Post-absorptive muscle protein turnover affects resistance training hypertrophy

Area of Science:

• Exercise Physiology
• Muscle Biology
• Molecular Biology

Background:

• Resistance exercise training (RET) influences skeletal muscle protein turnover.
• The precise mechanisms linking basal post-absorptive protein turnover to muscle hypertrophy after RET remain unclear.

Purpose of the Study:

• To investigate the role of post-absorptive muscle protein turnover in muscle hypertrophy following 12 weeks of RET.
• To identify potential molecular mechanisms underlying changes in post-training muscle protein turnover.

Main Methods:

• 31 healthy young men underwent 3 months of supervised whole-body RET.
• Muscle biopsies and blood samples were analyzed for protein turnover using stable isotope tracers (¹³C₆ and ¹⁵N phenylalanine).
• Assessments included lean body mass, muscle strength, vastus lateralis muscle thickness, myofiber cross-sectional area, and mRNA expression.

Main Results:

• RET significantly increased strength, lean body mass, muscle thickness, and myofiber cross-sectional area (p < 0.05).
• Muscle protein synthesis (MPS) increased by 24%, and muscle protein breakdown (MPB) decreased by 21%.
• The enhanced net muscle protein balance correlated positively with increased muscle thickness (r = 0.555, p = 0.003).

Conclusions:

• Post-absorptive muscle protein turnover is a key factor associated with muscle hypertrophy during resistance exercise training.
• Changes in basal muscle protein turnover contribute to the adaptive response to RET.