01-07-2007 | Original Article
Insights into central and peripheral factors affecting the “oxidative performance” of skeletal muscle in aging
Published in: European Journal of Applied Physiology | Issue 5/2007
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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.