| Summary: | <p><strong>Purpose:</strong> Aging is associated with changes in muscle energy metabolism. Proton (<sup>1</sup>H) and phosphorous (<sup>31</sup>P) magnetic resonance spectroscopy (MRS) has been successfully applied for non-invasive investigation of skeletal muscle metabolism. The aim of this study was to detect differences in adenosine triphosphate (ATP) production in the aging muscle by <sup>31</sup>P-MRS and to identify potential changes associated with buffer capacity of muscle carnosine by <sup>1</sup>H-MRS.</p>
<p><strong>Methods:</strong> Fifteen young and nineteen elderly volunteers were examined. <sup>1</sup>H and <sup>31</sup>P-MRS spectra were acquired at high field (7T). The investigation included carnosine quantification using <sup>1</sup>H-MRS and resting and dynamic <sup>31</sup>P-MRS, both including saturation transfer measurements of phosphocreatine (PCr), and inorganic phosphate (Pi)-to-ATP metabolic fluxes.</p>
<p><strong>Results:</strong> Elderly volunteers had higher time constant of PCr recovery (τ<sub><em>PCr</em></sub>) in comparison to the young volunteers. Exercise was connected with significant decrease in PCr-to-ATP flux in both groups. Moreover, PCr-to-ATP flux was significantly higher in young compared to elderly both at rest and during exercise. Similarly, an increment of Pi-to-ATP flux with exercise was found in both groups but the intergroup difference was only observed during exercise. Elderly had lower muscle carnosine concentration and lower postexercise pH. A strong increase in phosphomonoester (PME) concentration was observed with exercise in elderly, and a faster Pi:PCr kinetics was found in young volunteers compared to elderly during the recovery period.</p>
<p><strong>Conclusion:</strong> Observations of a massive increment of PME concentration together with high Pi-to-ATP flux during exercise in seniors refer to decreased ability of the muscle to meet the metabolic requirements of exercise and thus a limited ability of seniors to effectively support the exercise load.</p>
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