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n South African Journal of Sports Medicine - Mountain-bike racing - the influence of prior glycogen-reducing exercise and glutamine supplementation on selected stress and immune parameters : original research article
Objective. To investigate the effect of pre-exercise glutamine supplementation and the influence of a prior acute bout of glycogen-reducing exercise on the general stress and immune response to acute high-intensity cycling.
Design. Randomised, double-blind, cross-over supplementation study.
Setting and intervention. Subjects performed a series of 4 simulated mountain-bike races lasting ≈ 60 minutes each on separate days 1 week apart, with / without prior glycogen- reducing exercise on a known outdoor course with / without pre-exercise glutamine supplementation. Blood samples were collected pre- and immediately post-exercise after each race.
Main outcome measures. Circulating concentrations of cortisol (COR) and dehydroepiandrosterone-sulphate (DHEAS) were assessed at all time points, as well as changes in white blood cell (WBC) subpopulation distribution.
Results. COR was elevated in all groups post-exercise (p < 0.0001), but neither glycogen reduction, nor glutamine supplementation had any effect. DHEAS increased post-exercise (p < 0.05), with a greater relative increase in glutamine-supplemented subjects (p = 0.07). Total WBC and neutrophil counts in all groups were elevated after exercise (both p < 0.0005). Glutamine supplementation had no effect on differential WBC counts or distribution, but total WBC (p = 0.06) and monocyte (p < 0.05) counts showed greater increases after glycogen reduction. Gluta-mine supplementation was associated with greater postexercise decreases in CD4+ count (p = 0.07) and CD4+: CD8+ ratio (p = 0.01) after glycogen-reducing exercise.
Conclusions. We conclude that pre-exercise glutamine supplementation may have an anticortisol effect by enhancing the DHEAS response to exercise stress. The suppressive effect of glutamine supplementation on CD4+: CD8+ ratio and its positive effect on monocyte count after repeated bouts of exercise warrants further investigation.
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