Overreaching Attenuates Training-induced Improvements in Muscle Oxidative Capacity

The aim of this study was to determine whether muscle oxidative capacity is influenced by alterations in training volume in middle-distance runners.

Twenty-four highly trained middle-distance runners (n = 16 males; V˙O2peak = 73.3(4.3) mL·kg·min; n = 8 females, V˙O2peak = 63.2(3.4) mL·kg·min) completed 3 wk of normal training (NormTr), 3 wk of high-volume training (HVTr; a 10%, 20%, and 30% increase in training volume during each successive week from NormTr), and a 1-wk taper (TapTr; 55% exponential reduction in training volume from HVTr week 3). Before and immediately after each training period, the rate of recovery of muscle oxygen consumption (mV˙O2) of the gastrocnemius medialis was measured using near-infrared spectroscopy, with the rate constant indicating muscle oxidative capacity. Time to exhaustion (TTE) and V˙O2peak were determined during a maximal incremental treadmill test.

Twelve subjects were classified as being functionally overreached (FOR) after HVTr (decreased running TTE and high perceived fatigue), whereas the other 12 subjects were classified as acutely fatigued (AF; no decrease in running TTE). The AF group demonstrated a significant increase in muscle oxidative capacity after HVTr (rate constant: 15.1% ± 9.7% min; P = 0.009), with no further improvement after TapTr, whereas there was no change in muscle oxidative capacity for FOR at any time point (P > 0.05). Compared with the FOR group, the AF group had substantially larger improvements in TTE from pre-HVTr to post-TapTr (FOR, 8.8% ± 3.7%; AF, 3.2% ± 3.0%; P = 0.04).

The present study was able to demonstrate that muscle oxidative capacity was increased in response to a period of HVTr, but only in runners who did not develop FOR. Furthermore, runners who did not develop FOR had substantially larger performance improvements after a taper period.