Question

what happens when a muscle is fatigued?
it is unable to contract efficiently due to a depletion of atp.
it is unable to contract efficiently due to a buildup of atp.
it becomes stronger due to increased blood flow.
it contracts more efficiently due to an increase in atp.
it becomes less flexible due to increased blood flow.

Explanation:

ATP is the energy - currency for muscle contractions. When a muscle is fatigued, its ATP stores are depleted, hindering efficient contraction. Increased blood flow doesn't make a fatigued muscle stronger or less flexible in the context of fatigue. Buildup or increase in ATP doesn't occur during fatigue.

Answer:

It is unable to contract efficiently due to a depletion of ATP.