During intense exercise, your muscles build up relatively large concentrations o

Question

During intense exercise, your muscles build up relatively large concentrations of lactic acid. What effect might this build-up of lactic acid have on muscle contraction rate?
a) Muscle contraction rate would increase because a lower pH
would decrease the activity of AChE.
b) Muscle contraction rate would decrease because a lower pH
would increase the activity of AChE.
c) Muscle contraction rate would decrease because lactic acid
would competitively bind with ACh.
d) Muscle contraction rate would increase because a reduced
pH makes ACh more rapidly catalyze the reaction necessary
for muscular contraction.

Explanation / Answer

As our bodies perform strenuous exercise, we begin to breathe faster as we attempt to shuttle more oxygen to our working muscles. The body prefers to generate most of its energy using aerobic methods, meaning with oxygen. Some circumstances, however, --such as evading the historical saber tooth tiger or lifting heavy weights--require energy production faster than our bodies can adequately deliver oxygen. In those cases, the working muscles generate energy anaerobically. This energy comes from glucose through a process called glycolysis, in which glucose is broken down or metabolized into a substance called pyruvate through a series of steps. When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown--and thus energy production--to continue. The working muscle cells can continue this type of anaerobic energy production at high rates for one to three minutes, during which time lactate can accumulate to high levels.

so the answer is

d) Muscle contraction rate would increase because a reduced pH makes ACh more rapidly catalyze the reaction necessary for muscular contraction.

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