Exercise-Induced Muscle Damage and Adaptation

Abstract

Novel, unaccustomed exercise has been shown to result in temporary, repairable skeletal muscle damage. After exhaustive endurance exercise, muscle damage can be produced by metabolic disturbances associated with ischaemia. Extensive disruption of muscle fibres also occurs after relatively short term eccentric exercise where high mechanical forces are generated. Biopsies taken after repetitive eccentric muscle actions have revealed broadening, streaming and, at times, total disruption of Z-discs. Muscles that develop active tension eccentrically also become sore, lose inherent force-producing capability, and show a marked release of muscle proteins into the circulation. Because creatine kinase (CK) is found almost exclusively in muscle tissue, it is the most common plasma marker of muscle damage. Despite the universal use of CK as a marker, several factors with regard to efflux and clearance remain unexplained. Also the large intersubject variability in response to exercise complicates its interpretation. Damage progresses in the postexercise period before tissues are repaired. However, the mechanism to explain exercise-induced muscle damage and repair is not well defined. Among the factors that may influence the damage and repair processes are calcium, lysosomes, connective tissue, free radicals, energy sources, and cytoskeletal and myofibrillar proteins. Physical conditioning results in an adaptation such that all indicators of damage are reduced following repeated bouts of exercise. Recently, investigators have suggested that the prophylactic effect of training may be due to performance of a single initial exercise bout. Following a second bout of exercise performed 1 to 6 weeks after the first bout, there is a reduction in morphological alterations and performance decrements and a profoundly reduced elevation in plasma CK levels. Several hypotheses have been presented to explain the repeated bout or rapid training effect. Stress-susceptible fibres may be eliminated or susceptible areas within a fibre may undergo necrosis and then regenerate. These regenerated fibres, along with adaptations in the connective tissue, may provide greater resistance to further insult.

Aspectos atuais sobre estresse oxidativo, exercícios físicos e suplementação

“…None of these isolated alternatives have shown increase of the defense capacity of the body or reduction of the effects of the aerobic metabolism (11) . However, according to Finkel and Holbrook (12) , the most efficient strategy in increasing the endogenous amount of antioxidants may be a greater induction of the oxidative stress itself, which would gradually stimulate the cellular antioxidant mechanisms and would increase the resistance to injuries induced by exercise (13)(14)(15)(16) . It is worth mentioning that the greatest part of the effects induced by physical exercise (increase of muscular mass, improvement of the cardiovascular system, reduction of the incidence of diseases and infections and others) is mainly due to the adaptations induced over the several body systems, including the endogenous antioxidant system (14,16) .…”

A light load eccentric exercise confers protection against a subsequent bout of more demanding eccentric exercise

“…1 It is known that eccentric exercise produces these symptoms greater than concentric exercise, 2 and the symptoms are often used as markers of muscle damage. 1,3 When eccentric exercise is repeated, the magnitude of changes in the markers is smaller and recovery of muscle function is faster compared to the initial bout. 1,4 This protective effect is often referred to as the repeated bout effect, 1,4 and is known to last for several months for the case of maximal eccentric exercise of the elbow flexors.…”

Muscle plasticity related to changes in tubulin and αB-crystallin levels induced by eccentric contraction in rat skeletal muscles

“…We suggest that the largest mechanical stress seen in this study occurred by eccentric contraction and not by other forms of contraction, and that it efficiently responded to muscular environmental changes, including muscle hypertrophy. It is possible that different responses within the sarcomere produced different results between the soleus muscle and GCM in this study, because the active mechanical force from eccentric contraction was directed to the Z-line of the sarcomere, which is a starting point for various signal cascades associated with muscle plasticity (10).…”