Post-exercise protein synthesis rates are only marginally higher in type I compared with type II muscle fibres following resistance-type exercise

Abstract

We examined the effect of an acute bout of resistance exercise on fractional muscle protein synthesis rates in human type I and type II muscle fibres. After a standardised breakfast (31 ± 1 kJ kg−1 body weight, consisting of 52 Energy% (En%) carbohydrate, 34 En% protein and 14 En% fat), 9 untrained men completed a lower-limb resistance exercise bout (8 sets of 10 repetitions leg press and leg extension at 70% 1RM). A primed, continuous infusion of l-[ring-13C6]phenylalanine was combined with muscle biopsies collected from both legs immediately after exercise and after 6 h of post-exercise recovery. Single muscle fibres were dissected from freeze-dried biopsies and stained for ATPase activity with pre-incubation at a pH of 4.3. Type I and II fibres were separated under a light microscope and analysed for protein-bound l-[ring-13C6]phenylalanine labelling. Baseline (post-exercise) l-[ring-13C6]phenylalanine muscle tissue labelling, expressed as (∂13C/12C), averaged −32.09 ± 0.28, −32.53 ± 0.10 and −32.02 ± 0.16 in the type I and II muscle fibres and mixed muscle, respectively (P = 0.14). During post-exercise recovery, muscle protein synthesis rates were marginally (8 ± 2%) higher in the type I than type II muscle fibres, at 0.100 ± 0.005 versus 0.094 ± 0.005%/h, respectively (P < 0.05), whereby rates of mixed muscle protein were 0.091 ± 0.005%/h. Muscle protein synthesis rates following resistance-type exercise are only marginally higher in type I compared with type II muscle fibres.

Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit

“…Although sex-based differences in skeletal muscle fiber composition have been reported previously (49), these differences are unlikely to have influenced our findings, as previous studies have failed to show any meaningful fiber type-specific effects on rates of MPS (26,34).…”

Intrinsic transient tracheal occlusion training and myogenic remodeling of rodent parasternal intercostal fibers

“…Acute anabolic responses can be detected in humans and rodents within hours of the first strength-training bout [35-37]. Fast-fiber hypertrophy may occur after ITTO training [38,39], because airway occlusion appears necessary to appreciably recruit fast-fatigable rodent diaphragm fibers [30].…”

Measuring Protein Synthesis With SUnSET

“…Hence, the use of SUnSET for the measurement of skeletal muscle protein synthesis in humans is very unlikely. As a result, sensitive measurements of protein synthesis in single human muscle fibers will likely require further refinements of current isotope-based methodologies (5, 17). A final limitation of SUnSET relates to the ability to measure the free puromycin pool.…”