Biomechanics Lab Exam Review

Electromyography (& the gait cycle):

1. What is Electromyography?

   1. Electromyography (EMG) is a technique used to measure and record the electrical activity produced by muscles.

   2. EMG provides information about the timing and intensity of muscle activation, which can be used to understand how muscles are used during movement.

2. What does EMG measure?

   1. EMG measures the electrical activity of muscle fibers, which is caused by the movement of ions across the cell membrane.

   2. The amplitude and duration of the EMG signal can be used to determine the level of muscle activation.

3. How is the skin prepared for surface EMG?

   1. The skin must be cleaned and dried to remove any oil or sweat, which can interfere with the recording of the EMG signal.

   2. Electrodes are then placed on the skin, usually in a specific pattern, to pick up the electrical activity of the underlying muscles.

4. How can you design a research project to evaluate which muscles are active during a given movement?

   1. First, identify the movement you want to study.

   2. Then, choose the muscles you think are involved in that movement.

   3. Use EMG to record the electrical activity of those muscles during the movement.

   4. Analyze the EMG data to determine which muscles are most active during different phases of the movement.

5. What are the steps necessary to get from raw data to processed data?

   1. Raw EMG data is typically noisy and difficult to interpret.

   2. To process the data, it must be filtered to remove noise and artifacts.

   3. The EMG signal can then be rectified and smoothed to make it easier to analyze.

   4. Finally, the processed data can be analyzed to determine muscle activation patterns and other parameters of interest.

6. What are the clinical applications of EMG?

   1. EMG is commonly used in clinical settings to diagnose muscle and nerve disorders, such as neuropathy and myopathy.

   2. EMG can also be used to evaluate muscle function in patients with neuromuscular diseases, such as cerebral palsy and muscular dystrophy.

7. What are the gait cycle's major events, periods, and phases and their relative timings and intervals?

   1. The gait cycle consists of two main periods: stance phase and swing phase.

   2. Stance phase is further divided into four phases: heel strike, foot flat, midstance, and toe off.

   3. Swing phase is divided into two phases: initial swing and terminal swing.

   4. The relative timings and intervals of these phases vary depending on the individual and the movement being studied.

8. How can you develop hypotheses for the roles of various muscles during the gait cycle?

   1. First, identify the muscles involved in the movement.

   2. Then, consider the timing and intensity of muscle activation during different phases of the gait cycle.

   3. Use this information to develop hypotheses about the roles of different muscles in the movement, such as providing stability, propulsion, or shock absorption.

Forces:

1. What are Newton’s three laws and how can they be applied to different activities?

   1. Newton’s first law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by a net external force.

   2. Newton’s second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

   3. Newton’s third law states that for every action, there is an equal and opposite reaction.

   4. These laws can be applied to a wide variety of activities, from sports to transportation to space exploration.

2. What is force and what are its characteristics?

   1. Force is a push or pull on an object.

   2. The characteristics of a force include its direction, magnitude, and point of application.

3. How do you draw a complete free body diagram?

   1. A free body diagram is a diagram that shows all the forces acting on an object.

   2. To draw a complete free body diagram, you must identify all the forces acting on the object and their directions, magnitudes, and points of application.

4. How can you calculate forces?

   1. Forces can be calculated using Newton’s second law: F = ma, where F is the net force, m is the mass of the object, and a is its acceleration.

5. What is static equilibrium and how can you apply it to solve force problems?

   1. Static equilibrium occurs when an object is at rest and there is no net force acting on it.

   2. To solve force problems using static equilibrium, you must identify all the forces acting on the object and ensure that the net force is zero.

6. What is the difference between static and kinetic friction?

   1. Static friction occurs when two surfaces are in contact but not moving relative to each other.

   2. Kinetic friction occurs when two surfaces are in contact and moving relative to each other.

7. How can you calculate the coefficient of static friction using the Force Platform Method and the Incline Plane Method, and what are some sources of error associated with each method?

   1. The Force Platform Method involves measuring the minimum force required to start an object moving on a horizontal surface.

   2. The Incline Plane Method involves measuring the angle at which an object just starts to slide down an inclined plane.

   3. Sources of error for the Force Platform Method include air resistance and variations in the surface of the object and the platform. Sources of error for the Incline Plane Method include variations in the angle of the incline and variations in the surface of the object and the incline.

8. How do weight and surface affect the coefficient of static friction?

   1. The coefficient of static friction is higher for heavier objects and for rougher surfaces.

9. How can you design a research project to calculate the coefficient of static friction?

   1. To design a research project to calculate the coefficient of static friction, you would need to identify the materials and equipment you will use, the method you will use to measure the coefficient of static friction, and any sources of error that could affect your results.

10. What is the standard model of friction (ideal friction curve)?

    1. The ideal friction curve shows the relationship between the force of friction and the normal force for a given set of materials.

11. How can you locate and draw normal and frictional forces from a photograph of a sporting activity, and what purpose do these forces serve?

    1. To locate and draw normal and frictional forces from a photograph of a sporting activity, you must identify the surfaces in contact and the direction of motion.

    2. Normal forces serve to keep the object from sinking into the surface, while frictional forces serve to oppose the motion of the object.

12. How can you compute the variables associated with friction, such as the coefficient of friction, normal force, and force of friction?

    1. To compute the variables associated with friction, such as the coefficient of friction, normal force, and force of friction, you would typically need to perform experiments or use equations based on physical laws. Here are some steps and equations that may be useful:

       1. Determine the surface materials: Identify the two surfaces that are in contact and determine their properties, such as their roughness, texture, and chemical composition.

       2. Measure the normal force: The normal force is the force exerted perpendicular to the surface, and it affects the frictional force. You can measure the normal force using a force sensor or by calculating it based on the weight of the object and the angle of the surface.

       3. Measure the force of friction: The force of friction is the force that opposes motion between two surfaces in contact. You can measure the force of friction using a force sensor or by calculating it based on the weight of the object, the angle of the surface, and the coefficient of friction.

       4. Calculate the coefficient of friction: The coefficient of friction is a dimensionless quantity that describes the friction between two surfaces. It is defined as the ratio of the force of friction to the normal force. The equation is: Coefficient of friction = Force of friction / Normal force

       5. Repeat the measurements: To improve the accuracy of the results, you should repeat the measurements multiple times and take the average.

       6. Analyze the results: After obtaining the values for the normal force, force of friction, and coefficient of friction, you can analyze the data to draw conclusions about the frictional properties of the surfaces.

Moments of Force

1. Definition of Moment of Force

   1. Moment of force is the tendency of a force to cause rotation about an axis or a point.

2. (De)stabilizing component and turning component of a muscular force

   1. The destabilizing component of a muscular force refers to the component that tends to destabilize or cause a movement in a direction opposite to that intended.

   2. The turning component of a muscular force refers to the component that produces a rotational force or torque about a joint.

3. Calculation of Moments of Force and Other Variables

   1. Moments of force can be calculated via direct or inverse dynamics.

   2. Direct dynamics calculates the resulting joint torques and accelerations from known joint angles and angular velocities, while inverse dynamics calculates the required joint torques to produce the observed joint accelerations and motions.

   3. Muscle forces, joint angles, joint angular velocities, and joint accelerations are other variables associated with moments of force.

   4. Modifying one variable affects the other variables in the equation, such as an increase in muscle force results in an increase in the moment of force produced by that muscle.

4. Calculation of Centre of Gravity

   1. The centre of gravity is the point in the body around which the mass is equally distributed.

   2. The reaction board method can be used to calculate the centre of gravity of a person by suspending the person on a board and measuring the position of the support points.

   3. The centre of gravity changes with varying body positions.

5. Limitations and Precision of the Centre of Gravity Board Method

   1. The centre of gravity board method has limitations as it only considers the body in a static position and does not take into account the changes that occur during movement or with varying body shapes.

   2. The precision of the centre of gravity board method can be affected by the size and shape of the board, the location and size of the support points, and the accuracy of the measurements.

6. Types of Levers and Their Parts

   1. The three types of levers are first-class levers, second-class levers, and third-class levers.

   2. The parts of a lever include the lever arm, fulcrum, and load.

   3. In a first-class lever, the fulcrum is between the effort and the load.

   4. In a second-class lever, the load is between the effort and the fulcrum.

   5. In a third-class lever, the effort is between the load and the fulcrum.

7. Identification of Levers in the Human Body and in Activities/Tasks

   1. Examples of first-class levers in the human body include the triceps brachii muscle acting at the elbow joint and the sternocleidomastoid muscle acting at the atlanto-occipital joint.

   2. Examples of second-class levers in the human body include the gastrocnemius muscle acting at the ankle joint and the masseter muscle acting at the temporomandibular joint.

   3. Examples of third-class levers in the human body include the biceps brachii muscle acting at the elbow joint and the tibialis anterior muscle acting at the ankle joint.

   4. Levers are used in various activities and tasks, such as in sports equipment like a baseball bat or a diving board.

8. Calculation of Mechanical Advantage and Understanding its Factors

   1. Mechanical advantage is the ratio of the load arm to the effort arm.

   2. A first-class lever can have a mechanical advantage greater than, equal to, or less than one depending on the position of the fulcrum.

   3. A second-class lever always has a mechanical advantage greater than one.

   4. A third-class lever always has a mechanical advantage less than one.

   5. The factors gained or reduced with each type of advantage depend on the type of lever and the direction of the force.