Whole-body and muscle responses to aerobic exercise training and withdrawal in ageing and COPD

BACKGROUND: Chronic obstructive pulmonary disease (COPD) patients exhibit lower peak oxygen uptake (V'O2peak), altered muscle metabolism and impaired exercise tolerance compared with age-matched controls. Whether these traits reflect muscle-level deconditioning (impacted by ventilatory constraints) and/or dysfunction in mitochondrial ATP production capacity is debated. By studying aerobic exercise training (AET) at a matched relative intensity and subsequent exercise withdrawal period we aimed to elucidate the whole-body and muscle mitochondrial responsiveness of healthy young (HY), healthy older (HO) and COPD volunteers to whole-body exercise. METHODS: HY (n=10), HO (n=10) and COPD (n=20) volunteers were studied before and after 8 weeks of AET (65% V'O2peak) and after 4 weeks of exercise withdrawal. V'O2peak, muscle maximal mitochondrial ATP production rate (MAPR), mitochondrial content, mitochondrial DNA (mtDNA) copy number and abundance of 59 targeted fuel metabolism mRNAs were determined at all time-points. RESULTS: Muscle MAPR (normalised for mitochondrial content) was not different for any substrate combination in HO, HY and COPD at baseline, but mtDNA copy number relative to a nuclear-encoded housekeeping gene (mean±sd) was greater in HY (804±67) than in HO (631±69; p=0.041). AET increased V'O2peak in HO (17%; p=0.002) and HY (21%; p