Effect Of Altitude On Hiking Performance While Carrying A Weighted Backpack

Abstract

Athletic performances lasting longer than ∼1 hr can be impaired by as much as 30% to 70% at 3000 m to 4300 m from sea level (Fulco, 1998). However, the magnitude of impairment while hiking with a backpack at such altitudes has never been quantitated. PURPOSE: To determine at altitude if the relative performance impairments while hiking with a weighted backpack are similar to those observed during athletic performances. METHODS: Twenty-eight male lowlanders of similar age (22±1 yr; mean±SE), weight (82±4 kg), and SL peak oxygen uptake (47±1 ml/kg/min) completed a 8-km, 5% grade maximal effort, simulated hike on a treadmill while carrying a 16-kg backpack at sea level (SL) and again after 24-h exposure to 3000 m (n=6), 3500 m (n=8) or 4300 m (n=14) altitude in a hypobaric chamber. Heart rate (HR), arterial oxygen saturation (SaO2) and rating of perceived exertion (RPE) were measured every 5-min during the hike and the respective overall mean values were calculated. RESULTS: Seven of the volunteers exposed to 4300 m could not complete the hike and their data were excluded. Hike performance (min) was impaired (p<0.05) by ∼13% from SL (81±2) to 3000 m (92±3), by ∼19% from SL (74±3) to 3500 m (88±3) and by ∼24% from SL (81±2) to 4300 m (100±3). SaO2 (%) was decreased (p<0.05) from SL values (96±1) at 3000 m (84±1), 3500 m (80±1), and 4300 m (72±1). HR (beats/min) and RPE did not change from SL values (160±4;13±1) at either 3000 m (158±3;14±1), 3500 m (156±3;14±1), or 4300 m (153±3;13±1), respectively. CONCLUSION: These results indicate that the performance impairments at altitude that occur when hiking with a weighted backpack are smaller than those that occur during athletic events. The most likely reason for this difference is a narrowed range of movement speed due to a change in body position imposed by carrying the weighted backpack. Funding provided by US Army MRMC ATO IV.MD2006.01. Authors' views not official US Army or DoD policy.