Eccentric exercise-induced muscle damage impairs muscle glycogen repletion

Abstract

Five healthy untrained young male subjects were studied before, immediately after, and 10 days after a 45-min bout of eccentric exercise on a cycle ergometer (201 W). The subjects were sedentary at all other times and consumed a eucaloric meat-free diet. Needle biopsies of the vastus lateralis muscle were examined for intracellular damage and glycogen content. Immediately after exercise, muscle samples showed myofibrillar tearing and edema. At 10 days, there was myofibrillar necrosis, inflammatory cell infiltration, and no evidence of myofibrillar regeneration. Glycogen utilization during the exercise bout was 33 mmol glycosyl units/kg muscle, consistent with the metabolic intensity of 44% of maximal O2 uptake; however, the significant glycogen use by type II fibers contrasted with concentric exercise performed at this intensity. At 10 days after exercise, muscle glycogen was still depleted, in both type I and II fibers. It is possible that the alterations in muscle ultrastructures were related to the lack of repletion of muscle glycogen. Damage produced by eccentric exercise was more persistent than previously reported, indicating that more than 10 days may be necessary for recovery of muscle ultrastructure and carbohydrate reserves.

Metabolic Consequences of Exercise-Induced Muscle Damage

“…In contrast to both of these hypotheses, an earlier study by O'Reilly et al (1987) [14] failed to show selective glycogen repletion in either muscle fibre type following eccentric exercise. The exercise protocol used involved untrained subjects performing an eccentric cycling bout.…”

“…This initial disruption is followed by degeneration during which the damaged myofibrillar proteins are acted on by proteases. A number of studies have reported the infiltration of immune cells within 2 to 3 days following injury [14,17] , but other researchers have failed to show an immune response [2,10,20] . Regeneration follows with satellite cells becoming centrally located and replacing the damaged myofibrils.…”

“…However, a number of studies have shown muscle glycogen synthesis to be impaired following eccentric exercise resulting in EIMD [2][3][4]6,14,17,18,20] . Some studies have even shown muscle glycogen concentrations to be lower 24-48 hours later compared to immediately after the completion of the exercise bout [48] , suggesting the complete inhibition of glycogen synthesis.…”

“…Researchers have used a number of eccentric exercise models to induce and study EIMD. A rather artificial method of inducing EIMD has been the use of protocols in which the exercise component is purely eccentric; these protocols involve resisting the action of a weight or lever [2,4,6] , as in eccentric cycling [7,14] . Other protocols have combined concentric and eccentric actions but placed the greater emphasis on the eccentric component.…”

Repeated muscle damage blunts the increase in heat strain during subsequent exercise heat stress

“…EIMD has also been shown to inhibit glycogen resynthesis (O'Reilly et al 1987), yet altered metabolism is also an unlikely mechanism since RER was not different between EIMD trials. Whilst there was no effect on Tsk, we did observe a lower temperature threshold for sweating onset, and a lower thermal sensation during HS on the second EIMD bout.…”