PURPOSE: To examine the cross-sectional differences in intramuscular adenosine triphosphate (ATP), free creatine (FCr), phosphocreatine (PCr) and total creatine (TCr) relative to aging in males. METHODS: Recreationally-active male participants between the ages of 20 and 75 were recruited for this study. Groups were segregated by age cohorts categorized by 5-yr intervals (i.e. 20–25, 30–35, 40–45, 50–55, 60–65, 70–75). Resting muscle biopsies were obtained for analysis of intramuscular ATP, FCr, PCr, TCr, and the ratio of PCr to TCr (PCr/TCr). RESULTS: A significant decrease in ATP was seen between the 20–25 yr old group and the 60–65 yr old group (22.08 ± 3.12 mmol/kg dry wt vs. 17.58 ± 2.14 mmol/kg dry wt, respectively). There was also a trend (p = 0.051) toward a significant decrease in ATP between the 20–25 yr old age group and the 70–75 yr old age group (17.58 ± 3.45 mmol/kg dry wt). There were no significant differences seen between age groups for PCr, FCr, TCr, or PCr/TCr (p > 0.05). CONCLUSIONS: The results from the present study indicate that aging has a detrimental effect on intramuscular ATP concentration. This occurred without a significant decrease in intramuscular creatine levels indicating a possible mitochondrial dysfunction resulting in the depressed ATP levels. Future investigations should delve into the possible mechanisms causing the ATP decrements caused by aging. PRACTICAL APPLICATIONS: Our findings illustrate basal ATP levels decrease as we age. Such age-related changes may affect an individual's ability to exercise at all levels, leading to diminished exercise capacity, daily physical activity and eventually lead to sarcopenia, metabolic or cardiovascular diseases. Additionally, the findings from this study could be utilized by health professionals to better prescribe or alter resistance and cardiovascular exercise to older individuals for improving length and quality of life. ACKNOWLEDEMENT: This study was supported by an NSCA doctoral student research grant.