Adaptations to skeletal muscle with endurance exercise training in the acutely fed versus overnight-fasted state.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 20452283 · doi:10.1016/j.jsams.2010.03.002
What was done
Fourteen untrained, healthy adults (8 female, 6 male; mean age 26.6 years, VO2max 3.48 L/min) were randomized to perform four weeks of endurance cycle ergometer training (5 days per week) in either an overnight-fasted state (FAST) or an acutely carbohydrate-fed state (FED). The authors assessed respiratory exchange ratio (RER), plasma glucose, lactate, and free fatty acid concentrations during submaximal exercise, as well as vastus lateralis citrate synthase (CS) and 3-hydroxy-CoA dehydrogenase (HAD) activities, resting muscle glycogen concentration, and VO2max.
What was found
FAST training showed no effect on RER or plasma glucose, lactate, and free fatty acid concentrations during submaximal exercise. Changes in muscle CS and HAD enzyme activities did not differ significantly between FAST and FED overall (P=0.655 and P=0.549, respectively), though men responded better to FAST and women responded better to FED. The FAST group achieved significantly greater training-induced increases than FED in VO2max (P=0.014) and resting muscle glycogen concentration (P=0.047) without a gender interaction. Specific numerical magnitudes for these gains were not reported in the abstract.
Why it matters
This study shows that exercising in an overnight-fasted state can enhance select endurance adaptations, notably aerobic capacity and baseline glycogen storage, while suggesting potential sex-specific differences in metabolic enzyme responses.
Limits
The sample size is very small (total n=14, split across sexes and two arms), leaving subgroup analyses by gender underpowered. The intervention lasted only 4 weeks in untrained young adults, precluding extrapolation to trained athletes or long-term athletic performance. Absolute numbers and variance for the primary outcomes are omitted from the abstract.
Cited by
- supports Aerobic endurance training performed in a fasted state yields greater training adaptations compared to training in a fed state.