Final answer:
The force produced by skeletal muscles can be increased by decreasing the interval between contractions, which facilitates summation of twitches and leads to a stronger contraction through sustained calcium ion presence in the sarcoplasm. The correct option is d.
Step-by-step explanation:
The question revolves around how to increase the force produced by a skeletal muscle. When a muscle fiber receives an action potential from a controlling neuron, it contracts. For a muscle to produce maximal power, the overlap between thin and thick filaments needs to be optimal, within a muscle's active range.
Increasing the frequency of action potentials can indeed increase the force, as repeated signals ensure that more calcium is available in the sarcoplasm to bind to troponin and displace tropomyosin, exposing the actin binding sites.
Hence, increasing the interval between contractions (choice d) would have the opposite effect of what is desired. Excitation-contraction coupling refers to this sequence of events, where the action potential triggers the release of calcium from the sarcoplasmic reticulum (SR).
Tetanus, or the sustained contraction of muscle fibers, occurs when calcium ion concentration in the sarcoplasm allows for continuous cross-bridge formation, maintaining muscle tension. Shortening the interval between twitches can lead to summation and eventually tetanus.
Therefore, the correct way to increase muscle force would be by decreasing the interval between contractions (option d), which allows for the summing of individual twitches into a more sustained and stronger muscle contraction.