Thermoregulatory Changes During 30 Days Of Creatine Supplementation While Exercising In The Heat

Abstract

PURPOSE: The purpose of this investigation was to determine the effects of 30 d of creatine supplementation (20g/d for 7 d followed by 6g/d for 23 d) on thermoregulation in the heat (temp 33.06 + 0.58oC; hum 21.42 + 3.02%). Specifically the investigation determined thermoregulation in the heat at 7 d intervals while engaged in a common creatine supplementation protocol. METHODS: Twelve males (age = 21.13 + 1.54 yrs; ht = 172.92 + 8.43 cm; wt = 80.52 + 10.35 kg) participated in a total of 10 exercise sessions (5 Cr supplementation; 5 Pl). Exercise sessions consisted of running at 65-70% VO2max for 45 min in the heat at 7 d intervals over a 30 d supplementation period. Measures of thermoregulation, hydration, and body water were performed at each exercise session and included: pre-exercise total body water (TBW), extracellular water (ECW), and intracellular water (ICW); pre/post-exercise changes in nude body weight (NBW), and urine specific gravity (USG); during exercise changes in core temperature (Tc) and plasma volume (PV). The order of testing sessions were: day 0 baseline, test session 1; day 7 test session 2; day 14 test session 3; day 21 test session 4; day 28 test session 5. RESULTS: There were no significant differences in ECW and ICW between creatine and placebo over the 30 d supplementation. TBW resulted in a significant interaction. TBW for creatine was less at pre-supplementation versus days 14 and 21 (pre = 48.49 + 1.66 L; day 14 = 49.92 + 1.52 L; day 21 = 49.80 + 1.41 L) and day 7 TBW was less than day 21 (day 7 = 48.67 + 1.34 L; day 21 = 49.92 + 1.52 L). For placebo, day 14 TBW was greater than day 30 (day 14 = 48.99 + 1.43 L; day 30 = 48.13 + 1.39 L). Creatine had significantly lower USG versus placebo (Cr = 1.015 + 0.003; Pl = 1.020 + 0.002) at day 21. There were no differences between creatine and placebo for Tc and PV. Tc however resulted in a significant time effect with Tc increasing throughout the exercise session for both creatine and placebo. CONCLUSIONS: Creatine supplementation had no effect on thermoregulation versus placebo while exercising in the heat. The changes in TBW and USG at 21 days for the creatine condition suggest that TBW increases continue to appear with creatine supplementation and that those changes may not be of significant magnitude to positively affect thermoregulation while exercising in the heat.