We aimed to determine if the time that muscle is under loaded tension during low intensity resistance exercise affects the synthesis of specific muscle protein fractions or phosphorylation of anabolic signalling proteins. Eight men (24±1 y, BMI= 26.5±1.0 kg•m-2) performed 3 sets of unilateral knee extension exercise at 30% of 1-repetition maximum strength involving concentric and eccentric actions that were 6 sec in duration to failure (SLOW) or a work-matched bout that consisted of concentric and eccentric actions that were 1 sec in duration (CTL). Participants ingested 20 g of whey protein immediately after exercise and again at 24 h recovery. Needle biopsies (vastus lateralis) were obtained while fasted at rest and after 6, 24, and 30 h post-exercise in the fed-state following a primed, constant infusion of L-[ring-13C6]phenylalanine. Myofibrillar protein synthetic rate was higher in SLOW condition versus CTL after 24-30 h recovery (P<0.001) and correlated to p70S6K phosphorylation (r=0.42, p=0.02). Exercise-induced rates of mitochondrial and sarcoplasmic protein synthesis were elevated by 114% and 77%, respectively, above rest at 0-6 h post-exercise only in the SLOW condition (both P<0.05). Mitochondrial protein synthesis rates were elevated above rest during 24-30 h recovery in the SLOW (175%) and CTL (126%) conditions (both P<0.05). Lastly, muscle PGC-1α expression was increased at 6 h post-exercise compared to rest with no difference between conditions (main effect for time, P<0.001). These data show that greater muscle time under tension increased the acute amplitude of mitochondrial and sarcoplasmic protein synthesis and also resulted in a robust, but delayed stimulation of myofibrillar protein synthesis 24-30 h after resistance exercise.
