Which on:off time ratio in functional electrical stimulation would lead to the most rapid onset of muscle fatigue?

The correct answer is related to the on:off time ratio used in functional electrical stimulation and its effect on muscle fatigue. An on:off time ratio of 5:1 means that for every 5 parts of time the muscle is stimulated (on), there is 1 part of time for rest (off).

This longer stimulation period allows for a higher frequency of contractions but gives the muscle less recovery time relative to its contraction time. As a result, the muscle can become fatigued more quickly due to the accumulation of metabolic byproducts and the depletion of energy substrates. The more pronounced the stimulation compared to the rest, the less time there is for the muscle fibers to recover between contractions, leading to quicker fatigue.

In contrast, ratios with a larger off time relative to on time, such as 1:4 or 1:6, provide the muscle ample recovery time, leading to a lower risk of fatigue. Therefore, the 5:1 ratio is more likely to result in rapid muscle fatigue compared to the other ratios presented.