Live high:train low increases muscle buffer capacity and submaximal cycling efficiency

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Abstract
This study investigated whether hypoxic exposure increased muscle buffer capacity (βm) and mechanical efficiency during exercise in male athletes. A control (CON, n=7) and a live high:train low group (LHTL, n=6) trained at near sea level (600 m), with the LHTL group sleeping for 23 nights in simulated moderate altitude (3000 m). Whole body oxygen consumption (V˙O2) was measured under normoxia before, during and after 23 nights of sleeping in hypoxia, during cycle ergometry comprising 4×4‐min submaximal stages, 2‐min at 5.6 ± 0.4 W kg–1, and 2‐min ‘all‐out’ to determine total work and V˙O2peak. A vastus lateralis muscle biopsy was taken at rest and after a standardized 2‐min 5.6 ± 0.4 W kg–1 bout, before and after LHTL, and analysed for βm and metabolites. After LHTL, βm was increased (18%, P < 0.05). Although work was maintained, V˙O2peak fell after LHTL (7%, P < 0.05). Submaximal V˙O2 was reduced (4.4%, P < 0.05) and efficiency improved (0.8%, P < 0.05) after LHTL probably because of a shift in fuel utilization. This is the first study to show that hypoxic exposure, per se, increases muscle buffer capacity. Further, reduced V˙O2 during normoxic exercise after LHTL suggests that improved exercise efficiency is a fundamental adaptation to LHTL.