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

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

Variable	Young (baseline)^†	% increase following supplementation^‡	Old (baseline)^†	% increase following supplementation^‡
Total creatine	124.6 ± 2.7 (n = 96) [65–68]	21.7% (n = 36) [66–68]	129.8 ± 4.0 (n = 109) [20, 25, 30, 31, 42]	14.9% (n = 28) [20, 25]
Phosphocreatine	78.2 ± 2.3 (n = 96) [65–68]	13.3% (n = 36) [66–68]	78.4 ± 4.1 (n = 109) [20, 25, 30, 31, 42]	8.2% (n = 28) [20, 25]
Creatine	46.0 ± 2.3 (n = 96) [65–68]	39.3% (n = 36) [66–68]	51.4 ± 3.8 (n = 109) [20, 25, 30, 31, 42]	28.6% (n = 28) [20, 25]
ATP	24.0 ± 0.6 (n = 96) [65–68]	4.2% (n = 36) [66–68]	20.0 ± 0.6 (n = 91) [20, 25, 30, 31]	6.8% (n = 28) [20, 25]

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.
^† Younger participants were between the ages of 18-36 years old, whereas older participants were between the ages of 52-79 years old.
^‡ 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.