1. Biopsy specimens of muscle obtained after an overnight rest from 14 men and eight women, apparently healthy subjects (age range 52–79 years), were analysed for pyruvate, lactate and energy-rich phosphagens.
2. Values for metabolites showed no sex differences. Compared with previous findings in men and women about 40 years younger, the intramuscular concentrations of both total adenine nucleotides and phosphocreatine were approximately 5% lower in the elderly. Creatine was correspondingly increased, but total creatine was unchanged, as were the ATP and the ATP/ADP ratio.
3. It was concluded that energy-rich compounds showed significant but small age-related variations.