CARBOHYDRATE SUPPLEMENTATION IMPROVES PERFORMANCE DURING HIGH-INTENSITY INTERMITTENT EXERCISE IN THE HEAT

Abstract

23 Carbohydrate (CHO) supplementation during exercise has been shown to improve endurance performance during continuous mild-intensity exercise(>90 min). Only a few CHO supplement protocols involve intermittent exercise or gender comparisons, and even less have been conducted in the heat. Thus, the purpose of this study was to compare an 8% CHO supplement vs. an artificially sweetened placebo (P) during intermittent high-intensity exercise in the heat (35 °C, 50% rh). Sixteen (8M, 8F) moderately trained subjects cycled at 80% of their VO2 max at a 1 min. work/1 min. rest ratio, drinking (2.5 ml/kg) every 15 min. A trial was two 45 min. sessions, with a 10 min. rest between. A trial ended when a subject failed to maintain cycle cadence, HR reached 180 bpm, or core body temperature (Tc) reached 39.5°C. In double blind fashion, subjects attempted two trials one month apart to control for menstrual cycle Tc fluctuations. Results showed that the CHO drink significantly increased time to exhaustion (CHO=88.1 min, P=85.2 min, p=.05). Male subjects lasted 2.4% longer in the CHO trial, and females exercised 4.1% longer. The majority of the trials were terminated by high Tc. During the CHO trial, Tc rose at a rate of 1.25 °C/hr, while the rise was 1.38 °C/hr during the P trial. Pre-Post blood glucose increased significantly in the CHO trial (4.1 to 5.6 mg/dl), while in the P trial, pre and post blood glucose were identical (4.3 mg/dl). Post-test blood lactate was significantly higher in the CHO trial (3.3 mg/dl) then the P ride(2.6 mg/dl). These findings indicate that fluid with added CHO may synergistically improve performance and heat tolerance during high intensity intermittent exercise, possibly due to a reduction in the rise of Tc during exercise.