Question 25

Adding more motor units increases the strength of a muscle contraction.

Recruiting additional motor units enhances the force of muscle contractions. This process allows for a greater number of muscle fibers to be activated simultaneously, leading to a stronger overall contraction.

A) Moving the actin at a faster rate

While increasing the speed of actin movement can affect the rate of contraction, it does not directly contribute to the overall strength of a muscle contraction. The strength is primarily determined by the number of motor units engaged rather than the speed at which actin filaments slide.

B) Reducing the number of sarcomeres

Reducing the number of sarcomeres would decrease the muscle’s ability to generate force. Sarcomeres are the fundamental units of muscle contraction, and fewer sarcomeres mean less capacity for muscle contraction strength.

C) Adding more motor units

This option is correct as it directly correlates with increasing the strength of muscle contractions. Engaging more motor units allows more muscle fibers to be activated, resulting in a more powerful contraction.

D) Slowing down the myosin fibers

Slowing down myosin activity would likely reduce the speed of contraction, which does not contribute to an increase in contraction strength. The strength of a contraction is more about the recruitment of muscle fibers rather than the speed of the myosin heads.

Conclusion

Adding more motor units is the definitive action that increases muscle contraction strength, as it enhances the recruitment of muscle fibers. Other options either do not contribute to strength or would diminish the muscle's capacity to generate force. Therefore, option C is the clear choice for maximizing muscle contraction strength.