| Summary: | Two types of dynamic muscle contractions have been compared to investigate their effects on muscle pain and damage in normal subjects. Damage was assessed by studying changes in isometric force generation, muscle enzyme loss, morphological changes and the patterns of radioisotope uptake.
Delayed onset muscle pain occurred after eccentric but not concentric contractions and was associated with appreciable muscle damage.
A technique was developed to quantitate the intensity and distribution of tenderness in superficial muscles. It was reproducible and showed the bellies as well as attachments to be affected. No discomfort was experienced for approximately eight hours after exercise, and was maximal 1-2 days later.
Dissimilar time courses emerged for the various indicators of damage; impairments of force generation were greatest immediately after exercise and had largely recovered 24 hours later. Small localised areas of morphological damage were seen immediately after exercise, and were more extensive 2-3 days later.
Some subjects had an unexpectedly large and delayed rise in plasma muscle enzyme levels which increased for 3-6 days. This slow time course paralled the muscle uptake of radioisotope and both imply damaged muscle membranes. The use of radioisotopic techniques showed that increased uptake did not occur in all painful muscles, and thus membrane damage is not the pain stimulus. Morphological changes best approximated, but did not exactly follow, the time course of pain and tenderness.
Both pain and enzyme efflux respond rapidly to training, in the absence of isometric strength changes. The intensity of exercise and the amount of lengthening seemed to be the critical factors in causing damage.
It is concluded that the pain and damage are initiated by high mechanical tensions, but the algesic stimulus remains unclear. These results question the use of intensive eccentric contractions in training and rehabilitation programmes.
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