Abstract
This study investigated how high-altitude (HA, 4300 m) acclimatization affected exogenous glucose oxidation during aerobic exercise. Sea-level (SL) residents (n = 14 men) performed 80-min, metabolically matched exercise (O2 ∼ 1.7 L/min) at SL and at HA < 5 h after arrival (acute HA, AHA) and following 22-d of HA acclimatization (chronic HA, CHA). During HA acclimatization, participants sustained a controlled negative energy balance (-40%) to simulate the “real world” conditions that lowlanders typically experience during HA sojourns. During exercise, participants consumed carbohydrate (CHO, n = 8, 65.25 g fructose + 79.75 g glucose, 1.8 g carbohydrate/min) or placebo (PLA, n = 6). Total carbohydrate oxidation was determined by indirect calorimetry and exogenous glucose oxidation by tracer technique with 13C. Participants lost (P ≤ 0.05, mean ± SD) 7.9 ± 1.9 kg body mass during the HA acclimatization and energy deficit period. In CHO, total exogenous glucose oxidized during the final 40 min of exercise was lower (P < 0.01) at AHA (7.4 ± 3.7 g) than SL (15.3 ± 2.2 g) and CHA (12.4 ± 2.3 g), but there were no differences between SL and CHA. Blood glucose and insulin increased (P ≤ 0.05) during the first 20 min of exercise in CHO, but not PLA. In CHO, glucose declined to pre-exercise concentrations as exercise continued at SL, but remained elevated (P ≤ 0.05) throughout exercise at AHA and CHA. Insulin increased during exercise in CHO, but the increase was greater (P ≤ 0.05) at AHA than at SL and CHA, which did not differ. Thus, while acute hypoxia suppressed exogenous glucose oxidation during steady-state aerobic exercise, that hypoxic suppression is alleviated following altitude acclimatization and concomitant negative energy balance.
Highlights
Ingesting carbohydrate during endurance exercise at sea level (SL) increases exogenous carbohydrate oxidation and limits endogenous carbohydrate utilization (Jeukendrup et al, 1997; Jeukendrup, 2004, 2008)
Dietary intakes during the sea level and high-altitude phases did not differ between groups (Table 2), with the exception of relative carbohydrate intake (CHO: 3.1 ± 0.3; PLA: 2.7 ± 0.2 g/kg/d, P < 0.05) and contribution of total energy derived from carbohydrate (CHO: 48 ± 1; PLA: 45 ± 1%, P < 0.05), which was attributable to ingestion of the carbohydrate beverage (145 g carbohydrate) during the chronic HA exposure (CHA) substrate oxidation experiment on day 22 at HA, and two additional practice trials on days 7 and 14 at HA
This study investigated the effects of hypoxia, before and after development of altitude acclimatization, on oxidation of exogenous glucose ingested during steady-state exercise in healthy, young SL residents sojourning at HA while in negative energy balance
Summary
Ingesting carbohydrate during endurance exercise at sea level (SL) increases exogenous carbohydrate oxidation and limits endogenous carbohydrate utilization (Jeukendrup et al, 1997; Jeukendrup, 2004, 2008). In one of the aforementioned studies, Peronnet et al (2006) compared exogenous carbohydrate oxidation during exercise performed at the same absolute intensity and metabolic rate (i.e., V O2 = ∼2.2 L/min, 11.6 kcal/min) in normoxia (54% V O2max) and hypoxia equivalent to 4,300 m (78% V O2max), and reported that exogenous carbohydrate oxidation was again the same in hypoxia as normoxia, despite increases in both total and endogenous carbohydrate oxidation in hypoxia. Whether oxidation rate of exogenous carbohydrate ingested would differ during exercise performed at the same absolute intensity in normoxic and hypoxic conditions at exercise intensities eliciting less than maximal exogenous carbohydrate oxidation rates at HA has not been determined. Previous investigations of the effect of hypoxia on exogenous carbohydrate oxidation during exercise have studied unacclimatized lowlanders (Peronnet et al, 2006; O’Hara et al, 2017), and how altitude acclimatization affects exogenous carbohydrate oxidation during exercise is not known. We hypothesized that exogenous carbohydrate oxidation in lowlanders consuming carbohydrate during exercise in hypoxic conditions would be the same or lower during acute hypoxic exposure compared to exercise at SL, and that exogenous carbohydrate oxidation would increase with HA acclimatization
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