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

Abstract

Five women and 3 men (29.8 ± 1.4 yr) performed dynamic knee-extension exercise inside a magnetic resonance system (means ± SE). Two trials were performed 7–14 days apart, consisting of a 4- to 5-min exhaustive exercise bout. To determine quadriceps cost of contraction, brief static and dynamic contractions were performed pre- and postexercise.31P spectra were used to determine pH and relative concentrations of Pi, phosphocreatine (PCr), and βATP. Subjects consumed 0.3 g ⋅ kg−1 ⋅ day−1of a placebo ( trial 1) or creatine ( trial 2) for 5 days before each trial. After creatine supplementation, resting ΔPCr 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 (ΔATP/N) and dynamic (ΔATP/J) costs of contraction were unaffected by creatine supplementation as well as were ATP, Pi, pH, PCr resynthesis rate, and muscle strength and endurance. ΔATP/J and ΔATP/N were greatest at the onset of the exercise protocol ( P< 0.01). In summary, creatine supplementation increased muscle PCr concentration, which did not affect muscle ATP cost of contraction.