Select Skeletal Muscle mRNAs Related to Exercise Adaptation Are Minimally Affected by Different Pre-exercise Meals that Differ in Macronutrient Profile.
Level 2 - randomized trial
Controlled experimental trial in humans
PubMed 29434550 · doi:10.3389/fphys.2018.00028
What was done
Thirteen recreationally trained young men (age 21.2 ± 1.6 years, VO2max 51.3 ± 4.8 ml/kg/min) completed a morning 90-minute cycling session at 70% VO2max with pre- and post-exercise casein ingestion (10 g and 15 g). After 2 hours of rest, participants received an isocaloric meal high in fat (FAT: 3207 kJ, 52 g protein, 51 g fat, 23 g carbohydrate) or carbohydrate (CHO: 3124 kJ, 53 g protein, 9 g fat, 109 g carbohydrate). Two hours post-meal, they completed resistance exercise (5 × 8 repetitions at 80% 1-RM of leg press and leg extension) followed by 25 g whey protein. Vastus lateralis biopsies were collected at baseline (morning) and at 1 and 3 hours post-resistance exercise to assess intramuscular mRNA expression and glycogen.
What was found
Muscle glycogen significantly decreased following resistance exercise, with no difference between meal conditions. Plasma free fatty acids were significantly higher after the FAT meal, whereas glucose and insulin were higher after CHO. At 3 hours post-resistance exercise, PDK4 mRNA was significantly higher in the FAT condition compared to CHO. Exercise altered the expression of HBEGF, INSIG1, MAFbx, MURF1, SIRT1, and myostatin, but without significant differences between dietary conditions. FOXO3A, IGF-1, PGC-1α, and VCP mRNA expression remained unchanged across the day. The abstract does not provide exact numerical values, fold-changes, or p-values for gene expression.
Why it matters
These findings suggest that acute manipulation of pre-exercise carbohydrate versus fat intake does not substantially alter the transcription of major genes governing muscle remodeling after resistance exercise, outside of substrate-utilization markers like PDK4.
Limits
The sample size was very small (n = 13) and limited entirely to young, recreationally active men. Measurements were restricted to acute transcript (mRNA) levels up to 3 hours post-exercise, which do not directly reflect muscle protein synthesis or chronic structural adaptation. Additionally, the resistance bout was preceded by a 90-minute endurance session, complicating extrapolation to resistance exercise performed alone.
Cited by
- supports The macronutrient composition of a meal consumed immediately prior to a resistance training workout is unlikely to be used as fuel during that workout.