Alterations in purine metabolism in middle-aged elite, amateur, and recreational runners across a 1-year training cycle.

Changes in purine derivatives may be considered as signs of training-induced metabolic adaptations. The purpose of this study was to assess the effect of a 1-year training cycle on the response of hypoxanthine (Hx) concentration and Hx-guanine phosphoribosyltransferase (HGPRT) activity. Three groups of middle-aged male runners were examined: 11 elite master runners (EL; 46.0 ± 3.8 years), 9 amateur runners (AM; 45.1 ± 4.7 years), and 10 recreational runners (RE; 45.9 ± 6.1 years). Plasma Hx concentration and erythrocyte HGPRT activity were measured in three characteristic training phases of the annual cycle. Significant differences in post-exercise Hx concentration and resting HGPRT activity were demonstrated between the EL, AM, and RE groups across consecutive training phases. The EL group showed lowest Hx concentration and highest HGPRT activity compared to the AM and RE groups. Analogous differences were observed between the AM and RE groups during specific preparation. For the EL group, the changes were observed across all examinations and the lowest Hx concentration and highest HGPRT activity were found in the competition phase. Significant change was also revealed in the AM group between the general and specific preparation, but not in the competition phase. No significant changes were found in the RE runners who did not use anaerobic exercise in their training. In conclusion, a long-lasting endurance training, incorporating high-intensity exercise, results in significant changes in purine metabolism, whereas training characterized by constant low-intensity exercise does not. Plasma Hx concentration and erythrocyte HGPRT activity may be sensitive indicators of training adaptation and training status in middle-aged athletes.