Resistance exercise volume affects myofibrillar protein synthesis and anabolic signalling molecule phosphorylation in young men

Abstract

We aimed to determine if any mechanistic differences exist between a single set (1SET) and multiple sets (i.e. 3 sets; 3SET) of resistance exercise by utilizing a primed constant infusion of [ring-13C6]phenylalanine to determine myofibrillar protein synthesis (MPS) and Western blot analysis to examine anabolic signalling molecule phosphorylation following an acute bout of resistance exercise. Eight resistance-trained men (24+/-5 years, BMI=25+/-4 kg m2) were randomly assigned to perform unilateral leg extension exercise at 70% concentric one repetition maximum (1RM) until volitional fatigue for 1SET or 3SET. Biopsies from the vastus lateralis were taken in the fasted state (Fast) and fed state (Fed; 20 g of whey protein isolate) at rest, 5 h Fed, 24 h Fast and 29 h Fed post-exercise. Fed-state MPS was transiently elevated above rest at 5 h for 1SET (2.3-fold) and returned to resting levels by 29 h post-exercise. However, the exercise induced increase in MPS following 3SET was superior in amplitude and duration as compared to 1SET at both 5 h (3.1-fold above rest) and 29 h post-exercise (2.3-fold above rest). Phosphorylation of 70 kDa S6 protein kinase (p70S6K) demonstrated a coordinated increase with MPS at 5 h and 29 h post-exercise such that the extent of p70S6K phosphorylation was related to the MPS response (r=0.338, P=0.033). Phosphorylation of 90 kDa ribosomal S6 protein kinase (p90RSK) and ribosomal protein S6 (rps6) was similar for 1SET and 3SET at 24 h Fast and 29 h Fed, respectively. However, 3SET induced a greater activation of eukaryotic translation initiation factor 2B (eIF2B) and rpS6 at 5 h Fed. These data suggest that 3SET of resistance exercise is more anabolic than 1SET and may lead to greater increases in myofibrillar protein accretion over time.

Figure 1. Schematic diagram of the experimental infusion protocols

Double arrows indicate bilateral biopsies were obtained at corresponding time points.

Figure 2. Increase in vastus lateralis EMG during the concentric phase of resistance exercise and change in mean power frequency during the isometric phase of resistance exercise

A, percentage increase in vastus lateralis EMG (activation) during the concentric phase of resistance exercise. Numbers in parentheses of key following 3SET indicate set number. B, the change in mean power frequency (MPF) during the isometric phase of resistance exercise. Times with different lower-case letters indicate significantly differences from first repetition (0% completion): a for 1SET, b for 3SET(1), c for 3SET(2), d for 3SET(3), P < 0.05. *Significantly different from 1SET at that time point, P < 0.05.

Figure 3. Myofibrillar protein fractional synthesis rate (FSR) at rest and 5 h after protein ingestion after one set (1SET) or 3 sets (3SET) of resistance exercise and 24–29 h later

Inset, volume load (kg times repetitions) performed during 1SET and 3SET of resistance exercise. *Significantly different from rest (P < 0.05). †Significantly different from 29 h (P < 0.05). ‡Significantly different from 1SET (P < 0.05).

Figure 4. Phosphorylation of eIF2Bɛ^Ser539 (A), p90RSK^Thr573 (B), p70S6K^Thr389 (C) and rps6^Ser240/244 (D) following one set (1SET) or 3 sets (3SET) of resistance exercise in the fasted or fed states

Data are expressed as fold-change from rest. *Significantly different from Fast (P < 0.05). †Significantly different from 1 set (1SET) within that time point (P < 0.05).

Figure 5. Relationship between myofibrillar protein synthesis and the extent of phosphorylation of p70S6K^Thr389

There was a significant (P = 0.033) correlation between the degree of phosphorylation (fold-change from basal) and myofibrillar protein synthesis (FSR, % h⁻¹).