Inter-individual variability in adaptation of the leg muscles following a standardised endurance training programme in young women

There is considerable inter-individual variability in adaptations to endurance training. We hypothesised that those individuals with a low local leg-muscle peak aerobic capacity ((V) over dotO(2peak)) relative to their whole-body maximal aerobic capacity ((V) over dotO(2max)) would experience greater muscle training adaptations compared to those with a relatively high (V) over dotO(2peak). 53 untrained young women completed one-leg cycling to measure (V) over dotO(2peak) and two-leg cycling to measure (V) over dotO(2max). The one-leg (V) over dotO(2peak) was expressed as a ratio of the two-leg (V) over dotO(2max) (Ratio(1:2)). Magnetic resonance imaging was used to indicate quadriceps muscle volume. Measurements were taken before and after completion of 6 weeks of supervised endurance training. There was large inter-individual variability in the pre-training Ratio(1:2) and large variability in the magnitude of training adaptations. The pre-training Ratio(1:2) was not related to training-induced changes in (V) over dotO(2max) (P = 0.441) but was inversely correlated with changes in one-leg (V) over dotO(2peak) and muscle volume (P < 0.05). No relationship was found between the training-induced changes in two-leg (V) over dotO(2max) and one-leg (V) over dotO(2peak) (r = 0.21; P = 0.129). It is concluded that the local leg-muscle aerobic capacity and Ratio(1:2) vary from person to person and this influences the extent of muscle adaptations following standardised endurance training. These results help to explain why muscle adaptations vary between people and suggest that setting the training stimulus at a fixed percentage of (V) over dotO(2max) might not be a good way to standardise the training stimulus to the leg muscles of different people.