Maintaining Endurance Performance At High Altitude (4300 M) Despite Severe Energy Intake Deficit

Abstract

Body weight (BW) and lean body mass (LBM) of sea-level (SL) residents are typically reduced by <4% and <2%, respectively, while endurance performance is greatly impaired initially but then improves during the first three weeks of altitude exposure. PURPOSE: To determine if a greater reduction in LBM due to severe energy intake deficit will eliminate the performance improvement despite maintenance of a high carbohydrate (CHO) diet METHODS: Two groups of men (mean ± SE: 22 ± 1 yrs) were matched at SL on cycle peak oxygen uptake (VO2peak), cycle endurance performance (50% of VO2 for 50 min followed by 70% of VO2peak to exhaustion), total energy intake, and percent of energy from CHO (%CHO). At ALT, the deficit group (DEF, n = 10) consumed 1340 kcal/day (−40%) below BW maintenance requirements and the adequately fed group (ADQ, n = 7) ingested enough energy to maintain BW. Both groups ingested similar %CHO (∼64 to 71%) and >347 g of CHO/day at SL and ALT. Endurance performance was again assessed at ALT on days 1 and 18 using the identical absolute power outputs that were used at SL for 50% (149 ± 4 watts) and 70% (218 ±6 watts) VO2peak. RESULTS: From SL to day 18 at ALT, BW was reduced for DEF (80.4 ± 12 to 74.3 ± 3 kg;-8 ± 2%; P < 0.01) but not ADQ (74.4 ±3 to 73.3 ±3 kg; −1 ± 1%). Similarly, LBM (estimated from circumference measures) was reduced for DEF (71.0 ± 10 to 66.4 ± 7 kg, −6 ± 1%; P < 0.01) but not ADQ (66.3 ± 5 to 64.9 ± 5 kg; −2 ± 1%). On either day at ALT, there was no difference between groups in endurance time. For both groups, endurance performance at ALT was 6 ± 2% greater on day 18 (57 ± 2 min) than on day 1 (54 ± 1 min; P < 0.012). CONCLUSION: During the first three weeks of ALT acclimatization, a 6% loss in LBM due to underfeeding did not adversely affect the improvement in endurance performance. The lack of effect on performance during severe energy deficit may have been due to the maintenance of muscle glycogen stores or a lower rate of muscle glycogen utilization for the same amount of work.