Lower Oxygen Cost Of Absolute Workload Submaximal Exercise During Acute High Altitude Exposure

PURPOSE: The oxygen cost (VO2; L/min) of an aerobic activity (running, cycling) performed at a given absolute submaximal workload is generally expected to be identical whether performed at altitude or sea level (SL). However, some have reported lower submaximal VO2 during exercise at 5260 m but not 4100 m nor 2500 m compared to SL (Lundby et al., Scand J Med Sci Sports 2007:17:281-291), suggesting that the impact of elevation on VO2 during submaximal exercise varies depending on the altitude. Thus, the purpose of this investigation was to assess differences in submaximal VO2 at acute exposure to elevations between 3000 m and 4800 m compared to SL. METHODS: We retrospectively analyzed data from four different research protocols in which, within each study, volunteers exercised at the same absolute workload at SL (760 mmHg) and after ~3 hours of hypobaric hypoxia (altitude chamber). In study 1, volunteers (n = 20) walked for 20 minutes at 40% of SL VO2peak at SL and at 3000 m (522 mmHg). In study 2, volunteers (n = 13) exercised on a cycle ergometer for 25 minutes at 50% of SL VO2peak at SL and at 3500 m (497 mmHg). In study 3, volunteers walked for 20 minutes at 30% (n = 5) and 20 minutes at 50% (n = 4) of SL VO2peak at SL and at 4000 m (468 mmHg). In study 4, volunteers (n = 7) walked for 20 minutes at 35% of SL VO2peak at SL and at 4800 m (430 mmHg). RESULTS: Compared to SL, VO2 was unchanged at 3000 m (1.64 ± 0.36 vs 1.68 ± 0.39 L/min; mean ± SD; SL vs altitude; p = 0.15) and 3500 m (1.76 ± 0.31 vs 1.63 ± 0.24 L/min; p = 0.10). VO2 was also unchanged compared to SL at 4000 m during 30% VO2peak (1.23 ± 0.14 vs 1.13 ± 0.15 L/min; p = 0.15) but was significantly lower compared to SL at 4000 m during 50% VO2peak (2.08 ± 0.13 vs 1.83 ± 0.16 L/min; p = 0.02). Lastly, compared to SL, VO2 was significantly lower at 4800 m compared to SL (1.21 ± 0.17 vs 1.09 ± 0.16 L/min; p = 0.01). CONCLUSION: Our findings indicate that the impact of acute elevation on VO2 during submaximal exercise can be influenced by altitude severity and exercise intensity. While the mechanisms for these differences are unclear, this may be related to lower oxygen availability at the higher altitudes. DISCLAIMER: The views expressed in this abstract are those of the authors and do not necessarily reflect the positions or policies of the US Army Research Institute of Environmental Medicine, the US Army, or US Department of Defense.