Investigating the adaptation of muscle oxygenation to resistance training for elders and young men using near-infrared spectroscopy

Purpose: The purpose of this study was to investigate the differences in resistance training adaptation on muscle oxygenation between young and elderly subjects. Groups of eleven trained young, untrained young, trained elderly, and untrained elderly (UTE) were recruited. Methods: Muscle oxygenation of the vastus lateralis muscle during 20 % maximal voluntary isometric contraction was observed using near-infrared spectroscopy. The oxygen saturation (SpO ₂) kinetics in the contraction and recovery phases was modeled with a tangential model to extract ΔSpO₂ and inflection time (IF). The median frequencies of SpO₂ data representing the change of tissue oxygenation oscillation were compared. Results: The ΔSpO₂ values for the trained groups (12.00 ± 7.86 %) were significantly higher than those for the untrained groups (5.91 ± 4.36 %, P < 0.05), and those for the young groups (11.63 ± 7.52 %) were significantly higher than those for the older groups (6.29 ± 4.70 %, P < 0.05). In the recovery phase, the IF was significantly longer for the elderly groups (10.32 ± 4.39 s, P < 0.05) than that for the young groups (6.31 ± 3.69 s). The median frequency of tissue oxygenation oscillation was significantly lower for the TE group (0.41 ± 0.12 Hz, P < 0.05) than that for the UTE group (0.57 ± 0.13 Hz). Conclusions: The increased ΔSpO ₂ in trained groups during muscle contraction may be due to lower microvascular O₂ pressure. The lower median frequency for the TE group indicates that tissue oxygenation oscillation significantly trended toward low-frequency oscillation, possibly resulting from the enhancement of vascular function.