Biomechanics Week 8.docx

Biomechanics Week 8: Gait Kinetics and Kinematics Gait: pattern of movement that allows animal during locomotion to move across a solid substrate. You can analysis the gait of humans and animals. Type of locomotion: crawling, walking, running, hopping and skipping.   Gait cycle In lamens terms, 2 st...

Biomechanics Week 8: Gait Kinetics and Kinematics Gait: pattern of movement that allows animal during locomotion to move across a solid substrate. You can analysis the gait of humans and animals. Type of locomotion: crawling, walking, running, hopping and skipping.   Gait cycle In lamens terms, 2 steps. There is initial contact and toe off. For running, the key event may be toe off. The time interval between two successive occurrences of the same event of locomotion. Ie: walking a few steps. Key phases of the gait cycle: stance and ends with toe off, then the swing phase which is the toe off to the initial contact of the opposite foot 60% stance and 40% swing phase We then have sub phases and events GO BACK OVER THE INDIVIDUAL SUB PHASES. The stance phase has 4 sub phases The swing phase has 3 sub phases. Heel strike = initial contact. Certain conditions, eg: cerebral palsy may start on toes. Stance and swing % begins to change as our speed/velocity increases and there is more time spent in a swing phase. 1 stride = 2 steps. Walk 1.5m/s = 60% stance, 40% swing Race walk 3m/s = 50/50 Run 5.m/s = 30% stance, 70% swing Spring 9m/s = 20% stance, 80% swing Walking has a period of double support = 2 foot contact with the ground. Running doesn't have this.   Gait Terms Step length: whichever leg is leading in the swing phase. Stride length: Step time: Stride time: distance in between 2 feet Cadence: frequency Stride width (walking base): Foot angle (toe out): Stride time (s) = 1/stride frequency (Hz) Ipsilateral: term used for the limb being studied Contralateral: term used to describe the mechanics of the opposite limb   Gait Velocity Stride velocity (m/s) = stride length (m)/ stride time (s) = stride length (m) x stride frequency (Hz)     KEY KINEMATICS Initial Contact (the image had the right foot leading, for context) Trunk: behind leading foot, crosses midline toward the stance leg, right pelvis forward Hip: flexed Knee: extended, starting to flex Ankle: neutral Foot: supinated Contact to the ground through the heel results in a most vertical force vector acting through the heel and ankle. Not quite plantar flexed or supinated at this point. The knee will be extended and the hip will be flexed.   Loading Response Start of the double support period Body has travelled over the supporting leg and the force vector is now going through the heel, passing through the knee but is still in front of the pelvis. The foot is starting to pronate and tibial internal rotation is happening. There will be some lateral trunk shift towards the stance leg to help balance and stabilise the body Trunk: lowest vertical position, moving laterally towards the stance leg Hips: beginning to extend Knee: flexing Ankle: plantar flexing Foot: pronation (eversion) and tibial internal rotation.   Foot Flat (Contralateral Toe Off) End of first double support period. The contralateral limb is at toe off and the stance limb now has the pelvis more over it, the foot is flat on the ground and the ankle is dorsi flexing cause the tibia is moving over the foot. The force vector is passing behind the knee and just in front of the pelvis. Trunk: begins to gain height, right pelvis coming back to neutral Hip: extending (25 degrees flexion) Knee: flexing Ankle: dorsiflexing as tibia moves over foot Foot: pronation (eversion) and tibial internal rotation peak   Mid Stance The weight has shifted forwards to the middle of the foot. The force vector is now passing through the middle of the foot and through the knee and stance leg. We only have a vertical force at this point in time. The tibia has moved into external rotation and the tibia is moving forward over the foot and cause the knee has reached peak flexion, it will start to extend. This is when centre of gravity is highest. Trunk: trunk reaches highest point, peak lateral motion of trunk, pelvis passes through neutral Hip: extending Knee: reaches peak knee flexion and begins extension Ankle: dorsiflexing as tibia moves over foot Foot: supination (inversion) and external rotation of tibia.   Terminal Stance Now have second double support occurring Period from ipsilateral heel off to contralateral foot contact - also called "push off" When the heel leaves the ground this is really when propulsion and horizontal forces occur. You're about to shift your body weight to the other limb Trunk: moving to the opposite side Hip: reaches its most extended position Knee: moving back into flexion Ankle: plantarflexing Foot: reaches maximal supination   Initial Swing Period from toe off through to feet adjacent The force vector is passing through the very last point of the toe on the original staring leg and in the direction of forwards and upwards, will pass through the proximal end point of the tibia, behind the knee and behind the hip. On the left side (all the below happens). Trunk: trunk moving through neutral toward the new (left) supporting foot, trunk gains height Hip: flexing Knee: flexing (mainly due to flexion of hip - pendulum) Ankle: moves from plantarflexion to neutral or dorsiflexed position Foot: slightly supinated   Terminal Swing (late swing) Period from feet adjacent through to initial foot contact provided toe clearance has occurred, ankle is pretty neutral. Trunk: moves from maximal displacement on left side back toward midline and trunk loses height Hip: flexion (rate of flexion decreasing) Knee: rapid knee extension (mostly passive) Ankle: once toe clearance achieved ankle position not as important Foot: remains in supination.   Sagittal plane kinematics (photo in phone, I have this textbook) A hip angle is the thigh segment angle - the trunk segment angle Trunk angle segment from the greater trochanter of the femur bone through to the iliac crest. Thigh segment: greater trochanter to the femoral condyle Positive hip angle = flexion Negative hip angle = extension For the ankle, you need to measure shank - foot + 90 degrees.   Sagittal plane motion (need to rewatch this part) (photo in phone) What's normal? Peak hip extension occurs in terminal stance of the gait cycle Data collected for men showing data around normal amounts of flexion and extension.   Frontal Plane Kinematics We don't use supination and pronation, inversion and eversion are used. Rear foot = shank - calcaneus Positive rear foot = inversion Negative rear foot = eversion   Sub-Talar Joint Motion Normal range of motion, 5 degrees of pronation and 4 degrees of supination.   Determinates of gait There are 6 There aim to minimise the excursion of COM Pelvic rotation: hip and pelvis movement. There is rise and fall happening in the vertical direction, this happens as more weight shifts over the stance limb Pelvic obliquity: pelvis will tip up and down during the gait cycle. Tips in the frontal plane, it will move downward during swing and up during stance. Tries to help reduce vertical movement in COM. We want a little bit of movement to help dissipate forces and reduce back load. Stance phase knee flexion: adjusting the length of leg during the stance phase to maintain hip height. Works to keep the hip at a stable height Ankle mechanism: lengthening of the leg at initial contact and toe off. Tries to lengthen the leg to help keep the hip height stable Foot mechanism: external rotation of the leg and supination of the foot lengthening the leg at toe off. Lateral displacement/genu valgum: we don't walk as robots. We have slight valgus at the knee to help reduce side to side movement as we walk.   Typical Values (normal walking for adults 20-59 years) 2.2 m/s, about 8kms per hour Cadence: 112-120 steps per minute Stride length: 1/22 - 1.53m Velocity: 1.20 - 1.45 m/s Double ST: 20-25%   Walking vs running No double limb support phase Running has 2 float periods Stance swing ratio changes Increased hip and knee flexion and increased plantar flexion in running to increase propulsion   Running Stance 30% Swing 70% Swing sub phases: early float, mid swing, late float Recovery phase: from toe off through to knee flexion and knee alignment Drive phase: drives forward, through to initial contact.   Normal Rearfoot Motion (go back over this too) Occurs slightly on the lateral side of the heel Foot in neutral alignment and then begins to move in pronation which occurs for about 70% of the ground contact phase, with max pronation occurring around 40% of the phase. Then supination starts, the heel rotates inwards Gait: stance phase and swing phase. New terms and old terms. Sub phases Initial contact force creates the positive vertical force and a negative horizontal force. When added together, is a force that acts backwards but upwards. At mid stance, there's a vertical force acting upwards, horizontal force is = 0. At toe off, there's positive vertical force acting upwards through the body and positive horizontal force as it's acting in the way you're travelling.   Ground reaction forces Vertical 2 hill shape for constant velocity walking and the 2 hills are equal in magnitude. Double support phase on a diagram indicates it's walking not running. There will be a cross over. F1: upward deceleration of COG (peak arrest). Aka weight acceptance. Rate of change in the force/weight in time F2: COG moving over the stance limb (mid stance). Push off rate. F3: upward acceleration (propulsion) of the COG (peak thrust)   Horizontal (anterior posterior) Dip and hill shape F4: peak braking (arrest) F5: Mid support (Fy = 0 BW due to change of direction) F6: Peak propulsion (thrust)   In early stance phase In normal gait, there's a force vector acting slightly behind the knee Quad contraction is important in early stance phase During clinical gait analysis, there's 2 abnormal things that may be detected: Anterior trunk bending: when the force vector is acting in front of the knee. Occurs when trunk flexion is occurring throughout the whole gait cycle and can be a result of poor quad strength. Posterior trunk bending: the force vector passes behind the knee and hip. This occurs when there is trunk extension at the line of heel contact and is due to poor hip extensor strength.   Ground reaction force patterns can change with increasing velocity. The vertical force curve changes the most, the horizontal force curve doesn't change that much but the magnitude and time of each may change. Running patterns: the impact peak is smaller than the active peak Running downhill: impact peak become larger and active peak gets smaller. For the horizontal forces: breaking peak becomes more dominant than propulsive. Uphill running: more pronounced active peak and greater propulsive forces.   Medial Lateral Direction (Fx) Small dip and wide hill shape F7: max supination (lateral direction) F8: max pronation (medial direction) Medial directed force is positive and lateral is negative for the right limb and opposite for left limb Less sensitive to changes in force with walking speed.   GRF Variability Makes it hard to be precise with measurements Nothing to do with equipment, it's about movement of the person This is why the Fx direction isn't always analysed.   *moment here is looking at the torques occurring within the body   Initial Contact Hip: extension moment (generating power) Knee: flexion moment (short period of power generation) Ankle: neutral GFR is acting upwards through the knee and ankle joint. There's a neutral ankle position, no moment occurring here. At the knee, there's a flexion moment and at the hip there's an extension moment.   Loading Response The GRF vector is acting through the middle of knee and slightly in front of the femur. At the ankle, it's moving from negative to positive, the knee is still negative and the hip is still positive. The ankle is the only thing that's changed. Hip: extension moment (generating power) Knee: flexion moment (short period of power generation) Ankle: posterior force vector = external plantarflexion moment   Mid stance The force vector is behind the knee but in line with the hip. There is some initial power absorption replacing generation in the knee. Hip: extension moment decreasing Knee: posterior force vector = external knee flexion moment, initial power absorption replaced by generation Ankle: increasing plantarflexion moment, absorbing power.   Terminal Stance The resultant force vector is behind the knee and hip. Generation stage at the ankle. The hip is now in a negative moment. Hip: flexion moment (passive tension), mostly power absorption but moving towards generation. Knee: flexion moment, moving to extension moment to limit rate of knee flexion (absorption) Ankle: high plantarflexion moment (generation)   Initial Swing Hip: flexion moment and power generation Knee: flexion due to pendulum = knee extension moment and power absorption Ankle: decreasing moment and power   Terminal Swing No GFR occurring here. Hip: increasing extension moment Knee: increasing flexion moment and power absorption Ankle: neutral   Joint Power Patterns Corresponds to the gait cycle Important in clinical gait analysis   Braking Phase H1: hip extensor power generation (concentric). From glute max and hamstrings K1: knee joint power absorption (eccentric). From quads K2: knee extensor power generation (concentric). From quads A1: ankle power absorption (eccentric). From triceps surae (gastroc and soleus)   Propulsion Phase H2: hip flexor power absorption (eccentric) A2: ankle plantarflexion power generation (concentric) K3: knee extensor power absorption (eccentric). From rectus femoris.   Swing Phase H3: hip flexor power generation (concentric) Knee extensor power absorption (eccentric) Knee extensor power generation (concentric). From quads.   Frontal and Transverse Plane Kinetics The goal of locomotion is to support the body against gravity whilst moving forward in the plane of progression. Need full 3D motion analysis   Plantar pressure Indirectly reflect accelerations of all body parts as we walk Will be unique to everyone. Often look at the peak pressure in zones of the foot. Modified Arch Index (MAI) and COP Excursion Index (CPI)   Muscle Activity (EMG) Gives an overall perspective of when muscles are turned on and off   Activity of all muscles go towards propulsion and breaking during the gait cycle The Achilles can experience up to 6-8 x BW in forces through it.   Energy Source The sources of power generation for forward propulsion provides insight on the strategy of movement Hips are powerful extensors during the second half, the knee flexors are for the first. Movement strategy changes with increasing speed.   Spine pathways in Gait In running or walking, the hip extensors fire as the toe pushes the ground The muscle is directly transmitted to the spine and trunk via two distinct but complementary pathways Firing the hip extensors extends and raises the trunk in the sagittal plane.   Causes of Inefficient movement Co contractions: muscles fighting against each other Isometric contractions against gravity: segments are held in isometric contraction Generation of energy at one joint and absorption at another: one joint is making positive energy and another negative Jerky movements: very start and stop.