Creatine and acute hypohydration: Effect on plasma volume, mineral, and electrolyte balance
Creatine (Cr) is a widely used dietary supplement that has been demonstrated to enhance muscular strength and anaerobic power. However, coaches, trainers, professional sports teams, and physicians have raised concerns regarding its safety. They are especially concerned with numerous anecdotal reports suggesting that Cr supplementation compromises an individual's heat tolerance during exercise, subsequently leading to an increase of skeletal muscle cramping and tearing. The purpose of this study was to investigate the effects of oral Cr supplementation and acute hypohydration on plasma volume, electrolyte and mineral balance, and anaerobic exercise performance. Using a randomized double-blind design, 15 subjects ingested either 20 g·d -1 of creatine monohydrate (CR) (n = 8) or a placebo (PL) (n = 7) for 5-d and then undertook two consecutive 80-min hypohydration protocols resulting in ∼1.5% (D1) and ∼3% (D2) decreases in body mass (BM). After 5-d of supplementation there was a significant increase in BM in both groups (PL: 0.6 ± 0.5; CR: 1.5 ± 0.1 kg), but there was no difference between groups (P = 0.09). There were no significant changes in body composition, plasma volume (ΔPV), serum electrolytes (Na, K, Cl), minerals (Mg, Zn, Ca), osmolality, or anaerobic exercise performance measures of maximum power (MP), total work (TW), or fatigue index (FI) as determined from ten, 6-s sprints on a cycle ergometer. As expected, the two 80-min hypohydration sessions resulted in a significant ΔPV in both groups at D1 (PL: -10.9 ± 2.0; CR: -9.2 ± 1.6%) and D2 (PL: -15.6 ± 2.1; CR: -16.5 ± 1.6%) but no difference between groups. There were no significant differences between groups at either D1 or D2 for measures of serum electrolytes, minerals, osmolality, MP, TW, or FI. This is the first reported study investigating Cr supplementation and hypohydration. Recognizing the limitation of the small sample size used in this study, the results suggest that a 5-d loading dose of Cr does not negatively affect plasma volume or serum electrolyte and mineral balance. However, neither does it appear to enhance the performance of repeated bouts of anaerobic exercise.