Influence Of Carbohydrate/placebo On Oxidative Changes And Plasma Antioxidant Capacity Following 2.5-hours Of Intensive Cycling

Abstract

Carbohydrate administration during exercise has been shown to diminish cortisol and catecholamine hormone release. These hormones may mediate oxidative stress, but this relationship has not been examined during cycling exercise. Purpose The purpose of this project was to study the effect of carbohydrate (CHO) compared to placebo (PLA) ingestion on oxidative stress following 2.5 hours of intensive cycling in 15 highly trained cyclists compared to 5 resting controls. Methods Subjects were recruited and five control subjects (non-exercise) were utilized to control for time and lab drift effects. Subjects agreed to avoid the use of large-dose vitamin/mineral supplements (above 100% of recommended dietary allowances) for one week prior to each test session. Subjects functioned as their own controls and ingested CHO or PLA beverage in a randomized, counterbalanced design. Subjects reported to the lab at 3:00 pm not having ingested energy for at least 5 hours. The two cycling bouts (75% VO2max) were 4–6 weeks apart. Subjects received CHO or PLA beverages 15–30 min pre-exercise (12 ml/kg) and during the 2.5-h cycling bout (4 ml.kg−1.15 min−1). Blood and skeletal muscle biopsy samples were collected 30 min pre-exercise, immediately post-exercise, and 12-h post-exercise and analyzed for F2-isoprostanes, ferric reducing ability of plasma (FRAP), cortisol, and epinephrine and muscle glycogen, respectively. The statistical design was a 2 (treatment) × 3 (time) repeated measures ANOVA. Results The pattern of change between groups was significant for the increase in F2-isoprostanes, cortisol, and epinephrine (P = 0.004, P = 0.012, and P = 0.02, respectively) indicating that CHO vs PLA resulted in diminished increases of these compounds. Although significant time effects were found for the increase in FRAP (P = 0.000) and the decrease in muscle glycogen (P = 0.000), interaction effects were not significant. Significant correlations were found between cortisol, muscle glycogen, FRAP, epinephrine, and F2-isoprostanes. Conclusion These findings indicate that oxidative stress during cycling exercise is influenced by stress hormones, muscle glycogen content, and plasma antioxidant potential. Supported by a grant from Gatorade.