Insights into central and peripheral factors affecting the “oxidative performance” of skeletal muscle in aging

During exercises with relatively small muscle masses, limitations to exercise performance by the cardiovascular system should be significantly reduced, allowing one to fully-test the “oxidative potential” of the investigated muscles. Ten elderly males (E, 77.8 ± 2.9 years [ \( \overline{x} \pm {\text{SD}} \)]) and eight young controls (Y, 26.6 ± 3.0) underwent incremental exercises to voluntary exhaustion on a dynamic leg-extension (dominant limb) machine (knee-extension, KE) and on a cycloergometer (CYCLO). During KE the load was increased every 3 min to loads corresponding to 20, 40 and 60% of the force of one-repetition maximum (1RM). The following variables were determined (vastus lateralis muscle): concentration changes of deoxygenated haemoglobin and myoglobin (Δ[deoxy(Hb + Mb)]) by near-infrared spectroscopy (NIRS), expressed as percentage of the maximal value obtained during transient limb ischemia, and taken as an index of O₂ extraction; root mean square (RMS) and median power frequency (MDF) by electromyography. The total lifted load during KE and peak workload during CYCLO were lower in E versus Y (620.4 ± 321.9 kg vs. 1347.4 ± 458.7; 113.5 ± 23.9 W vs. 224.3 ± 41.0, respectively). During CYCLO Δ[deoxy(Hb + Mb)] peak (i.e. the value determined at exhaustion) was lower in E (44.5 ± 17.7%) versus Y (67.1 ± 22.9), whereas during KE Δ[deoxy(Hb + Mb)] peak was higher in E (56.8 ± 20.9%) versus Y (38.6 ± 15.8). “Thresholds”, that is abrupt increases in RMS slopes, were detected in Y but not in E, suggesting less recruitment or a preferential atrophy of type 2 fibers in the elderly. These findings, associated with the preserved capacity of O₂ extraction, suggest a shift towards oxidative metabolism in skeletal muscles of 78 year-old subjects, which could preserve, at least in part, their capacity to carry out exercise.