Question
The diagram below shows the force-velocity relationship for isotonic contractions of skeletal muscle. The differences in the three curves result from differences in which of the following?
| A. |
Frequency of muscle contraction |
| B. |
Muscle mass |
| C. |
Myosin ATPase activity |
| D. |
Recruitment of motor units |
Show Answer
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Correct Answer � C Explanation |
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Ans. C. Myosin ATPase activity.
- The diagram shows that the maximum velocity of shortening (V-Max) occurs when there is no afterload on the muscle (force = 0).
- Increasing afterload decreases the velocity of shortening until a point is reached where shortening does not occur (isometric contraction) and contraction velocity is thus 0 (where curves intersect X-axis).
- The maximum velocity of shortening is dictated by the ATPase activity of the muscle, increasing to high levels when the ATPase activity is elevated.
- Choice A: Increasing the frequency of muscle contraction will increase the load that a muscle can lift within the limits of the muscle, but will not affect the velocity of contraction.
- Choices B and D: increasing muscle mass, and recruiting additional motor units will increase the maximum load that a muscle can lift, but these will not affect the maximum velocity of contraction.