David B. Thorp

Determinants of oxygen uptake kinetics in older humans following single-limb endurance exercise training.

We hypothesised that the observed acceleration in the kinetics of exercise on‐transient oxygen uptake (V̇O2) of five older humans (77 ± 7 years (mean ± S.D.) following 9 weeks of single‐leg endurance exercise training was due to adaptations at the level of the muscle cell. Prior to, and following training, subjects performed constant‐load single‐limb knee extension exercise. Following training V̇O2 kinetics (phase 2, τ) were accelerated in the trained leg (week 0, 92 ± 44 s; week 9, 48 ± 22 s) and unchanged in the untrained leg (week 0, 104 ± 43 s; week 9, 126 ± 35 s). The kinetics of mean blood velocity in the femoral artery were faster than the kinetics of V̇O2, but were unchanged in both the trained (week 0, 19 ± 10 s; week 9, 26 ± 11 s) and untrained leg (week 0, 20 ± 18 s; week 9, 18 ± 10 s). Maximal citrate synthase activity, measured from biopsies of the vastus lateralis muscle, increased (P < 0.05) in the trained leg (week 0, 6.7 ± 2.0 μmol (g wet wt)−1 min−1; week 9, 11.4 ± 3.6 μmol (g wet wt)−1 min−1) but was unchanged in the untrained leg (week 0, 5.9 ± 0.5 μmol (g wet wt)−1 min−1; week 9, 7.9 ± 1.9 μmol (g wet wt)−1 min−1). These data suggest that the acceleration of V̇O2 kinetics was due to an improved rate of O2 utilisation by the muscle, but was not a result of increased O2 delivery.