A researcher is measuring the oxygen consumption of subjects while they are seated and performing 5 repetitions of concentric isotonic contractions at the rate of 0.5/second on an isolated muscle, the biceps brachii, loaded with 33% of the minimum isometric load. On the next day, the same subjects are required to perform 50 contractions at the same rate with the same load. What is likely to be different about the sarcomere functions during the second-day trials?

a. Greater power output
b. Higher cellular ATP/ADP ratio
c. Less oxygen consumption per second
d. More calcium release
e. Slower cross-bridge cycling

c. Less oxygen consumption per second

Explanation:

The sarcomere is a functional unit of muscle tissue. During repeated muscle contractions, the oxygen delivery to the muscle is reduced. As noted in the question, the rate and load of muscle contractions are the same under both conditions but the differences in the number of contractions in the second day experiment only increase. So as the number of contractions increases, more time is required to work. But continuous work can lead to a shortage of oxygen. Therefore, due to low availability, less oxygen per second is consumed. Lactic acid production by anaerobic respiration through muscle tissue causes muscle fatigue. Considering other dubious options, there is no increase in load and there is not much power generation. At the same time, ATP consumption increases due to continuous contraction, so the cellular ATP / ADP ratio is generally reduced. Since the calcium release by the sarcomere is reduced during continuous muscle contraction and the contraction rate does not change, the cross-bridge cycling speed is not affected.

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