Influence of Carbohydrate/Placebo On Immunity Following 2-h Cycling With or Without Rest Intervals

Abstract

PURPOSE: The purpose of this project was to study the effect of carbohydrate compared to placebo ingestion on immune changes following 2 hours of intensive cycling with or without rest intervals. METHODS: Trained cyclists (N=12) functioned as their own controls during four test sessions that were separated by 1–2 weeks and randomized to control for an order effect. Subjects cycled for 2.0 h at ∼60% Wattsmax continuously (C) or with 3-min rest intervals (R) interspersed every 10 min (2.6 h total time) while receiving 4 ml kg−1.15 min-1 carbohydrate (6%) (Cho) or placebo (Pla) beverages (thus CCho, CPla, RCho, RPla). Blood samples were collected 30 min pre-exercise, and immediately and 1-h post-exercise. Immune and hormonal measures included determination of leukocyte subset counts, plasma IL-6, IL-10, IL-1ra, IL-8, cortisol, glucose, and insulin, PHA-induced lymphocyte proliferation, and natural killer cell activity (NKCA). Blood leukocyte relative gene expression was measured for four cytokines (IL-6, IL-8, IL-10, IL-1ra) using real-time quantitative RT-PCR. RESULTS: Exercise-induced immune and hormonal changes did not differ between C and R trials. Cho compared to Pla ingestion attenuated exercise-induced changes in blood neutrophil, monocyte, T cell, and NK cell counts, plasma cortisol and insulin, plasma IL-6, IL-10, and IL-1ra, and PHA-induced lymphocyte proliferation, but not NKCA (interaction effect, P=0.134). Significant time effects were measured for leukocyte IL-10 (increase), IL-1ra (increase), and IL-6 (decrease) mRNA content with no significant differences measured when comparing C or R exercise modes or Cho and Pla test conditions. The patterns of change in leukocyte IL-8 mRNA did not differ between Cho and Pla, but increased during C and decreased during R exercise trials (exercise mode × time interaction effect, p < 0.001). CONCLUSIONS: Most measured immune and hormonal changes induced by intense and prolonged exercise were attenuated when cyclists ingested Cho compared to Pla beverages, but were largely unaffected when athletes were allowed to rest 3 min every 10 min of exercise.