Creatine supplementation and age influence muscle metabolism during exercise

Publisher Website
Google Scholar
Abstract
Young [ n = 5, 30 ± 5 (SD) yr] and middle-aged ( n = 4, 58 ± 4 yr) men and women performed single-leg knee-extension exercise inside a whole body magnetic resonance system. Two trials were performed 7 days apart and consisted of two 2-min bouts and a third bout continued to exhaustion, all separated by 3 min of recovery.31P spectra were used to determine pH and relative concentrations of Pi, phosphocreatine (PCr), and β-ATP every 10 s. The subjects consumed 0.3 g ⋅ kg−1 ⋅ day−1of a placebo ( trial 1) or creatine ( trial 2) for 5 days before each trial. During the placebo trial, the middle-aged group had a lower resting PCr compared with the young group (35.0 ± 5.2 vs. 39.5 ± 5.1 mmol/kg, P < 0.05) and a lower mean initial PCr resynthesis rate (18.1 ± 3.5 vs. 23.2 ± 6.0 mmol ⋅ kg−1 ⋅ min−1, P < 0.05). After creatine supplementation, resting PCr increased 15% ( P < 0.05) in the young group and 30% ( P < 0.05) in the middle-aged group to 45.7 ± 7.5 vs. 45.7 ± 5.5 mmol/kg, respectively. Mean initial PCr resynthesis rate also increased in the middle-aged group ( P < 0.05) to a level not different from the young group (24.3 ± 3.8 vs. 24.2 ± 3.2 mmol ⋅ kg−1 ⋅ min−1). Time to exhaustion was increased in both groups combined after creatine supplementation (118 ± 34 vs. 154 ± 70 s, P < 0.05). In conclusion, creatine supplementation has a greater effect on PCr availability and resynthesis rate in middle-aged compared with younger persons.