Creatine supplementation and age influence muscle metabolism during exercise.
Level 3 - non-randomized controlled study
Non-randomized sequential within-subject trial with age-group comparisons
PubMed 9760327 · doi:10.1152/jappl.1998.85.4.1349
What was done
Nine healthy men and women—5 young (30 ± 5 years) and 4 middle-aged (58 ± 4 years)—completed single-leg knee-extension exercise inside a whole-body magnetic resonance system across two trials 7 days apart. Each trial consisted of two 2-minute exercise bouts and a third bout continued to exhaustion, separated by 3 minutes of recovery. Participants consumed 0.3 g·kg⁻¹·day⁻¹ of placebo for 5 days before trial 1, and 0.3 g·kg⁻¹·day⁻¹ of creatine for 5 days before trial 2. Phosphorus-31 magnetic resonance spectroscopy (31P-MRS) was used to measure intramuscular pH and relative concentrations of inorganic phosphate, phosphocreatine (PCr), and beta-ATP every 10 seconds.
What was found
During the baseline placebo trial, middle-aged participants had lower resting PCr (35.0 ± 5.2 vs. 39.5 ± 5.1 mmol/kg, P < 0.05) and lower mean initial PCr resynthesis rates (18.1 ± 3.5 vs. 23.2 ± 6.0 mmol·kg⁻¹·min⁻¹, P < 0.05) compared with young participants. After creatine supplementation, resting PCr increased by 15% in the young group and by 30% in the middle-aged group (both P < 0.05) to 45.7 ± 7.5 and 45.7 ± 5.5 mmol/kg, respectively. Mean initial PCr resynthesis rate in the middle-aged group increased (P < 0.05) to match the young group (24.3 ± 3.8 vs. 24.2 ± 3.2 mmol·kg⁻¹·min⁻¹). Time to exhaustion across both groups combined increased from 118 ± 34 to 154 ± 70 seconds (P < 0.05).
Why it matters
This study shows that age-related reductions in resting muscle phosphocreatine and post-exercise resynthesis kinetics can be normalized by short-term creatine loading, eliminating energetic recovery differences between middle-aged and young adults.
Limits
The sample size is extremely small (n = 9 total; 5 young, 4 middle-aged). The design was non-randomized with a fixed sequence (placebo always preceded creatine), introducing potential order or training effects. Sex-specific differences were not analyzed.
Cited by
- supports Mitochondria typically take 3 to 5 minutes to recover and resynthesize depleted intramuscular phosphocreatine stores after maximal exertion.