Biomechanics 1st Lecture PDF

# Biomechanics 1^st Lecture ## Biomechanics - The scientific study of human motion. - Kinesis means to move, Ology means science. - Kinesiology comes from 3 bodies of knowledge: - Anatomy - Physiology - Biomechanics ## Biomechanics: - The study of mechanical principles affect...

# Biomechanics 1^st Lecture ## Biomechanics - The scientific study of human motion. - Kinesis means to move, Ology means science. - Kinesiology comes from 3 bodies of knowledge: - Anatomy - Physiology - Biomechanics ## Biomechanics: - The study of mechanical principles affecting human body at rest or in motion. The study of biomechanics covers 2 basic areas: ## Kinematics - A branch of mechanics that describes the motion of the body without regard to the forces or torques causing the motion e.g. velocities and acceleration - The basic 2 types of Kinematic are quantitative and qualitative analysis. - Qualitative analysis deals with naming and evaluating movement component. - Quantitative is concerned with counting and measuring movement component. ## Kinetics - A branch of mechanics that describes the effects of forces on the body - The basic 2 types of kinetics are statics and dynamics: - Statics is studying of body remaining at rest or in a state of equilibrium brought about by balanced forces. - Dynamics the study of moving body under the effect of unbalanced forces. This information is also represented in the following diagram: **Diagram:** - A tree diagram showing Biomechanics branching into Kinematics and Kinetics - Kinematics: - Descriptive analysis - Qualitative analysis: Naming and evaluating movement components - Quantitative analysis: counting and measuring movement components - Kinetics: - Causal analysis - Static: study of body in state of rest - Dynamic: study of body in state of motion ## Forces - A force can be simply defined as: __Physical quantity that tends to change the state of the object to__: - Maintain the object in its equilibrium. - Or to disturb its equilibrium. - Or to change the shape of the object. - It is a push or pull that can produce stop or modify movement. - To cause these changes the force does work. - Anything that could do a work is called a force. - The quantity of force is the product of mass (m) multiplied by acceleration (a) of the mass F=ma - The unit of force is Newton (N) - A force is a vector quantity having both magnitude and direction. - A force can be represented graphically by an arrow (vector). - This vector has 4 characteristics - 1- Magnitude: Indicated by the length of the arrow. - 2- Line of force application: - Indicated by the angle of the arrow with a reference line - The angle of muscle insertion: Is the line of muscle force application and it is the angle between: - the tendon of a muscle and - The long axis of bone to which it inserts. - 3-Direction: It is indicated by the arrow's head. - 4-Point of application: It is where the base of the vector arrow contacts the part of the body. The point of application of muscle force is its insertion point. **Diagram:** - Diagram that shows a line with an angled arrow pointing up with the following text: - FORCE = MASS X ACCELERATION - θ - COMPONENTS OF A FORCE VECTOR - • POINT OF APPLICATION (INSERTION) - • MAGNITUDE - • DIRECTION - Diagram with two circles divided by a line. The left circle is labeled "__Internal Forces__" and the right circle is labeled "__External forces__" and arrows are drawn to represent the forces inside both circles. ### Internal Forces: - Internal forces are produced from structures located within the body. - These forces may be active or passive. - 1- Active forces are generated by muscle. - 2-Passive forces are generated by tension in stretched connective tissues as ligaments and joint capsules. - Joint reaction force is an example of internal forces. ### External forces: - External forces are produced by forces acting from outside the body. - These forces usually originate from either: - Gravity - Or an external load (as free weight) - Or physical contact (as force applied by the therapist against the limb of a patient) #### a-The force of gravity - Equals the weight of the body - (W=m (kg) ×g (m/s²) where g g is the gravitational constant (9.8m/s²). - Its direction is downwards - Line of application is perpendicular to the ground. - Its point of application is at the center of gravity #### b-The ground reaction force: - Equal in magnitude and opposite in direction to the body weight. - Its point of application is at the contact between the foot and the ground. **Diagram:** - Diagram with two stick figure representations. On the left, figure A is standing with gravity labeled and the ground reaction force is labeled. On the right, figure B is walking with gravity and ground reaction force labeled. #### C-Friction: - Friction is another type of external forces. - When 2 surfaces are pressed together a force is required to make one surface slide over the other. - The resistance to this force developed at the surface of contact is called frictional force. **Diagram:** - Diagram showing friction acting on a box that is moving to the right. - Diagram of a box on a surface with forces of gravity, friction, and normal labeled. #### d- Resistance: - A force which tends to reduce movement or to stop a moving object. - It is directly related to the surface area. - To improve body movement either in air or in water the resistance must be reduced for example long jump. #### e- Pressure: - Is defined as total force applied per unit area (P=F/A) and its unit of measurement is N/m² or Pascal. - By enlarging the area of contact, the same force can be spread over a much larger area so reducing the pressure. - In standing the area of contact is less than lying position. - For bed ridden patients we have to increase the area of contact. **Diagram:** - Diagram of a force in contact with an area. An arrow points from the force towards the area. - Diagram with the text: FORCE/AREA = PRESSURE ## Muscle Force - The size and shape of the muscle affect the magnitude of the force exerted by this muscle. - The physiological cross sectional area and the pennation angle are major determinants of range and force produced by the muscle. ### -Effect of cross sectional area of the muscle on muscle force: - The thicker the muscle, the greater the force potential. - The muscle force is proportional to the sum of the cross sectional area of all fibers. **Diagram:** - Diagram showing two muscles: - muscle A: with a smaller cross sectional area and muscle length labeled - muscle B: with a larger cross sectional area and muscle length labeled. ### -Effect of shape of the muscle on muscle force: - There are 2 common shapes of muscle fusiform and pennate. - Fusiform muscle: has fibers running parallel to each other and to the central tendon as biceps brachii. - In pennate muscles: The fibers approach the central tendon obliquely. **Diagram:** - Diagram showing a fusiform muscle labeled "Fusiform BICEPS" with additional diagrams of: - unipennate - bipennate - multipennate - Pennate muscles produce greater maximal force than fusiform muscles of similar size. Example of tripennate muscle that generates very large forces is the gastrocnemius muscle. - One advantage of pennate muscles is that more muscle fibers can be packed in parallel, thus allowing the muscle to produce more force. - The part of muscle force that actually affects movement is the force in the muscle’s tendon. - Since pennate muscle fibers aren’t parallel to the tendon, the muscle force that acts on muscle attachments is a component of the actual force in the fibers ## Muscle strength: - is the maximum ability of the muscle to lift weight for one time. - It is the maximum force (tension) which the muscle can produce per unit cm² (PCS). - It was found that each cm² of the muscle could produce muscular tension of 3-4 kg and up to 9kg. - If a muscle has PCS of 10 cm², its muscle strength reaches 90 kg. cm². - The magnitude of muscle strength (force) changes according to: - The shape of muscle fibers - Cross sectional area - Sex: Strength is higher in males than females. - Age: Aging process decrease muscle strength. ## Types of muscular activation: ### 1) Concentric (shortening) activation: - In this case the muscle shortens, as the internal forces generated by the muscle are greater than the external forces applied. - The muscle produces positive work on the external load (Work= force × distance). - The movement occurs against gravity and the joint moves toward the inner range. - Concentric contraction produces the lower magnitude of muscular force. That is because there is direct relationship between the muscle length and the tension produced by the muscle. As the muscle length decreases, the tension decreases. ### 2) Eccentric (lengthening) activation: - In this case, the muscle lengthens because the external forces are greater than the internal force. The contractile units of the same muscle control this lengthening. - Eccentric contraction produces negative work on the muscle. - Eccentric contraction produces the highest magnitude of muscular force because the muscle length increases. ### 3) Isometric activation: - In isometric activation, the overall muscle length remains constant. - The internal forces generated by the muscle equal the effects of the external forces. - When a muscle act isometrically, no mechanical work is done as a load is not moved and no joint movement is produced. - Although there is no joint movement and no mechanical work, fatigue is produced due to generation of metabolic work (accumulation of lactic acid and other metabolites). - Isometric contraction produces intermediate magnitude of the muscular force (more than concentric and less than eccentric). |**Type of muscle contraction**| **concentric** | **Eccentric** | **Isometric** | |---|---|---|---| | **Muscle length** | Decrease | Increase | No change | | **Gravity** | Against gravity | With gravity controlled and slowly | Against gravity | | **Joint movement** | Movement towards inner range | Movement towards outer range | No movement of the joint | | **Internal and external force** | Internal force > External force | External force > Internal force | External force-Internal force | | **Mechanical work** | Positive work | Negative work | No mechanical work but metabolic work | | **Tension** | Lowest | Highest | Inbetween | | **Difficulty** | Difficult | Easy | moderate | | **Line of application of muscle force:** | | | | - The line of force application is represented by the angle of pull or angle of insertion of the muscle. - This angle changes according to the change of the angular position of the joint. - For example: When the elbow joint is moved through its range, the angle of pull of the flexor muscle (biceps brachii) changes. - __Resolution of force:__ Is the process of resolving a force into 2 components perpendicular to each other (Fy and Fx) so as to complete the diagram (rectangle or parallelogram). - Fy=F sin 30 - Fx=F cos 30 - To show the effect of the muscle at different joint angles, the muscular force can be resolved into 2 components perpendicular to each other. - 1- Rotatory component: This tends to rotate the part around the joint. It is F sin - 2- Non rotatory component: This is directed towards the joint and so it is called stabilizing or compressive component. It is F cos Ө **Diagram:** - Diagram showing a muscle with a force arrow and two vectors drawn, one labeled "rotary component" and the other labeled "stabilization component". - A second diagram is provided showing a muscle with a force and two vectors drawn again. One vector is labeled "rotary component" and the other is labeled "distraction component". - Diagram with the text: "Stabilization Vs. Ditraction Component" - __Composition of forces:__ It is the process of finding one single force that shows the combined effect of 2 or more forces. - The single force is called Resultant ## Torques - Much of the movement in the human body is rotational. Limb segments rotate at joints and muscles apply torques and the skeleton acts as a system of levers. - This means that we need to know about rotational movement. As you will see rotational movement is very similar to linear movements with rotational analogues for the quantities we measured for linear motion. - A complete description of movement of a body needs to include both linear and rotational components and these can be largely treated separately. - Torques is the rotational equivalent of forces. The unit of torque is the Newton. Meter and it is defined as force acting at a distance from an axis of rotation. - The distance is the perpendicular distance from the line of action of the force to the axis of rotation (this is also the shortest distance between the line of action of the force and the axis of rotation). - T= Fr - Tis the torque (Nm) - Fis the magnitude of the Force (N) - r is the perpendicular distance from the axis of rotation (m) - In the body muscles apply linear forces at their attachment points. The shortest distance of the line of action of the force from the joint axis is also known as the moment arm of the muscle. - The torque applied by the muscle is the product of its tension and the moment arm. It is often the case that the moment arm of a muscle changes as the degree of flexion or extension at a joint change. Thus the maximum torque that can be generated also changes. **Diagram:** - Diagram showing a fulcrum with a torque arm and force causing torque labeled. - Diagram showing a stick figure with a force and torque labeled. The text "M=F.d" is also drawn.