This study investigated whether hypoxic exposure increased muscle buffer ca
pacity (betam)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 simul
ated moderate altitude (3000 m). Whole body oxygen consumption ((V)over dot
O(2)) was measured under normoxia before, during and after 23 nights of sle
eping in hypoxia, during cycle ergometry comprising 4 x 4-min submaximal st
ages, 2-min at 5.6 +/-0.4 W kg(-1), and 2-min 'all-out' to determine total
work and (V)over dotO(2peak). 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 a
fter LHTL, and analysed for betam and metabolites. After LHTL, gm was incre
ased (18%, P<0.05). Although work was maintained, (V)over dotO(2peak) fell
after LHTL (7%, P<0.05). Submaximal (V)over dotO(2) 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 ex
posure, per se, increases muscle buffer capacity. Further, reduced (V)over
dotO(2) during normoxic exercise after LHTL suggests that improved exercise
efficiency is a fundamental adaptation to LHTL.