 50 are used to augment Hz, 60 Hz or 200 Hz are used, but observational gait specialized systems running at higher analysis and provide speeds are also available. a degree of quality It is often helpful to mark the subject’s control for the skin, for example using an eyebrow motion capture data. pencil, to enhance the visibility of 5-Slow motion and anatomical landmarks on the even frame-by- recording. frame playback can be used as an Examples adjunct to Optical. Vicon Motion observational gait Systems analysis, enabling Ectromagnetic. FasTrak quick or subtle Ultrasonic. Zebris movements to be Inertial. xSense, inertial more readily measurement unit (IMU). detected. 43 Instrument Measurement Advantages Disadvantages Motion capture system (3D) (Vicon 1-Gait pattern 1-Provides 1-Expensive Motion Systems, Qualisys Pro Reflex 2-Angular kinematic data and 2-Requires specialized system). displacement body skeletons that software to help Television/computer systems use 3- can help analyse the process the reflective markers that are fixed to the Temporospatial movement. information obtained subject’s limbs, either close to the parameters of 2-Determines the through this joint centers or fixed to limb segments gait strengths and technology. in such a way as to identify their weaknesses of an 3-Scarcely available. positions and orientations. Close to athlete. the lens of each television camera is 3-No markers can an Infrared or visible light source, be misidentified. which causes the markers to show up as very bright spots that makes road signs show up brightly when illuminated by car headlights. GOLD STANDARD *Needs markers: -Passive markers for camera- based systems are generally made of a retroreflective material. This material is used to reflect light emitted from around the camera back to the camera lens. Some camera- based systems use a stroboscopic light, while others use light from synchronized infrared light- emitting diodes mounted around the camera lens. 44 Instrument Measurement Advantages Disadvantages -Cluster markers To circumvent the difficulties of inconstant movement and location of the skin markers, the use of a mid-segment cluster of markers has been introduced. The purpose is to define the plane of each segment with three markers and then track its movement through the basic reference planes. -Active markers It is a light emitting diodes (LEDs), and a special optoelectronic camera. These systems use invisible infra-red radiation. These light-emitting diodes (LED) are attached to a body segment in the same way as passive markers, but with the addition of a power source and a control unit for each LED. The camera measures the position of the marker by analyzing the light coming from it. Active markers can have their own specific frequency which allows them to be automatically detected. This leads to very stable real- time three-dimensional motion tracking as no markers can be misidentified as adjacent markers. Currently there are three commercial systems available (Selspot. Whatsmart, Optitrack). 45  Markers placement setup Examples of commercially available Gait analysis system GaitON® gait analysis system is used by clinicians to detect gait abnormalities & monitor gait changes in the patient. Its gait analysis protocol is based on RLA terminology & assesses the Pelvis, Hip, Knee & Foot motion during the Gait Cycle. Motion analysis system (Vicon system) 46  Kinetic gait analysis Ground reaction force (GRFV) During ambulation, forces are applied under the surface of the foot every time a person takes a step. The forces applied to the ground by the foot are called foot forces. Conversely, the forces applied to the foot by the ground are called ground (or floor) reaction forces. These forces are of equal magnitude but opposite direction. (Newton’s Third Law) Ground reaction force (GRF) has 3 components, each representing a different orthogonal direction (vertical, anterior/posterior [A/P] (fore/aft), and medio/lateral [M/L]). The GRFs are represented by a vector (ground reaction force vector [GRFV]), which is the result of adding the vertical force and shear forces. The sagittal plane GRFV is the addition of the vertical and A/P forces, while the frontal plane vector is composed of the vertical and M/L forces. During gait, the ground reaction forces applied under the foot generate an external torque on the joints of the lower extremities. Interpretation of joint demand using the position of the limbs relative to the GRFV that determine the external moments. The location of the GRFV, when superimposed on a walking figure, can help visualize the external moments created at the lower limb joints. The origin of the GRFV is a single point referred to as the center of pressure (COP) and represents the location of net moments occurring within the base of support (BOS). 47  Sagittal plane GRFV in red, vertical component in blue, and A/P (fore-aft) component in green. Frontal GRFV in red, vertical component in blue, and M/L component in green. Determination of Joint Moments (Joint torque) Determination of Joint external Moments External moments are calculated, and internal moments defined and designated by the predominant muscle groups that are presumed active. 48 Link Segment Model Using Inverse Dynamics An inverse dynamics analysis is typically based on measurement of the kinematics of the body segments, often complemented with measurement of selected external forces (e.g. the ground reaction force). Using these data, the net joint torques, and net joint reaction forces are calculated using Newton’s equations of motion applied to a model containing a chain of rigid segments. During the loading response on the right limb, the line of action of the ground reaction force is located behind the ankle and knee but anterior to the hip. Consequently, the ground reaction forces at heel contact produce ankle plantar flexion, knee flexion, and hip flexion. To prevent collapse of the lower extremity, these external torques are resisted by internal torques created by the activation of the ankle dorsiflexors, the knee extensors, and the hip extensors. Only with intramuscular electromyography (EMG) recordings can one be certain that specific muscles are active, and hence contributing to the force component. Internal torque The activation of muscles creates most of the internal torques that control joint motion, especially in midrange positions. This internal torque is associated with concentric muscle activation when the joint moves in the direction of the muscle’s action. Internal torque is associated with eccentric muscle activation when the joint moves in the direction opposite the muscle’s action. Internal torques can also be created by passive forces generated by the deformation and recoil of connective tissues, such as the capsule, tendons, and ligaments. It is not always possible to state with certainty the relative contribution of active and passive forces to the 49  prevailing internal torque across a joint. In the middle of the range of motion active muscles produces most of the internal torques. Near the end of the range of motion, contributions of both active and passive structures may need to be considered. The term net internal joint torque in attempts to account for coactivation of agonist-antagonist muscle groups. For example, the flexion torque produced by the hip flexor muscles during the swing phase may be associated with slight (eccentric) activation of muscles that extend the hip. In theory, this extensor torque subtracts from the hip flexion torque, thereby yielding a net flexion torque. Sagittal plane kinetics during stance phase 50 Joint/ GRFV EXTERNAL MUSCLE Segment VISUALIZATION MOMENTS ACTIVITY Ankle Anterior DF Con of PF Knee Posterior Flexion Rectus femoris Hip Posterior Decreasing Hip flexors extension 51  Sagittal plane moments by joint PHASES EXTERNAL SAGITAL ANKLE MOMENTS Initial Contact Minimal PF Moment &Loading Response Eccentric dorsiflexor activity peaks to control PF and initiate forward movement of the tibia, contributing to knee flexion (Tibialis anterior) Mid Stance DF Moment Eccentric plantarflexors activity (Gastrocnemius and Soleus) Terminal Stance Peak DF Moment Highest activity of plantarflexors Eccentric then concentric at 40% of gait cycle Pre-Swing Decreasing DF Moment Concentric contraction of the plantar flexors continues to diminish DF moment as ankle plantar flexes then plantarflexors activity quickly ceases Onset of dorsiflexor activity prepares for swing DF clearance Initial Swing, Mid Minimal PF Moment Swing, Terminal Dorsiflexor concentric activity brings the ankle to neutral Swing by Mid Swing for foot clearance and isometric activity during terminal swing. PHASES EXTERNAL SAGITAL KNEE MOMENTS Initial Contact Extension Moment Vasti remain active concentrically in preparation for loading Loading Flexion Moment Response Vasti eccentric activity Mid Stance Decreasing flexion moment and then becomes an extension moment. The vasti extend knee, but cease activity when GREV moves anterior to the knee Terminal Stance Decreasing extension moment and then an increasing flexion moment that initiates Pre-Swing knee flexion Pre-Swing and Flexion Moment Initial Swing Rectus femoris eccentric activity to decelerate knee flexion Terminal Swing Extension Moment Vasti activity in preparation for Initial Contact and Loading Response, and to counteract the hamstring eccentric activity decelerating the limb 52 PHASES EXTERNAL SAGITAL HIP MOMENTS Initial Flexion Moment Contact & Eccentric hamstring activity at the start of initial contact followed by Loading concentric hip extensor activity (Gluteus maximus and hamstring) Response Early Flexion Moment then Extension Moment Mid Concentric activity decreases and the anterior hip structures Stance (ligaments) passively resist the moment as the hip is extending by momentum Terminal Extension Moment Stance Passively resisted by the anterior hip structures Decreasing Extension Moment Pre-Swing, Concentric flexors activity (Adductor longus initiates hip flexion in Initial Pre-Swing), Iliopsoas activates at initial swing, the rectus femoris Swing, activates later in Mid Swing to flex the hip while limiting knee Mid flexion. The hamstring in late Mid Swing act eccentrically to Swing: decelerate the limb in preparation for Initial Contact. Flexion Moment Terminal Hamstring eccentric activity to decelerate limb to prepare for Swing Initial Contact. Center of Pressure (COP) Center of Pressure (COP) represents the net moments acting within the BOS and is visualized as the intersection of the GRFV with the floor. During quiet stance, the A/P and lateral coordinates of the COP and COM coincide because there is little movement. Once dynamic motion occurs, they follow opposite trajectories. The path of the center of pressure (CoP) under the foot throughout stance follows a relatively reproducible pattern. (The term pressure is used to describe the ground reaction force related to its specific area of application.) 53  At heel contact, the CoP is located just lateral to the midpoint of the heel. It then moves progressively to the lateral midfoot region at mid stance Then moves to under the first or second metatarsal head) during heel off to toe off. A centre of pressure (CoP) pathway is shown by the position of the black dot at initial contact (A), at foot flat (B), just before heel-off (C), and just before toe-off (D). Normal plantar distribution during standing and walking When making measurements beneath the feet, it is important to distinguish between force and pressure (force per unit area). Some of the measurement systems measure the force (or ‘load’) over a known area, from which the mean pressure over that area can be calculated. However, the mean pressure may be much lower than the peak pressure within the area if high pressure gradients are present, which are often caused by subcutaneous bony prominences, such as the metatarsal heads. In bare foot assessment, the largest pressure in the entire foot was in the heel regions. The mean peak heel pressure was about 2.6 times greater than the forefoot values. 54 Weight distribution In a typical foot the peak pressure (of about 140 kPa) is located under the heel, and pressures under the ball of the foot are some 2.5 times lower. This results in about 60% of the load being carried by the rearfoot, 8% by the midfoot, and 28% by the ball of the foot. The use of the toes is minimal with an average of less than 4% of the load. The largest pressure under the forefoot is generally located under the second metatarsal head. Typical pressures beneath the foot are 200–500 kPa in walking and up to 1500 kPa in some sporting activities. In diabetic neuropathy, pressures as high as 1000–3000 kPa have been recorded. To put these figures into perspective, the normal systolic blood pressure, measured at the feet in the standing position, is below 33 kPa (250 mmHg); applied pressures which are higher than this will prevent blood from reaching the tissues. Data interpretation When making pressure measurements beneath the feet is that a subject will normally avoid walking on a painful area. Thus, an area of the foot which had previously experienced a high pressure and has become painful may show a low pressure when it is tested. However, this will not happen if the sole of the foot is anesthetic, as commonly occurs. In this condition, very high pressures, leading to ulceration, may be recorded. 55  Plantar pressure in other foot types Planus feet displayed higher pressure, force and contact area values in the medial arch, central forefoot and hallux, while these variables were lower in the lateral and medial forefoot. In contrast, cavus feet displayed higher pressure in the heel and lateral forefoot and lower pressure, force and contact area in the midfoot and hallux. Instrumentation for gait analysis (Ground reaction force, muscle myoelectrical activity and plantar pressure) Instrument Measurement Advantages Disadvantages 1-Force plates (3D) Applied force Precise and Needs a lot of Force plates measure the force applied to the ground to the ground accurate cabling. by the feet as the patient walks over them. They by the feet. measure force in three-dimensional. This information is integrated with the body kinematics defined by the motion capture system to assess the mechanics of movement. At least two plates are required if both limb functions are to be analyzed from a single walk, a desirable but not always achievable goal. Strain gage force plates (e.g., AMTI: temperature sensitive) Piezoelectric force plates (e.g., Kistler force plates: they are subject to drift and moisture affects cables and connectors) 56 Instrument Measurement Advantages Disadvantages The vertical forces are directed perpendicular to the supporting surface. These vertical ground reaction forces peak twice in a given gait cycle. Forces are slightly greater than body weight at the time of early stance and again after heel off At mid stance, the vertical ground reaction forces are less than body weight because of a relative “unweighting” caused by the upward momentum of the body gained during the early part of stance. The higher ground reaction force at push off reflects the combined push provided by the plantar flexors and the need to reverse the downward movement of the body that occurs in late stance. The force is typically normalized by body weight (Newton [N]/Body Weight [BW]). 2-Electromyography (EMG) EMG The Muscle activity Helps doctors 1-Cannot be during gait. diagnose used to electromyography (EMG) system is used to record muscle and distinguish the activity of muscles during gait, a process referred nerve between disorders. Isometric, to as dynamic EMG. concentric or EMG is generally recorded using either passive or eccentric contractions. active surface electrodes. 2-pick up Active electrodes have a built-in amplifier signals from and are less susceptible to artifacts due to other active wire motion. muscles in the The methods of recording the EMG surface general area of and needle electrodes. application. This feature makes surface 57 Instrument Measurement Advantages Disadvantages electrodes the ideal choice for analysis of global activity in superficial muscles or muscle groups. 3-sensitive to movement of the skin under Surface electrodes: Used to convenient, the electrodes measure the easy to apply and have poor activity of to the skin specificity. surface and do not They are muscles or cause pain, influenced by muscle groups. irritation, or significant discomfort to muscle ‘cross- the subject talk,’ in which the electrode signals of one muscle interfere with the signals from another. 4-Surface electrodes cannot readily be used to detect the activity of deep muscles, e.g., the tibialis posterior. In addition, surface EMG is subject to cross-talk, particularly when a rather small muscle is adjacent to larger muscles with overlapping firing patterns, e.g., the rectus femoris. They are sensitive to movements of the skin and 58 Instrument Measurement Advantages Disadvantages have poor specificity. Used to Highly 1-Invasive Fine wire electrodes: measure the selective of electrodes can activity of deep the activity of be painful and muscles specific lead to muscles and infections. the influence 2-Needs a lot of of nearby cabling. muscles is 3-Pain on reduced. insertion. 4-Difficulty of accurate placement. 5-A license is needed to utilize them. Electromyography If the EMG of deep muscles is required, fine wire electrodes are used. EMG may be captured simultaneously with motion capture or separately. EMG determines if the activity of a muscle is phasic with clear on and off periods, or is nearly constant, either on or off, indicating absence of useful control or if the muscle activity occurs at the normal time in the gait cycle. Once the EMG data are acquired, they must be processed further to provide information about the timing of muscle activity and the relative intensity of the muscle activity. 59  The EMG data are recorded throughout the gait cycle. The gait cycle is indicated either with synchronization of the kinematic data, foot- switch information, or force-plate data to indicate each foot strike and toe-off. Analysis of the EMG is done by a phase–time plot of the activity of the muscle against events of the gait cycle. The raw EMG signal can be analyzed or processed further. The most common methods of EMG signal processing are full-wave rectification, linear envelope and integration of the rectified EMG. Full wave rectification reverses the sign of all negative voltages and yields the absolute value of the raw EMG. The linear envelope is created by low-pass filtering the full wave-rectified signal. Normalization is based on the maximum manual muscle test or maximum EMG signal obtained during gait. The muscle is activated when at least 5 % of the maximum electrical activity obtained during a manual muscle test is present for 5 per cent of the gait cycle. 60  EMG deviations (Timing) EMG deviations (Intensity) Pressure beneath the foot The measurement of the pressure beneath the foot is a specialized form of gait analysis, which may be of value in conditions in which the pressure may be excessive, such as diabetic neuropathy and rheumatoid arthritis. Foot pressure measurement systems may be either floor mounted or in the form of an insole within the shoe. Instrument Qualities Glass plate examination Semi-quantitative Subject walks or stands on a glass plate viewed from below by a mirror or television camera. Easy to see which areas of the sole of the foot are in contact with the plate. Blanching of the skin gives an idea of the applied pressure. Inspection of both the inside and the outside of a subject’s shoe will also provide useful information about the way the foot is used in walking; it is a good idea to ask patients to 61  wear their oldest shoes when they come for an examination, not their newest. Direct pressure mapping Semi-quantitative system Low-tech methos for measuring foot (e.g., The Harris or Harris- pressure. Beath mat) Made of thin rubber, Highest ridge under the lowest pressure. Lowest ridge under the highest pressure. The pedograph An elastic mat on top of an edge-lit glass plate. The area gets darker as the pressure applied on it increases. Different colors respond to different levels of pressure. The underside of the glass plate is usually viewed by a television camera, the monochrome image being processed to give a ‘false-color’ display, in which different colors correspond to different levels of pressure. Pressure sensor The subject walks across an array of force system (Tekscan) sensors to measures the vertical force beneath a particular area of the foot. Includes: Resistive, Capacitive and strain gauges, conductive rubber, Piezoelectric materials and a photoelastic optical system. Several different methods have been used to display the output of such systems, including the attractive presentation. In-shoe devices Flexible inserts between the foot and the (Pedar) shoe. Subdivided into several regions and each region is instrumented to measure the local force. Has lower resolutions than fixed plates. Orthotics may be evaluated under conditions of actual use. Measurements for several steps may be obtained Disadvantages: Lack of space for the transducers. The measurements are affected by how the foot, shoe, and insert fit, and the load sensors tend to be less precise and less uniform than those used in the floor-mounted platforms. The need of many wires from the inside of the shoe to the measuring equipment. 62  Metabolic Function Instrument Qualities Calorimetry Measures the amount of energy consumed while walking by: -measuring the O2 consumed -Measuring the CO2 produced These determine if the patient may benefit from conditioning or if an intervention has improved gait efficiency. Compact, portable and comfortable. The results are affected by fatigue, diets and general conditions. Treadmill Used to observe gait for longer times at higher speeds. Can be used alongside the motion capture systems to measure the patient’s kinematics. Measures the vertical component of the GRF. Force plates and pressure sensors