Submitted on January 5, 2005
Accepted on April 22, 2005
Carbohydrate Supplementation Improves Time-Trial Cycle Performance During Energy Deficit at 4300 m Altitude
C. S. Fulco1*, K. W. Kambis2, A. L. Friedlander3, P. B. Rock4, S. R. Muza1, and A. Cymerman1
1 Thermal and Mountain Medicine Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA, USA
2 Department of Kinesiology, The College of William and Mary, Williamsburg, VA, USA
3 VA Palo Alto Health Care System, Palo Alto, CA, USA
4 Center for Aerospace and Hyperbaric Medicine, Oklahoma State University, Tulsa, OK, USA
* To whom correspondence should be addressed. E-mail: charles.fulco{at}US.army.mil.
Carbohydrate supplementation (CHOS) during prolonged cycling at sea level (SL) enhances glucose availability and oxidation, and allows sustained higher intensity exercise compared to no CHOS. This study determined if CHOS also improves performance while residing at high altitude (ALT, 4300 M) despite hypoxemia exacerbated by high intensity exercise. To simulate negative energy balance that typically occurs while living at ALT for 10 days, energy expenditure was increased (~500 kcal.d-1 ) and energy intake was reduced (~750 kcal.d-1 ) compared to SL. After an overnight fast, 2 groups of fitness-matched men performed a maximum effort, 720 KJ cycle time trial (TT) at SL and while living at ALT on days 3 (ALT3) and 10 (ALT10). 8 men drank a 10% CHO solution (0.175 g.kg-1 bw; e.g., 14 g CHO, 56 kcals and 140 mls[[rad]]serving-1 for 80 kg bw) and 8 drank a placebo (PLA; double-blind) at the start of and every 15 min of the TT. All freely adjusted watts and drank water. Blood glucose and O2 saturation (SaO2) were measured at rest and during exercise. For all test days, resting glucose and SaO2 were similar for both groups while glucose during exercise was higher (P<0.05) for CHOS than for PLA. At SL, TT duration (~59 min) and watts (~218 or ~61% of peak watts; %SL Wpeak) were similar for both groups. At ALT, TT duration was worse than at SL for both groups (P<0.01) but was better for CHOS than for PLA on ALT3 ((X±SE): 80±7 vs 105±9 min, P<0.01) and ALT10 (77±7 vs 90±5 min, P<0.01). At ALT, %SL Wpeak for both groups was reduced from SL (P<0.01) with the reduction on ALT3 larger for PLA (to 33±3%) than for CHOS (to 43±2%, P<0.05). On ALT3, SaO2 fell similarly from 84±2% at rest to 73±1% during the entire TT for both groups (P<0.05) and on ALT10, SaO2 fell more (P<0.02) during the TT for CHOS (91±1 to 76±2%) than for PLA (90±1 to 81±1%). There were significant inverse relationships between %SL Wpeak and SaO2 during the TT for both groups at ALT3 (r = -0.76, P<0.03) and ALT10 (r = -0.90, P<0.01). It was concluded that despite hypoxemia exacerbated by higher intensity exercise, increasing availability of glucose as a metabolic fuel greatly improved TT performance during the first 10 days of ALT residence in which there was a negative energy balance.
