Muscle damage and soreness following prolonged intermittent shuttle running and the effect of vitamin C supplementation
Exercise-induced muscle soreness and damage have been investigated for almost a century, and yet it appears that there is little that can be done to avoid these consequences of over-exertion, except train on a regular basis. It is likely that freeradicals are involved at a number of stages in the muscle damage process, and therefore the provision of appropriate antioxidants may theoretically offer some protection. One such antioxidant is vitamin C, although the literature available in support of this notion is scarce. The aim of these studies, therefore, was to assess whether different nutritional interventions using vitamin C would offer any benefit to exercise-induced muscle damage and soreness. In the past, investigators have often used exercise protocols designed to maximise the extent of injury. The studies reported in this thesis, however, used an exercise protocol (Loughborough Intermittent Shuttle Test: LIST) based on the multiple-sprint sports (e.g. football). Participation in such sports is very high, although frequently on an irregular basis, and therefore exercise of this nature may have the capacity to cause muscle damage and soreness. The LIST provided a suitable exercise model, and in different studies led to increases in soreness, markers of muscle damage, lipid peroxidation, and inflammation. It also led to poorer muscle function up to 72 h after exercise in some muscle groups. Short-term supplementation with vitamin C 2 hours before exercise successfully increased plasma and cellular concentrations, although failed to have any beneficial outcomes in terms of muscle damage or soreness. Supplementation in the hours and days (up to three days) after exercise also produced no beneficial effects, and it may be that supplementation occurred at an inappropriate time. Prolonged supplementation with vitamin C proved more promising (14 days), and was associated with reduced plasma concentrations of interleukin-6 and malondialdehyde. Furthermore, there were modest benefits to certain' aspects of muscle soreness and function, although these were not always statistically significant. However, tliere was no effect on circulating markers of muscle damage (creatine kinase and myoglobin). These findings suggest that the regular ingestion of vitamin C may be associated with some favourable changes following damaging exercise. However, the consumption of large amounts of vitamin C immediately before or after exercise offer no appreciable benefits, despite large changes in plasma concentrations of this vitamin.