Journal Title (Medline/Pubmed accepted abbreviation): Int J Sports Med
Page number: 659-665
doi : 10.1055/s-0031-1271698
Background: Compared with exercise in thermoneutral conditions, exercise in the heat exacerbates hormonal and immune responses, including reductions in salivary flow and immunoglobulin A (IgA) secretion rates and increased cortisol levels that can inhibit salivary IgA transport. Together, these factors may contribute to higher levels of oral pathogens and an increased risk of upper respiratory infections. Fluid intake, especially if carbohydrates (CHO) are included, may ameliorate these responses, in part, through CHO-mediated attenuation of cortisol response.
Hypothesis/purpose: The purpose of this study was to evaluate the effects of CHO supplementation on salivary IgA and cortisol responses during soccer-specific intermittent exercise in a hot environment.
Subjects: Ten males who regularly participated in physical exercise (3 times/wk) participated in this study (mean age, 26 ± 4 y; height, 1.8 ± 0.05 m; weight, 74.2 ± 5.7 kg; body mass index, 23.4 ± 2 kg/m 2; maximal oxygen consumption [VO2max], 62.6 ± 5.6 mL/kg/min). Salivary responses are based on 8 men.
Experimental design: Randomized, double-blind, cross-over
Treatments Protocol: Participants were randomized to receive an orange-flavored drink containing either 6% (weight/volume) CHO or a sweetener (placebo), with fluid volume based on body mass (3 mL/kg). Participants completed an exercise session with each drink separated by 7 days. Equal portions were drunk at 5 minutes before the exercise and at 15-minute intervals during the 90-minute exercise. Each exercise session consisted of a warm-up (stretching exercises and a 5-min treadmill run) and six 15-minute exercise periods with a 15-minute intermission in the middle at 30° C and 40% relative humidity. Each exercise period represented 5 different exercise categories (standing, walking [4 km/hr], jogging [10 km/hr], cruising [13 km/hr], and sprinting [19 km/hr]). Expired gas volumes were collected every 10 seconds. Heart rate and core body temperature were monitored continuously. Saliva samples for IgA and cortisol levels and calculation of salivary flow rate were collected before exercise and immediately, 24 hours, and 48 hours after exercise. Thermal sensation and rating of perceived exertion (RPE) were recorded every 15 minutes. Gut fullness and thirst levels were recorded before and after drink ingestion before exercise and the intermission period.
In this study, CHO ingestion did not affect the physiologic responses to exercise in the heat. Higher heart rates in the CHO group may have resulted from an initial and progressive state of dehydration in this group compared with the placebo group. It is disconcerting that the results reported for salivary cortisol concentrations reported in Table 2 are opposite of those reported in the text.