Effects of periodic carbohydrate ingestion on endurance and cognitive performances during a 40-km cycling time-trial under normobaric hypoxia in well-trained triathletes.
Level 2 - randomized trial
Double-blind randomized crossover trial in humans
PubMed 30897031 · doi:10.1080/02640414.2019.1595338
What was done
Ten male triathletes (age 22.1 ± 1.1 years, VO2max 59.4 ± 1.4 ml/kg/min) completed three 40-km cycling time-trial (TT) conditions in a double-blind, crossover, counter-balanced design: normoxic placebo (NPLA; FiO2 = 20.9%), hypoxic placebo (HPLA; FiO2 = 16.3%), and hypoxic carbohydrate (HCHO; 6% CHO provided at 2 ml/kg every 15 min; FiO2 = 16.3%). Researchers evaluated TT performance, physiological markers (SpO2, HR, RPE, blood glucose, lactate), cognitive task performance (reaction speed and accuracy), and prefrontal cerebral haemodynamics.
What was found
Hypoxia reduced 40-km cycling TT performance by ~3.5-4% (p < 0.05), and carbohydrate ingestion did not alter TT performance under hypoxia. For the cognitive task, carbohydrate ingestion slightly preserved exercise-induced cognitive reaction speed under hypoxia but did not alter response accuracy. Carbohydrate supplementation did not preserve the hypoxia-induced decrease in prefrontal cerebral blood flow (Hb-Diff) or the increase in deoxyhaemoglobin (HHb; p < 0.05), failing to prevent reductions in prefrontal tissue oxygen saturation.
Why it matters
This study indicates that while carbohydrate intake does not counteract hypoxia-induced endurance decrements or cerebral deoxygenation, it may offer selective protection for cognitive reaction speed during endurance efforts under hypoxic conditions.
Limits
The sample size was very small (n = 10) and limited to young, well-trained male triathletes. The abstract does not provide exact times, reaction latencies, or effect sizes for the cognitive outcomes. Testing was conducted under simulated normobaric hypoxia rather than actual high-altitude hypobaric hypoxia.
Cited by
- supports Under hypoxic conditions, providing glucose supplements does not produce the ergogenic exercise performance improvements typically observed in normoxia.