Postexercise skeletal muscle signaling responses to moderate- to high-intensity steady-state exercise in the fed or fasted state.
Level 3 - non-randomized controlled study
Controlled crossover laboratory study without stated randomization in the abstract
PubMed 30512989 · doi:10.1152/ajpendo.00311.2018
What was done
Eight male participants (mean age 25 ± 2 yr, VO2peak 47.9 ± 3.8 ml·kg⁻¹·min⁻¹) performed 1 h of cycling at 70% Wmax in the fasted state (FAST) or 2 h after ingesting a carbohydrate-rich mixed-macronutrient breakfast (FED). Venous blood samples and vastus lateralis muscle biopsies were collected pre-, immediately post-, and 3 h post-exercise to analyze circulating metabolites, energy signaling pathways (AMPK Thr172, CREB Ser133), and metabolic gene expression (PDK4, PPARGC1A).
What was found
Plasma nonesterified fatty acid and glycerol concentrations were elevated during FAST versus FED, but exercise substrate utilization did not differ. Postexercise AMPK Thr172 phosphorylation increased ~2.5-fold overall and was ~30% higher in FAST than FED. CREB Ser133 phosphorylation was elevated ~2-fold during FAST, although it acutely decreased by ~50% immediately post-exercise. PDK4 mRNA increased 3- to 4-fold with exercise and was ~2-fold higher throughout FAST. PPARGC1A mRNA was similarly upregulated (~10-fold) in both conditions.
Why it matters
This study shows that moderate- to high-intensity exercise in the fasted state enhances specific muscle signaling (AMPK) and lipid gene expression (PDK4) compared to the fed state, without altering whole-body fat oxidation or PGC-1α upregulation acutely.
Limits
The study is limited by a very small sample size (n = 8) of young males only. The abstract does not report randomization of trial order, and only acute (up to 3 h) biochemical markers were measured rather than sustained training adaptations.
Cited by
- contradicts Exercising in a fasted state increases mitochondrial adaptations compared to exercising fed.