Self-selected Exercise Intensity Decreases But Perception Of Effort Remains Constant During A Cycle Time-trial At Altitude

Abstract

Self-selected exercise intensity during a time-trial is regulated within the brain by peripheral sensory feedback (e.g., perception of effort) and the anticipated workload remaining (Abbiss, 2008). PURPOSE: To determine whether a decrease in arterial oxygen saturation (SaO2) during an acute exposure to altitude affects self-selected exercise intensity and perception of effort during a cycle time trial. METHODS: Twenty-six male lowlanders of similar age (22±1 yr; mean±SE), weight (81±4 kg), and sea-level (SL) peak oxygen uptake (47.6±1.9 ml/kg/min) first completed a maximal effort 720 kJ cycle time-trial at SL and then again within 4 h of exposure to either 3000 m (n=6), 3500 m (n=8) or 4300 m (n=12) altitude in a hypobaric chamber. SaO2, heart rate (HR), and rating of perceived exertion (RPE) were measured every 5-min during the cycle time-trial and the respective overall means were calculated. The overall mean work rate and altitude-specific percent of maximum work rate (%WRmax) maintained during the time-trial were calculated for each altitude. RESULTS: Time-trial performance (min) was impaired (p<0.05) by ∼32% from SL values (73±5) to 3000 m (97±10), by ∼38% from SL to 3500 m (104±9) and by ∼65% from SL to 4300 m (120±7). SaO2 (%) was decreased (p<0.05) from SL values (97±1) at 3000 m (87±1), 3500 m (83±1) and 4300 m (74±1). HR (beats/min) did not change from SL values (165±3) at 3000 m (150±5) or 3500 m (150±4), but was decreased (p<0.05) at 4300 m (148±3). %WRmax did not change from SL values (60±2%) at 3000 m (53±3%), but was decreased (p<0.05) at 3500 m (50±3%) and 4300 m (46±3%). RPE did not change from SL values (14±1) at any altitude. The decrease in %WRmax was correlated (r=0.40; p<0.05) to the decrease in SaO2 with increasing altitude. CONCLUSION: These results demonstrate that during an acute exposure to altitude, self-selected exercise intensity (e.g., %WRmax) is decreased proportional to the decrease in SaO2 during a cycle time trial but perceived exertion is maintained around 14 (i.e., somewhat hard to hard) regardless of altitude. Funding provided by US Army MRMC ATO IV.MD2006.01. Authors' views not official US Army or DoD policy.