Week 3 Movement Science PDF Study Guide

Study Guide: Osteokinematics and Degrees of Freedom 1. Osteokinematics Overview Osteokinematics refers to the movement of bones around joints within the three cardinal planes. These movements are associated with specific axes of rotation and can be categorized into two primary types: translation (l...

Study Guide: Osteokinematics and Degrees of Freedom 1. Osteokinematics Overview Osteokinematics refers to the movement of bones around joints within the three cardinal planes. These movements are associated with specific axes of rotation and can be categorized into two primary types: translation (linear) and rotation (angular). Cardinal Planes of Movement 1. Sagittal Plane ○ Divides the body into left and right halves. ○ Movements: Flexion and Extension ○ Example: Bending forward (flexion) or standing up straight (extension). 2. Frontal Plane ○ Divides the body into anterior and posterior parts. ○ Movements: Abduction and Adduction ○ Example: Raising arms to the side (abduction) or bringing them down (adduction). 3. Horizontal Plane ○ Divides the body into superior and inferior parts. ○ Movements: Rotation (medial and lateral) ○ Example: Turning your head left or right. Axes of Rotation 1. Anterior-Posterior Axis ○ Runs from front to back. ○ Associated with movements in the sagittal plane (e.g., flexion and extension). 2. Medial-Lateral Axis ○ Runs from side to side. ○ Associated with movements in the frontal plane (e.g., abduction and adduction). 3. Vertical Axis ○ Runs from top to bottom. ○ Associated with movements in the horizontal plane (e.g., rotation). 2. Types of Motion Translation (Linear Motion) All points on an object travel the same distance in the same direction at the same time. Example: Sliding your hand across a table. Rotation (Angular Motion)  Motion occurs around an axis, following an arc or circle. Example: Rotating your arm around the shoulder joint. Curvilinear Motion A combination of linear and rotary motion. Example: Sliding down a curved slide. The motion includes both translatory and rotary components. 3. Common Clinical Terms and Exceptions Abduction and Adduction Standard Abduction/Adduction: Movement away from or toward the body's midline. Fingers and Toes: ○ Fingers: Use the middle finger as the reference for abduction/adduction. ○ Toes: Use the big toe as the reference. Horizontal Abduction and Adduction Occurs in the Transverse Plane: Movement of a body part forward or backward relative to the midline when the limb is flexed at 90 degrees. Example: Bringing a flexed arm toward or away from the body’s midline. Wrist Movements Ulnar Deviation: Wrist movement toward the ulna (adduction). Radial Deviation: Wrist movement toward the radius (abduction). Ankle Movements Inversion: Movement of the ankle towards the midline (similar to adduction). Eversion: Movement of the ankle away from the midline (similar to abduction). Pronation and Supination Pronation: Radius rotates over the ulna; involves some degree of eversion, adduction, and plantar flexion. Supination: Radius rotates back to its original position; involves inversion, adduction, and dorsiflexion. Opposition and Circumduction Opposition: Thumb movement towards the pinky; involves flexion and adduction. Circumduction: A circular movement combining flexion, extension, abduction, and adduction, typically seen in the thumb. 4. Degrees of Freedom Degrees of freedom describe how many planes a joint can move within. Shoulder (Glenohumeral Joint): 3 degrees of freedom ○ Movements: Flexion/Extension, Abduction/Adduction, Rotation. Elbow: ○ Humeroulnar Joint: 1 degree of freedom (Flexion/Extension). ○ Humeroradial Joint: 1 degree of freedom (Pronation/Supination). Wrist: ○ 2 degrees of freedom ○ Movements: Flexion/Extension, Radial/Ulnar Deviation. 5. Practical Applications Identifying Planes and Axes Be able to identify which plane of motion is being discussed and the corresponding axis of rotation. Example: Flexion of the elbow occurs in the sagittal plane around a medial-lateral axis. Measurement Tools Goniometer: Used to measure angles of rotary motion in degrees. 6. Review Questions 1. What plane of movement is shoulder flexion occurring in? ○ Answer: Sagittal Plane. 2. Which axis does ankle inversion occur around? ○ Answer: Anterior-Posterior Axis. 3. How many degrees of freedom does the wrist have and what movements are involved? ○ Answer: 2 degrees of freedom (Flexion/Extension and Radial/Ulnar Deviation). 4. Describe curvilinear motion with a human anatomical example. ○ Answer: Opening the mouth involves initial rotation and later translation. Study Guide: Clinical Applications of Osteokinematics Objectives 1. Understand Goniometry: Learn how to use goniometers to measure osteokinematic motion. 2. Define End-Feel Types: Identify and describe different types of end-feel and their clinical significance. 3. Compare Open vs. Closed Kinematic Chains: Understand the concepts and clinical examples of open and closed kinematic chains. 1. Goniometry Definition: Goniometry is the measurement of joint angles to quantify the range of motion (ROM) of joints. Purpose: To measure both active (muscle-driven) and passive (externally driven) motion. Goniometer: ○ Components: Stationary Arm: Remains fixed (e.g., along the humerus for elbow flexion). Moving Arm: Follows the moving segment (e.g., along the radius for elbow flexion). Axis: Positioned over the joint being measured. ○ Types of Motion: Active Motion: Movement instigated by the individual's muscle contraction. Passive Motion: Movement achieved through external forces, such as therapist assistance or gravity. Example: Measuring elbow flexion using a goniometer where the stationary arm is aligned with the humerus, and the moving arm tracks the radius. Clinical Application: Essential for evaluating joint function, documenting progress, and setting rehabilitation goals. 2. End-Feel Definition: The sensation perceived by a therapist when the joint is moved to its end range. It helps determine the type of resistance met.  Types of End-Feel: ○ Hard End-Feel (Bony): Description: Movement is stopped by bone-on-bone contact. Example: Elbow extension where the olecranon process fits into the olecranon fossa of the humerus. ○ Firm End-Feel (Capsular): Description: Movement is stopped by tension in the joint capsule or ligaments. Example: Wrist flexion where the end feels "springy" due to the tension in wrist ligaments. ○ Soft End-Feel: Description: Movement is stopped by the approximation of soft tissues, typically muscle. Example: Elbow flexion where the biceps and forearm come into contact. Pathologic End-Feel: ○ Hard End-Feel: If detected in an area where soft tissue approximation should occur (e.g., knee flexion). ○ Empty End-Feel: Pain limits motion without a specific end-feel (e.g., due to fracture or inflammation). Clinical Application: Identifies normal vs. abnormal joint function and helps diagnose joint pathologies. 3. Open vs. Closed Kinematic Chains Definition: Describes how segments of the body move relative to each other and their fixation to external objects. Open Kinematic Chain: ○ Description: The distal segment (e.g., foot) is free to move, while the proximal segment is fixed. ○ Example: Knee flexion in a seated position where the foot is free to move. ○ Clinical Application: Exercises like leg extensions where the foot is not fixed, focusing on isolated joint movements. Closed Kinematic Chain: ○ Description: The distal segment is fixed to the earth or another immovable object, causing the proximal segment to move. ○ Example: Squats where the foot is fixed on the ground, and the hip moves. ○ Clinical Application: Exercises like squats or push-ups where the body is supported and movement involves multiple joints. Challenges:  Chain Analogy Limitations: The body is not a simple linear chain; it has branching segments and varying external resistance. Task Demands: Some activities, like walking or running, involve both open and closed chain phases depending on the phase of movement. Practical Exercise Examples: Open Chain: Chest fly, heel rise with weights. Closed Chain: Push-ups, squats, and variations like plank push-ups. Summary Understanding goniometry, end-feel, and kinematic chains provides a foundational grasp of joint motion and its clinical implications. By practicing these concepts, you can better assess, diagnose, and treat musculoskeletal conditions. Next Steps: Practice: Use goniometers in practical settings to measure joint ranges. Assess End-Feel: During physical exams, identify different end-feels and correlate them with potential joint issues. Analyze Kinematic Chains: Apply the concepts of open and closed kinematic chains to various exercises and functional movements to understand their impact on joint mechanics. Additional Resources: Videos: Review videos on push-ups, elbow step-ups, and variations to see examples of open and closed chain activities. Textbook Figures: Refer to figures that illustrate different types of motion and end-feel. Feel free to revisit specific sections or ask questions during synchronous sessions to clarify any doubts! Study Guide: Arthrokinematics 1. Objectives Define and differentiate arthrokinematics from osteokinematics. Define joint play (accessory motion) and describe its clinical application. Interpret and explain the concave-convex rule. Understand and demonstrate closed-packed vs. open-packed joint positions. 2. Key Concepts Arthrokinematics vs. Osteokinematics Arthrokinematics ○ Definition: Motion occurring between joint surfaces. ○ Focuses on how the surfaces of joints move relative to each other. Osteokinematics ○ Definition: Motion of bones around a joint axis. ○ Focuses on overall bone movement and is typically what is measured in exercises. Types of Arthrokinematic Motion 1. Rolling (Rocking) ○ Definition: Rotary motion where multiple points on one surface contact multiple points on another surface. ○ Example: Shoulder abduction involves the humeral head rolling on the glenoid fossa. ○ Analogy: Rolling a bowling ball or soccer ball. 2. Sliding (Gliding) ○ Definition: Linear motion where a single point on one surface contacts multiple points on another surface. ○ Example: Shoulder abduction also involves a sliding motion of the humeral head in the glenoid fossa. ○ Analogy: An ice skate gliding on ice. 3. Spinning ○ Definition: Rotational motion where a single point on one surface contacts a single point on another surface. ○ Example: Radius spinning on the capitulum of the humerus during pronation and supination. ○ Analogy: Spinning a top or basketball on a finger. Note: Most joint movements involve a combination of rolling, sliding, and spinning. Joint Play (Accessory Motion) Definition: Small, involuntary movements within a joint necessary for full range of motion. Joint Compression ○ Description: Moving joint surfaces together. ○ Purpose: To assess joint stability (e.g., McMurray test for meniscus tears). Joint Distraction ○ Description: Pulling joint surfaces apart. ○ Purpose: To increase joint mobility (e.g., Lachman test for ACL integrity). Convex-Concave Rule Convex-on-Concave ○ Rule: Roll and slide occur in opposite directions. ○ Example: During knee flexion, the convex femoral condyles roll posteriorly and slide anteriorly on the concave tibial plateau. Concave-on-Convex ○ Rule: Roll and slide occur in the same direction. ○ Example: During tibial movement (open chain), the concave tibia rolls and slides in the same direction on the convex femur. Closed-Pack vs. Open-Pack Positions Closed-Pack Position ○ Description: Joint surfaces are tightly fit against each other, with maximum surface contact and minimal accessory motion. ○ Characteristics: Ligaments and joint capsule are under tension, making it difficult to distract the joint. ○ Example: Full knee extension. Open-Pack Position ○ Description: Joint surfaces do not fit perfectly, allowing for greater accessory motion and joint play. ○ Characteristics: Ligaments and capsule structures are more relaxed. ○ Example: Slight knee flexion (20-30 degrees), which allows for easier joint distraction and assessment. 3. Practical Applications Tests and Measurements McMurray Test ○ Application: Assess for meniscus tears using joint compression. ○ Procedure: Externally rotate the tibia and apply a valgus force for the medial meniscus or internally rotate for the lateral meniscus.  Lachman Test ○ Application: Assess the integrity of the ACL using joint distraction. ○ Procedure: Block the femur with one hand while pulling the tibia superiorly with the other hand to test for ACL integrity. Instantaneous Axis of Rotation Definition: The center of rotation of a joint is not fixed but moves throughout the joint’s range of motion. Evolute: The path traced by the instantaneous axis of rotation as the joint moves. Clinical Implication: Understanding that our measurements with goniometers are approximations and that the actual axis of rotation may vary. 4. Study Tips Visualize: Use diagrams and videos to understand rolling, sliding, and spinning at different joints. Practice: Perform physical assessments and tests like the McMurray and Lachman tests to reinforce understanding. Review: Revisit the convex-concave rule with different joint examples to ensure clarity. 5. Reflection and Practice Identify Positions: Experiment with different joint positions (e.g., hip, knee) to feel and identify open-packed and closed-packed positions. Analyze Movements: Observe and analyze the roll, slide, and spin motions in various joints and movements. Study Guide: Introduction to Kinetics Slide 1: Introduction to Kinetics Objective: 1. Define kinetics. 2. Differentiate between kinetics and kinematics. 3. Identify the four forces acting on the body. 4. Differentiate between mass and weight. Slide 2: Definition of Kinetics Kinetics: ○ Definition: The study of forces acting on material bodies, including the human body. ○ Material Bodies: Can refer to the whole body, body segments (like fingers or ankles), or specific joints (like the shoulder or knee). ○ Forces: Actions that produce, arrest, or stop motion. Slide 3: Kinetics vs. Kinematics Kinematics: ○ Definition: The study of motion without considering the forces that cause it. ○ Focus: Describes the movement of bodies and segments in terms of displacement, velocity, and acceleration. Kinetics: ○ Definition: Focuses on the forces that cause or affect motion. ○ Focus: Examines the effects of forces on motion, including magnitude and direction. Exercise: Compare and contrast kinematics and kinetics to understand their distinct roles in movement science. Slide 4: Types of Forces 1. Internal Forces: ○ Example: Muscle contractions within the body. ○ Characteristics: Can generate motion or stabilize joints. 2. External Forces: ○ Examples: Gravity, external objects (dumbbells), external resistance (manual resistance by physical therapists). Slide 5: Magnitude and Direction of Forces Magnitude: ○ Definition: The quantity of force (e.g., measured in pounds, Newtons, or other units). Direction: ○ Components: Positive and negative directions. ○ Axes: X-axis: Left and right (medial-lateral). Y-axis: Up and down (superior-inferior). Z-axis: Anterior and posterior. Slide 6: Axes of Rotation and Osteokinematic Motion Medial-Lateral Axis (ML Axis): ○ Description: Runs from left to right. ○ Motion: Flexion and extension. Anterior-Posterior Axis (AP Axis): ○ Description: Runs from front to back. ○ Motion: Abduction and adduction. Vertical Axis: ○ Description: Runs up and down. ○ Motion: Rotation. Slide 7: Practical Application of Forces Example: Tug of War: ○ Analysis: Identify internal and external forces. ○ Considerations: Magnitude and direction of forces; effects of equal vs. unequal forces. Slide 8: Types of Forces and Their Applications 1. Gravity: ○ Definition: The force exerted by the Earth that affects all objects. ○ Example: Increases weight when holding a dumbbell. 2. Muscle Forces: ○ Active Forces: Muscle contractions. ○ Passive Forces: Stretching of muscles due to their viscoelastic properties. 3. External Resistance: ○ Examples: Pulleys, dumbbells, doors, manual resistance in muscle testing. 4. Friction: ○ Definition: The force resisting motion between two surfaces in contact. Slide 9: Mass vs. Weight Mass: ○ Definition: The amount of matter in an object, constant regardless of location. ○ Example: Mass is the same on the Moon and Earth. Weight: ○ Definition: The force of gravity acting on an object, varies with gravitational pull. ○ Example: Weight is less on the Moon compared to Earth, and less at higher altitudes compared to sea level. Slide 10: Measurement Units  Mass: ○ SI Unit: Kilograms (kg). ○ US/UK Term: Slug (less commonly used). Weight: ○ Units: Pounds (lb), Newtons (N). Slide 11: Important Terms 1. Moment: ○ Definition: The product of force and distance. ○ Formula: Moment = Force × Distance. 2. Moment Arm: ○ Definition: The perpendicular distance between the axis of rotation and the line of force. 3. Torque: ○ Definition: The product of force and moment arm in rotary motion. ○ Example: Torque on a wrench involves rotating around a circular axis. Slide 12: Example: Reducing Torque Scenario: Adjusting moment arm length to reduce stress on a joint. ○ Top Image: Longer moment arm (4.5 feet). ○ Bottom Image: Shorter moment arm (4 feet). ○ Effect: Reducing the moment arm decreases torque, reducing joint stress. Slide 13: Summary and Review Recap: ○ Kinetics vs. Kinematics: Forces vs. motion. ○ Types of Forces: Internal, external, gravity, muscle, friction. ○ Mass vs. Weight: Amount of matter vs. gravitational force. ○ Moment, Moment Arm, Torque: Definitions and applications. Review Points: ○ Understand force magnitudes and directions. ○ Be able to analyze forces in practical scenarios. ○ Differentiate between mass and weight in various contexts. This guide follows the structure of your lecture and should help in consolidating the key concepts covered. Feel free to add more details or examples based on your needs! 4o mini Study Guide: Newton's Laws and Biomechanics I. Introduction to Newton's Laws Objectives: 1. Define Newton's laws of motion. 2. Understand the concept of the center of mass (center of gravity). 3. Learn about mass moment of inertia (MMOI) and its alteration. 4. Apply Newton's second law to rotary motion. 5. Define Newton's third law and explore examples. II. Newton's First Law: The Law of Inertia Definition: Newton's First Law states that an object remains at rest or continues moving at a constant velocity unless acted upon by an external force. This principle applies to both linear and rotational motion. Key Terms: 1. Inertia: ○ Definition: The property of matter that resists changes to its state of motion. ○ Relation to Mass: Inertia is directly proportional to mass; greater mass means greater inertia. 2. Center of Mass (Center of Gravity): ○ Definition: The point where mass is evenly distributed and where gravitational forces act. ○ Location in Human Body: Just anterior to the sacrum (often referred to as the belly button in casual terms). Center of Mass in Body Segments: Individual Segments: The center of mass does not change within a body segment (e.g., femur, lower leg, foot). Entire Extremity: The center of mass of the whole limb shifts with movement. For example, when lifting a leg, the center of mass of the entire leg moves posteriorly and superiorly. Mass Moment of Inertia (MMOI):  Definition: MMOI indicates an object's resistance to changes in its angular velocity. Dependence: It depends on both the mass of the object and the distribution of mass around the axis of rotation. Implications: 1. Reducing MMOI: Results in increased angular velocity. This is beneficial in sports and physical activities where quick movements are necessary. 2. Example - Running Shoes vs. Boots: ○ Running Shoes: Typically lighter, resulting in lower MMOI and faster running speed. ○ Army Boots: Heavier, leading to higher MMOI and reduced speed. Applications: 1. Baseball Batting: ○ Choking Up on the Bat: Reduces the MMOI by shortening the moment arm, increasing the bat's angular velocity. 2. Diving: ○ Tucking vs. Spreading Limbs: Tucking limbs reduces MMOI, allowing for faster spins compared to spreading limbs, which increases MMOI and slows down rotation. III. Newton's Second Law: The Law of Acceleration Definition: Newton's Second Law states that the acceleration of an object is directly proportional to the force applied and inversely proportional to the mass of the object. The formula is: F=maF = maF=ma where FFF is force, mmm is mass, and aaa is acceleration. Application to Rotary Motion: Torque: Analogous to force in linear motion, torque is the rotational equivalent. It is calculated as: Torque=Force×Moment Arm\text{Torque} = \text{Force} \times \text{Moment Arm}Torque=Force×Moment Arm where the moment arm is the perpendicular distance from the axis of rotation to the line of action of the force. Angular Acceleration: Torque causes angular acceleration, which is proportional to the applied torque and inversely proportional to the mass moment of inertia. Formula for Torque: Torque=MMOI×Angular Acceleration\text{Torque} = \text{MMOI} \times \text{Angular Acceleration}Torque=MMOI×Angular Acceleration Key Points:  Angular Acceleration: Is inversely proportional to the mass moment of inertia. Smaller MMOI leads to faster angular acceleration. IV. Newton's Third Law: The Law of Action-Reaction Definition: Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that any force exerted on an object results in a force of equal magnitude but in the opposite direction. Examples: 1. Walking with Crutches: ○ When a person exerts a downward force on the ground with crutches, the ground exerts an equal and opposite force upward, which supports the person. 2. Injury Example: ○ If a person jumps and lands heavily on their foot, the ground exerts an equal and opposite force upward, which can cause injury if the force exceeds the structural capacity of the foot (e.g., a broken toe). Applications: Understanding Injuries: Helps in understanding how forces during physical activities can result in injuries due to the equal and opposite reaction forces. Summary: 1. Newton's First Law involves inertia and the center of mass, emphasizing resistance to changes in motion. 2. Newton's Second Law relates force, mass, and acceleration, applicable to both linear and rotary motion. 3. Newton's Third Law highlights action-reaction pairs, explaining how forces result in equal and opposite reactions. Understanding these principles is crucial for analyzing and optimizing human movement in various fields, including biomechanics, physical therapy, and sports science. Study Guide: Biomechanics and Vectors in Physical Therapy I. Introduction Objective: Understand the role of vectors in biomechanics and how they apply to clinical settings. II. Vectors: Definition and Components 1. Definition: Vector: A quantity that has both magnitude and direction, represented graphically by an arrow. 2. Components of a Vector: Magnitude: The size of the force, indicated by the length of the arrow. Direction: Indicated by the arrowhead, showing the direction of the force. Spatial Orientation: The position of the arrow's shaft, which can affect whether the vector is positive or negative. Point of Application: The location where the base of the vector arrow contacts the body. This is important because gravity acts on the center of mass of the body segment. Illustrative Example: Traction and Compression Forces: ○ Traction Force: Positive superior force acting on the cervical spine. ○ Compression Force: Negative force due to the weight of the head acting downwards. III. Combining Vectors 1. Resultant Force (RF): Definition: The combined effect of multiple forces acting in the same direction. Clinical Example: Combining forces from a boot weight, leg weight, and a disk weight in knee extension exercises. Summing these forces gives the resultant force. 2. Joint Reaction Force:  Definition: The force exerted by a joint that is equal and opposite to the resultant force due to Newton's Third Law. Illustrative Example: Cervical Spine Traction: ○ Positive Force (Traction): +25 pounds. ○ Negative Force (Head Weight): -10 pounds. ○ Resultant Force: 25 pounds - 10 pounds = 15 pounds. IV. Vector Resolution 1. Definition: Vector Resolution: The process of breaking a vector into its component forces, typically X (horizontal) and Y (vertical) components. 2. Importance: Y Component: Causes torque or rotation. X Component: Causes compression or distraction but does not produce torque. Illustrative Examples: Brachioradialis Muscle: Forces are resolved into X and Y components to analyze torque and joint stability. Biceps Muscle: Depending on joint angle, the X component might cause compression or distraction. V. Torque and Moment Arms 1. Definition: Torque: The rotational effect of a force about a joint or axis. Calculated as: Torque=Force×Moment Arm\text{Torque} = \text{Force} \times \text{Moment Arm}Torque=Force×Moment Arm Moment Arm: The perpendicular distance between the axis of rotation and the line of action of the force. 2. Application: Example: Straight leg raise vs. knee flexion. ○ Extended Leg: Larger moment arm, higher torque.  ○ Flexed Knee: Reduced moment arm, lower torque required. VI. Clinical Applications 1. Designing Exercises: Objective: To maximize or minimize muscle strength or torque based on vector analysis. Exercise Comparison: Evaluate which exercise position requires more force production based on internal and external moment arms. 2. Manual Muscle Testing: Objective: Determine how the location of resistance affects muscle force production. Resistance Placement: Mid-shaft vs. lower ankle; how each affects the force the muscle has to produce. VII. Practice Questions 1. Design an Exercise: ○ Compare two exercise positions (A and B) for biceps strength. Consider changes in weight, internal moment arm, external moment arm, and joint angle. 2. Manual Muscle Testing: ○ Analyze the effect of resistance placement on quadriceps strength. Consider resistance amount and location (mid-shaft vs. distal). VIII. Conclusion Summary: Understanding vectors, combining forces, and calculating torque are crucial for effective biomechanical analysis in physical therapy. Next Steps: Apply these concepts in practical scenarios and clinical exercises to optimize patient outcomes. End of Study Guide Study Guide: Biomechanics - Levers and Mechanical Advantage Lecture Overview This study guide covers the second half of biomechanics, focusing on the types of levers and the concept of mechanical advantage. The key points include understanding the three classes of levers, how they are applied in the human body, and the role of mechanical advantage in clinical settings. 1. Types of Levers 1.1. General Concept of a Lever Definition: A lever is a simple machine consisting of a rigid bar (the lever arm) pivoted about a fixed point (the axis of rotation). It is used to transmit force and convert linear force into rotary torque. Components: ○ Axis of Rotation: The fixed point around which the lever rotates. ○ Internal Force: The force applied by muscles. ○ External Force: The resistance or load that is to be moved. 1.2. First Class Lever Description: The axis of rotation is positioned between the internal and external forces. Example: A seesaw. Biomechanics: In a first class lever, the moment arms (distance between forces and the axis of rotation) can be equal or different. For equilibrium, the force magnitude must balance the resistance. Human Body Example: The head and neck. The neck extensor muscles apply an internal force, while gravity acts as the external force. The axis of rotation is at the atlanto-occipital joint. 1.3. Second Class Lever Description: The axis of rotation is located at one end of the lever, and the internal force has greater leverage than the external force. Example: A wheelbarrow or standing on tip-toes. Biomechanics: The internal moment arm (force arm) is longer than the external moment arm (resistance arm), providing a mechanical advantage.  Human Body Example: The action of the gastrocnemius and soleus muscles when standing on tip-toes. The force arm from these muscles is larger compared to the resistance arm affected by body weight. 1.4. Third Class Lever Description: The axis of rotation is located at one end of the lever, but the external force has greater leverage than the internal force. Example: Holding chopsticks or a book. Biomechanics: The external moment arm is larger than the internal moment arm, leading to a mechanical disadvantage where more muscle force is required. Human Body Example: The biceps brachii at the elbow. The internal moment arm (from the muscle) is shorter compared to the external moment arm (from the weight held in the hand). 2. Mechanical Advantage 2.1. Definition Mechanical Advantage (MA): The ratio of the length of the internal moment arm (force arm) to the length of the external moment arm (resistance arm). MA = Internal Moment Arm / External Moment Arm. 2.2. First Class Levers Mechanical Advantage: Can be less than, equal to, or greater than 1 depending on the relative lengths of the moment arms. ○ Example: If the internal moment arm is 4 cm and the external moment arm is 3.2 cm, MA = 4 / 3.2 = 1.25. This means less force is needed from the muscle compared to the load. 2.3. Second Class Levers Mechanical Advantage: Always greater than 1. The internal moment arm is longer than the external moment arm. ○ Example: In standing on tip-toes, the internal moment arm (12 cm) compared to the external moment arm (3 cm) gives MA = 12 / 3 = 4. Thus, less muscle force is needed to lift the body weight. 2.4. Third Class Levers Mechanical Advantage: Always less than 1. The external moment arm is longer than the internal moment arm.  ○ Example: Holding a book with the biceps, where the internal moment arm (5 cm) compared to the external moment arm (35 cm) results in MA = 5 / 35 = 0.143. More muscle force is required to lift the weight. 3. Clinical Implications of Mechanical Advantage 3.1. Adjusting Mechanical Advantage Therapist's Role: Physical therapists can alter the external moment arm by adjusting the position where resistance is applied during muscle testing. Surgeon's Role: Surgeons can alter the internal moment arm by repositioning tendons to increase or decrease the torque that a muscle can produce. 3.2. Benefits and Downsides Increasing Internal Moment Arm: Can increase torque output for weak muscles (e.g., in post-polio syndrome) but may reduce the angular displacement and velocity of movement. Example: Moving a tendon further from the joint center increases the force a muscle can generate but might reduce the joint's range of motion and speed of movement. 4. Examples for Practice 4.1. Exercise Design Question: Design an exercise to maximize biceps strength. Compare the force production required between different positions of the arm. Factors to Consider: Weight, internal and external moment arms, and joint angles. 4.2. Manual Muscle Test Question: When performing a manual muscle test on the quadriceps, compare the effect of placing resistance at mid-shaft vs. around the ankle. Factors to Consider: Impact on muscle force production and resistance placement in relation to the joint. Conclusion This lecture on levers and mechanical advantage covers the types of levers, how they function biomechanically, and their clinical significance. Understanding these concepts helps in designing effective exercises and interventions for patients, optimizing their functional outcomes. Feel free to reach out with questions or for further clarification during our synchronous session. 4o mini