Effects of creatine supplementation on the energy cost of muscle contraction: a P-31-MRS study

Five women and 3 men (29.8 +/- 1.4 yr) performed dynamic knee-extension exe rcise inside a magnetic resonance system (means +/- SE). Two trials were pe rformed 7-14 days apart, consisting of a 4- to 5-min exhaustive exercise bo ut. To determine quadriceps cost of contraction, brief static and dynamic c ontractions were performed pre- and postexercise. P-31 spectra were used to determine pH and relative concentrations of P-i, phosphocreatine (PCr), an d beta ATP. Subjects consumed 0.3 g.kg(-1).day(-1) of a placebo (trial 1) o r creatine (trial 2) for 5 days before each trial. After creatine supplemen tation, resting Delta PCr increased from 40.7 +/- 1.8 to 46.6 +/- 1.1 mmol/ kg (P = 0.04) and PCr during exercise declined from -29.6 +/- 2.4 to -34.1 +/- 2.8 mmol/kg (P = 0.02). Muscle static (Delta ATP/N) and dynamic (Delta ATP/J) costs of contraction were unaffected by creatine supplementation as well as were ATP, P-i, pH, PCr resynthesis rate, and muscle strength and en durance. Delta ATP/J and Delta ATP/N were greatest at the onset of the exer cise protocol (P < 0.01). In summary, creatine supplementation increased mu scle PCr concentration, which did not affect muscle ATP cost of contraction .