CSCS CSCS: Biomechanics of Resistance 4 — Questions and Answers
Question 1: The angle of pennation in a pennate muscle affects force production primarily by influencing which variable?
- Cross-sectional area contribution to resultant force (Correct answer)
- Maximum shortening velocity
- Muscle moment arm length
- Fiber recruitment threshold
Correct answer: Cross-sectional area contribution to resultant force
As pennation angle increases, a larger fraction of fiber force is directed along the muscle's line of action, affecting the effective force transmitted to the tendon.
Question 2: During an Olympic clean, the barbell transitions from the first to the second pull. The primary biomechanical change is:
- Increased knee flexion and reduced hip extension velocity
- Rapid triple extension of ankle, knee, and hip to accelerate the barbell (Correct answer)
- Decreased ground reaction force as the lifter rises to toes
- Anterior shift of the center of mass behind the base of support
Correct answer: Rapid triple extension of ankle, knee, and hip to accelerate the barbell
The second pull is characterized by explosive triple extension (ankle, knee, hip) to generate maximum barbell velocity before the catch phase.
Question 3: Which factor primarily determines the length of a muscle's moment arm?
- The physiological cross-sectional area of the muscle
- The perpendicular distance from the muscle's line of action to the joint axis (Correct answer)
- The number of motor units activated
- The ratio of fast-twitch to slow-twitch fibers
Correct answer: The perpendicular distance from the muscle's line of action to the joint axis
The moment arm is the perpendicular distance from the joint axis of rotation to the muscle's line of action, and it determines how efficiently force creates torque.
Question 4: A force of 200 N is applied to a dumbbell 0.3 m from the elbow joint axis. What is the torque produced?
- 60 N·m (Correct answer)
- 667 N·m
- 0.0015 N·m
- 200.3 N·m
Correct answer: 60 N·m
Torque = Force × Moment arm = 200 N × 0.3 m = 60 N·m.
Question 5: In biomechanics, 'impulse' is defined as:
- Force multiplied by displacement
- Change in velocity divided by time
- Force multiplied by time (Correct answer)
- Mass multiplied by acceleration
Correct answer: Force multiplied by time
Impulse equals force × time (J = F × Δt) and equals the change in momentum of an object, per the impulse-momentum theorem.
Question 6: Which of the following best describes 'valgus collapse' at the knee and its primary biomechanical risk?
- Excessive knee hyperextension increasing ACL tensile stress
- Combined knee adduction and tibial external rotation increasing ACL strain
- Patella alta causing reduced patellofemoral contact area
- Combined knee abduction and tibial internal rotation increasing ACL strain (Correct answer)
Correct answer: Combined knee abduction and tibial internal rotation increasing ACL strain
Dynamic valgus collapse involves knee abduction with tibial internal rotation, placing the ACL under high tensile stress and increasing non-contact injury risk.
Question 7: Which concept explains why a longer limb segment generally requires more muscle torque to accelerate than a shorter segment of equal mass?
- The longer segment has greater linear velocity
- The longer segment has a higher moment of inertia (Correct answer)
- The longer segment stores more elastic energy
- The longer segment reduces the center of gravity
Correct answer: The longer segment has a higher moment of inertia
Moment of inertia increases with the square of the radius of gyration; a longer segment has mass distributed farther from the rotation axis, requiring more torque to accelerate.
CSCS CSCS: Biomechanics of Resistance 4
The angle of pennation in a pennate muscle affects force production primarily by influencing which variable?