The Effect of Caffeine on Endurance Time to Exhaustion at High Altitude
Abstract
Endurance time to exhaustion (ETX) is increased at high altitude (HA) but only after 2 weeks of continued exposure. The increase is thought to be related to a delayed depletion of muscle glycogen, secondary to HA-induced increases in the mobilization and utilization of free fatty acids (FFA). This study determined if caffeine (CAF), which stimulates FFA mobilization, could prolong ETX earlier in the HA exposure. Eight untrained men (17 to 24 yr) performed 2 ETX cycling bouts at 79% to 85% of their altitude-specific maximal oxygen consumption in each of 3 phases: at sea level (SL), after 1 h simulated exposure (acute), and after 2 weeks (chronic0 at 4300 m. Subjects received either a CAF (4 mg/kg) or a placebo drink in a double-bind cross-over design 1 h prior to each ETX bout in each phase. Subjective ratings of of perceived exertion (PE) and cardiac output (CO) were obtained during exercise. Daily caloric intake and composition were held constant. CAF did not alter ETX at SL but was increased by 54% (22.0 to 35.) min, p=.04) and 24% (30.8 to 38.5 min, p=0.11) during acute and chronic HA exposure, respectively. The improvements in ETX were determined not to be associated with substrate mobilization and utilization, or to a reduction in PE. Keywords: Endurance (physiology); Exhaustion; High altitude. (kt)
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 27, 1989
- Accession Number
- ADA212069
Entities
People
- Allen Cymerman
- Charles S. Fulco
- Laurie A. Trad
- Madeleine S. Rose
- Patricia M. Young
- Paul B. Rock
- Vincent A. Forte Jr.
Organizations
- United States Army Research Institute of Environmental Medicine