PURPOSE:  Few studies have examined the effects of low to moderate altitude exposure on resting metabolic rate (RMR). Yet, changes in RMR with altitude exposure would have implications for energy requirements, and failure to adjust energy intake could lead to low energy availability (LEA). The confounding effect of LEA on RMR must also be considered given athletes may purposefully or unintentionally consume insufficient energy during training camps. As such, the aim of this study was to investigate the effects of acute and chronic altitude exposure and energy availability (EA) on RMR in female athletes. 

 

METHODS: Twenty female race walkers of Tier 4-5 calibre underwent a 3-week training camp at an altitude of ~1800 m. Athletes included a mixture of naturally menstruating athletes (n=13) and hormonal contraceptive users (n=7). During the first two weeks, all athletes consumed a diet providing an EA of 45 kcal·kg fat free mass (FFM)^-1·day^-1. During the final week, half the athletes received a LEA diet providing an EA of 15 kcal·kg FFM^-1·day^-1. The remaining athletes continued to consume a diet providing an EA of 45 kcal·kg FFM^-1·day^-1 (High EA; HEA). RMR was measured prior to travelling to altitude (baseline), and before (ALT-WK 2) and after (ALT-WK 3) the EA manipulation. Athletes in the HEA group underwent additional RMR testing at 36 hrs altitude exposure (acute), and 36 hrs post-altitude. Changes in body composition were determined before and after the training camp via Dual-energy X-ray absorptiometry. 

 

RESULTS: Athletes in both groups had unchanged FFM (p=0.909) and decreased fat mass across the training camp (p<0.0001). Although not reaching statistical significance, LEA athletes had a greater reduction in fat mass than HEA athletes (-1.00±0.60 vs -0.54±0.57 kg; p=0.05). The 7-days of LEA exposure did not impact RMR (p=0.347), and RMR was increased from baseline at ALT-WK 2 (70±74 kcal/day, p=0.001) and ALT-WK 3 (52±63 kcal/day, p=0.011). For HEA athletes, RMR was increased from baseline with acute altitude exposure (76±40 kcal/day, p=0.026) and post-altitude RMR returned to baseline (-59±101 kcal/day; p=0.124). 

CONCLUSION:  The RMR of female race walkers increased with acute exposure to an altitude of ~1800 m and remained elevated during the 3-weeks of altitude exposure, but quickly decreased upon return to sea level. A 7-day period of LEA did not impact the alteration in RMR seen with altitude exposure. Despite statistical significance, the increase in RMR at altitude (~50-75 kcal/d) is unlikely to have clinically significant implications for an athlete's total daily energy requirements. Further research is needed to assess if other components of total daily energy expenditure are altered with altitude exposure, if higher altitude magnifies findings, and how such potential adaptations contribute to changes in energy requirements.