Cycling at Altitude: Lower Absolute Power Output as the Main Cause of Lower Gross Efficiency.

PURPOSE:: To investigate the effect of altitude on GE at the same relative exercise intensity and the same absolute power output (PO). Additionally, we sought to determine the effect of altitude on the change in GE during high-intensity exercise.

METHODS:: Twenty-one trained males performed three maximal incremental tests and five GE-tests, at sea level, 1500 m and 2500 m of acute simulated altitude. The GE-tests at altitude were performed once at the same relative exercise intensity and once at the same absolute PO as at sea level.

RESULTS:: Altitude resulted in an unclear effect at 1500 m (-3.8%; ±90% CL 3.3%) and most likely negative effect at 2500 m (-6.3%; ±1.7%) on pre-GE, when determined at the same relative exercise intensity. When pre-GE was determined at the same absolute PO unclear differences in GE were found (-1.5%; ±2.6% at 1500 m, -1.7%; ±2.4% at 2500 m). The effect of altitude on the decrease in GE during high-intensity exercise was unclear when determined at the same relative exercise intensity (-0.4%; ±2.8% at 1500 m, -0.7%; ±1.9% at 2500 m). When GE was determined at the same absolute PO, altitude resulted in a substantially smaller decrease in GE (2.8%; ±2.4% at 1500 m, 5.5%; ±2.9% at 2500 m).

CONCLUSIONS:: The lower GE found at altitude, when exercise is performed at the same relative exercise intensity, is mainly caused by the lower PO at which cyclists exercise.