Overreaching Attenuates Training-induced Improvements in Muscle Oxidative Capacity

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Abstract
Introduction: The aim of this study was to determine whether muscle oxidative capacity is influenced by alterations in training volume in middle-distance runners. Methods: Twenty-four highly trained middle-distance runners (n = 16 males; V˙O2peak = 73.3(4.3) mL·kg−1·min−1; n = 8 females, V˙O2peak = 63.2(3.4) mL·kg−1·min−1) 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. Results: 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−1; 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). Conclusion: 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.

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