During strenuous exercise or physical work,the demand for oxygen increases several fold so that it does not diffuse into skeletal muscle fibers at the rates required by them.

These questions consist of two statements each,printed as Assertion and Reason.While answering these questions you are required to chose any one of the following four responses. If both Assertion and Reason are true and Reason in correct explanation of Assertion. If both assertion and Reason are true but reason is not correct explanation of Assertion. If Assertion is true but Reason is false. If both Assertion and Reason are false. Assertion:During exercise , a person undergoes fatigue very soon. Reason:During this period ,muscle fibres undergo oxygen debt.