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Table 1 Typical intramuscular high energy phosphate levels in young and old

From: The effects of age on skeletal muscle and the phosphocreatine energy system: can creatine supplementation help older adults

Variable Young (baseline) % increase following supplementation Old (baseline) % increase following supplementation
Total creatine 124.6 ± 2.7 (n = 96) [6568] 21.7% (n = 36) [6668] 129.8 ± 4.0 (n = 109) [20, 25, 30, 31, 42] 14.9% (n = 28) [20, 25]
Phosphocreatine 78.2 ± 2.3 (n = 96) [6568] 13.3% (n = 36) [6668] 78.4 ± 4.1 (n = 109) [20, 25, 30, 31, 42] 8.2% (n = 28) [20, 25]
Creatine 46.0 ± 2.3 (n = 96) [6568] 39.3% (n = 36) [6668] 51.4 ± 3.8 (n = 109) [20, 25, 30, 31, 42] 28.6% (n = 28) [20, 25]
ATP 24.0 ± 0.6 (n = 96) [6568] 4.2% (n = 36) [6668] 20.0 ± 0.6 (n = 91) [20, 25, 30, 31] 6.8% (n = 28) [20, 25]
  1. Values have been averaged from various investigations and are presented as: mean ± pooled S.E. values (n-size). References are presented as numbers next to value in brackets. Note that all studies assayed for the abovementioned metabolites (opposed to quantitation using 31P nuclear magnetic resonance spectroscopy) and these values are therefore expressed as mmol/kg muscle in dry weight.
  2. Younger participants were between the ages of 18-36 years old, whereas older participants were between the ages of 52-79 years old.
  3. All of the referenced interventions supplemented subjects either through a loading phase (i.e., 20 g/d for 5 days) or through a 14-to-24 week supplementation protocol using 5 g/d.