Forskning
February 28, 2013
Caffeine ingestion and cycling power output in low or normal muscle glycogen state
S C Lane et al, 2013, Caffeine ingestion and cycling power output in low or normal muscle glycogen state, Medicine & Science in Sports & Exercise, published online ahead of print.
ABSTRACT
Purpose: Commencing selected workouts with low muscle glycogen availability augments several markers of training adaptation compared to undertaking the same sessions with normal glycogen content. However, low glycogen availability reduces the capacity to perform high intensity (>85% of peak aerobic power {V 02peak] endurance exercise. We determined whether a low dose of caffeine could partially rescue the reduction in maximal self-selected power output observed when individuals commenced high intensity interval training (HIT) with (LOW) compared to (NORM) glycogen availability. Methods: Twelve endurance-trained cyclists/triathletes performed four experimental trials using a double-blind Latin square design. Muscle glycogen content was manipulated via exercise-diet interventions so that two experimental trials were commenced with LOW and two with NORM muscle glycogen availability. Sixty minutes prior to an experimental trial, subjects ingested a capsule containing anhydrous caffeine (CAFF; 3 mg/kg/body mass) or placebo (PLBO). Instant power output (W) was measured throughout HIT (8×5 min bouts at maximum self-selected intensity with 1 min recovery). Results: There were significant main effects for both pre-exercise glycogen content and caffeine ingestion on power output. LOW reduced power output by ~8% compared to NORM (P<0.01) whereas caffeine increased power output by 2.8% and 3.5% for NORM and LOW respectively (P<0.01.). Conclusion: We conclude that caffeine enhanced power output independently of muscle glycogen concentration but could not fully restore power output to levels commensurate with that when subjects commenced exercise with normal glycogen availability. However, the reported increase in power output does provide a likely performance benefit and may provide a means to further enhance the already augmented training response observed when selected sessions are commenced with reduced muscle glycogen availability.
