Association of mitochondrial oxidative capacity with physical fitness in ageing: the Baltimore longitudinal study of ageing.

Participants with higher mitochondrial oxidative phosphorylation had significantly greater cardiorespiratory fitness than those with lower OxPhos.

• Participants with higher kPCr had 4.07 (95% CI: 2.88, 5.26) ml/kg/min higher MVO2 peak than those with lower kPCr.
• OxPhos was measured as phosphocreatine recovery rate (kPCr) through 31P magnetic resonance spectroscopy.
• Individuals were classified as low (≤ -0.5 SD), average (-0.5 to 0.5 SD), and high (>0.5 SD) OxPhos based on age- and sex-specific kPCr z-scores.
• The study included 649 Baltimore Longitudinal Study of Ageing participants with mean age 64.5 years, 56.9% females.

Participants with higher mitochondrial OxPhos had greater aerobic resilience than those with lower OxPhos.

• Participants with higher kPCr had 0.19 (95% CI: 0.06, 0.32) higher aerobic resilience than those with lower kPCr.
• Aerobic resilience was defined as the ratio between MVO2 peak and average VO2 during usual pace walking.
• Cardiorespiratory fitness was measured as peak oxygen consumption (MVO2 peak) during treadmill testing.

The energetic cost of walking was paradoxically greater in participants with high OxPhos compared to those with low OxPhos.

• The energetic cost of walking was greater by 0.84 (95% CI: 0.21, 1.47) ml/kg/100 m in those with high than low kPCr.
• The energetic cost of usual pace walking was expressed as the average oxygen consumption per 100 metres.
• This finding was in the opposite direction from what might be expected if higher OxPhos simply reduced energy expenditure during walking.

A multiplicative interaction between age and kPCr was identified for MVO2 peak and aerobic resilience, with OxPhos group differences attenuating after age 70.

• A multiplicative interaction between age and kPCr was identified in the regressions predicting MVO2 peak and aerobic resilience (p interaction = 0.01).
• Differences between OxPhos groups attenuated after age 70.
• This suggests the contribution of mitochondrial oxidative capacity to fitness is especially prominent in young and middle adulthood.
• The attenuation after age 70 implies that other age-related impairments may increasingly influence fitness in older adults.

The study design was cross-sectional and population-based, using a well-characterized aging cohort.

• 649 Baltimore Longitudinal Study of Ageing participants were included.
• Mean age was 64.5 years and 56.9% were female.
• Muscle mitochondrial OxPhos was measured non-invasively as phosphocreatine recovery rate (kPCr) through 31P magnetic resonance spectroscopy.
• The study investigated relationships of OxPhos with cardiorespiratory fitness, energetic cost of walking, and aerobic resilience with respect to age.