Contraction intensity and feeding affect collagen and myofibrillar protein synthesis rates differently in human skeletal muscle.
Level 3 - non-randomized controlled study
Non-randomized controlled experimental physiological study
PubMed 19903866 · doi:10.1152/ajpendo.00609.2009
What was done
Twenty males were evaluated in either a fasted (n = 10) or fed (n = 10) state during a unilateral leg resistance exercise protocol. Each participant performed 10 sets of knee extensions comparing light load (16% of one-repetition maximum [1RM]) in one leg versus heavy load (70% 1RM) in the contralateral leg, equalized for total lifted load. Participants received a [13C]leucine infusion, and bilateral vastus lateralis biopsies were collected at rest and at 0.5, 3, and 5.5 hours post-exercise to measure fractional synthesis rate (FSR) and signaling pathway phosphorylation via Western blot.
What was found
Intramuscular collagen FSR increased similarly following both light-load and heavy-load exercise and was not affected by feeding. In contrast, myofibrillar FSR was unaffected by light-load exercise, whereas heavy-load exercise produced a delayed increase in myofibrillar FSR (0.14 ± 0.02%/h, P < 0.05). Feeding increased resting myofibrillar FSR (P < 0.05) and maintained elevated synthesis late in the post-exercise period. Heavy-load exercise activated Rp-s6k-4E-BP1 and MAPK signaling pathways, whereas feeding primarily affected Rp-s6k and eukaryotic elongation factor 2 phosphorylation.
Why it matters
This study demonstrates distinct regulatory mechanisms for muscle subfractions: intramuscular collagen synthesis increases with exercise volume irrespective of intensity or feeding, whereas myofibrillar protein synthesis requires heavier contractile intensity and is further augmented by feeding.
Limits
The study was conducted in a small sample of 20 males, preventing generalization to females or older populations. It only measured acute signaling and synthesis rates up to 5.5 hours post-exercise, which may not directly predict long-term training adaptations.
Cited by
- contradicts The first physiological response after a training stimulus is the synthesis of collagen to reinforce fascial connective tissue containers prior to adding muscle.