Carbohydrate supplementation and endurance performance of moderate altitude residents at 4300 m

Recent work from our laboratory demonstrated that carbohydrate supplementation (CHOS) during exercise improved prolonged time-trial (TT) performance of sea-level residents (SLR) living at 4300 m while they were in daily negative energy balance (-1250 kcal·day^-1; [9]). The purposes of the current study were to determine during initial exposure to 4300 m:1) whether CHOS also improves TT performance of moderate altitude residents (MAR) who are in energy balance and 2) if acclimatization to moderate elevations benefits TT performance. Fifteen Air Force Academy (AFA) active duty members (age: 30 ± 1 yrs; mean ± SE), who had been living at ∼2000 m for 21 ± 3 months performed a maximal-effort 720-kJ cycle TT at the AFA and at Pikes Peak (PP), CO, (4300 m) on days 1 (PP1) and 3 (PP3). Daily energy intake and expenditure were maintained similarly at the AFA and PP. At the start of the TTs at PP, and then every 15 min thereafter, 9 subjects drank a 10% CHO solution (0.175 g·kg^-1 body weight) and 6 subjects drank a placebo (PLA) solution. All subjects were allowed to freely adjust the power output of the cycle ergometer and drank water ad libitum. Performance time did not differ between groups on PP1 (CHOS vs. PLA; 101 ± 8 vs. 116 ± 10 min) or PP3 (95 ± 8 vs. 107 ± 12 min). For both groups, cycle times on PP1 and PP3 were longer compared to the AFA (p < 0.01) and were improved from PP1 to PP3 (p < 0.05). Exercise intensity (i.e., % peak oxygen uptake) was maintained similarly at ∼62% during the TTs at the AFA and PP. Blood glucose was 1.5 to 2.0 mmol·L^-1 higher for CHOS vs. PLA (p < 0.01). It was concluded that CHOS provided no TT performance benefit for MAR at 4300 m when energy balance was maintained. However, the decrements in TT performance and exercise intensity were attenuated at 4300 m in MAR compared to those of SLR as a result of acclimatization attained while living for nearly 2 years at ∼2000 m.