Effects of load and duration of tension on pain induced by muscular contraction

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Abstract
Pain was induced in the ischemic forearm in more than 300 tests in seven subjects by an exercise which consisted of compression of an air bulb to raise or maintain a mercury column at 50, 100, or 200 mm for periods of 1, 2, 4, or 5.5 sec. The rate of pain development could be correlated with the product (P) of the number of contractions, square root of the load (in mm Hg), and cube root of the duration of contraction (in sec). Slight pain appeared at a product of about 345 P, moderate pain at approximately 433 P, severe pain at 536 P, and intolerable pain at 626 P. A similar relationship could be shown in maintained contraction provided the total duration was treated as if each 5.5 sec of the maintained contraction constituted a separate contraction. Ischemia of the arm for periods up to 15 min had no effect on product. Recovery from the effect of exercise was complete in 10 min. Simultaneous exercise of the other arm had no effect on the rate of pain development. The results support the concept that muscle pain results from the local accumulation of a slowly diffusible material released during muscle contraction.