Muscle time under tension during resistance exercise stimulates differential muscle protein sub-fractional synthetic responses in men

Abstract

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 years (sem), BMI = 26.5 ± 1.0 kg m(-2)) performed three sets of unilateral knee extension exercise at 30% of one-repetition maximum strength involving concentric and eccentric actions that were 6 s in duration to failure (SLOW) or a work-matched bout that consisted of concentric and eccentric actions that were 1 s 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-(13)C(6)]phenylalanine. Myofibrillar protein synthetic rate was higher in the 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.

Figures

Figure 1. Schematic diagram of the experimental infusion protocols

Double arrows indicate bilateral biopsies were obtained at corresponding time points. Subjects consumed 20 g of whey protein isolate at the feeding time points.

Figure 2. Percentage increase in vastus lateralis activation during the concentric phase of resistance exercise (A) and the change in mean power frequency (MPF) during the isometric phase of resistance exercise from the first repetition to the last repetition (B)

Numbers in parentheses following SLOW indicate set number. Lower case letter indicates significantly different from CTL for sets 1–3: a, SLOW(1); b, SLOW(2); c, SLOW(3); P < 0.05. *Significantly different from 0% set completion, P < 0.05. †Significantly different from CTL at that time point, P < 0.05.

Figure 3. Myofibrillar (A), mitochondrial (B), and sarcoplasmic (C) protein fractional synthetic rates (FSR) during protocols

Note different scales on y-axes between graphs. Rates are from rested fasted and after resistance exercise with slow (SLOW) or external work match control (CTL) muscle time under tension. Values are means ± S.E.M. *Significantly different from fasting, P < 0.05. †Significantly different from CTL at that same time point, P < 0.05. ‡Significantly different from the 0–6 h response in the same condition, P < 0.05.

Figure 4. Ratio of phosphorylated to total of p70S6KThr389 (A), 4E-BP1Thr37/46 (B) and p90RSKThr573 (C) during the protocols

Ratios are from rested fasted and after resistance exercise with slow (SLOW) or external work match control (CTL) muscle time under tension. Values are means ± S.E.M. Data are expressed in arbitrary units (AU). *Significantly different from fast, P < 0.05. †Significantly different from CTL within that time point, P < 0.05. ‡Significantly different from SLOW within that time point, P < 0.05.

Figure 5. Peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) mRNA content at fast, 6 h and 24 h post-exercise

*Significantly different from fasting, P < 0.05.