Relation of Induced Anoxemia to the Pain of Muscular Exercise. 20

Exercise of the forearm during the time that the arterial blood oxygen is progressively lowered will initiate pain in the exercised muscles. The pain disappears when the blood is suddenly saturated with oxygen although the exercise be continued. If the same exercise is performed at the same rate while the arterial blood remains saturated with oxygen, no pain appears. Increasing the frequency of the exercise may cause pain to appear even when the blood is saturated with oxygen. Decreasing the frequency of exercise while maintaining the arterial oxygen at a low level may result in no pain.

This work can be correlated with the reports of MacWilliam and Webster 1 and of Lewis, Pickering, and Rothschild, 2 who found that exercise of a muscle that had been made ischemic, results in pain. Their work showed that inadequate blood supply to a working muscle causes pain. In my experiments the blood supply, save for the lowered oxygen content, was unaltered in composition, yet pain appeared during exercise. This shows that oxygen want is the the chief contributing cause of pain developing in an exercised muscle. It is, therefore, suggested that the cause of pain in muscular exercise is the incomplete oxidation of the products of muscle metabolism. The same process may be responsible for the pain of angina pectoris (Rothschild and Kissin 3 ) and of intermittent claudication.