In vivo evidence of an age-related increase in ATP cost of contraction in the plantar flexor muscles

Impaired skeletal muscle efficiency potentially contributes to the age-related decline in exercise capacity and may explain the altered hemodynamic response to exercise in the elderly. Thus, we examined whether 1) the ATP cost of contraction increases with age, and 2) this results in altered convective O2 delivery to maintain microvascular oxygenation in the calf muscle. To this aim, we used an integrative experimental approach combining phosphorus magnetic resonance spectroscopy (31P-MRS), Doppler ultrasound imaging, and near-infrared spectroscopy (NIRS) during dynamic plantar flexion exercise at 40% of maximal power output (WRmax) in 20 healthy young and 20 older subjects matched for physical activity. The ATP cost of contraction was significantly higher in the old (7.2 ± 4.1 mM.min-1.W-1) compared with the young (2.4 ± 1.9 mM.min-1.W-1, P<0.05) and this was only significantly correlated with plantar flexion WRmax in the old (r=-0.52, P<0.05). Even when differences in power output were taken into account, end-exercise blood flow (old: 259 ± 168; young: 134 ± 40 ml.min-1.W-1, P<0.05) and convective O2 delivery (old: 0.048 ± 0.031; young: 0.026 ± 0.008 L.min-1.W-1, P<0.05) were greater in the old in comparison to the young. In contrast, NIRS oxy-, deoxy-hemoglobin and microvascular oxygenation indices were not significantly different between groups (P</i>>0.05). Therefore, this study reveals that, while the periph...
Source: Clinical Science - Category: Biomedical Science Authors: Source Type: research