Anabolic Signaling Phosphorylation Does Not Explain Differential Muscle Protein Synthesis with Intra-Set Rest Manipulation

Abstract

Power development is imperative for dynamic sport athletes. Cluster sets (CLU) are an effective method to allay the progressive decrement in power output normally observed in a traditional (TRD) resistance exercise strategy. CLU configurations incorporate a brief intra-set rest period to preserve velocity and power. Despite favorable performance, we previously established that TRD configurations elicit higher myofibrillar protein synthesis (MPS) rates when compared to CLU. However, it remains unclear if hallmark readouts related to mTORC1-signaling underlie this observation. PURPOSE: To elucidate anabolic signaling mechanisms driving differential MPS rates observed between CLU and TRD paradigms of the barbell back squat in trained men and women. METHODS: In randomized crossover design, 8 resistance-trained adults (7M, 1F; 23 ± 4 y; LBM, 63 ± 9 kg; back squat 1RM, 150 ± 26 kg) performed an acute bout of either CLU (4 sets × (2 × 5) repetitions, 30s intra-set rest, 90s inter-set rest) or TRD (4 sets × 10 repetitions, 120s inter-set rest) barbell back squats at ~70% 1RM. Volume load and total rest were matched between bouts. Participants ingested 20g of whey protein immediately before and after exercise. Muscle biopsies were collected at rest and at 0, 2, and 5 h post-exercise during primed-continuous L-[ring-13C6]phenylalanine infusions. Total and phosphorylated states of targeted proteins were assessed through immunoblotting. Data was normalized to an internal loading control. RESULTS: The phosphorylation of focal adhesion kinase (FAK) was doubled with TRD, but not significantly different, from CLU (TRD 2.1 ± 0.9-fold increase from baseline; CLU 1.3 ± 0.9-fold; p>0.05). Downstream targets of mTORC1 also showed no differences in phosphorylation between paradigms (4E-BP1: TRD 1.6 ± 0.3-fold, CLU 0.4 ± 0.2-fold; p706SK: TRD 1.5 ± 0.4-fold, CLU 0.9 ± 0.4-fold). Similarly, there was no difference in AMPK phosphorylation between conditions (TRD 1.3 ± 0.9-fold; CLU 0.9 ± 0.7-fold). CONCLUSION: Our data demonstrated that changes in protein phosphorylation as noted by various readouts within the mTORC1 pathway do not underpin the greater post-exercise muscle protein synthetic response with TRD versus CLU-style in resistance trained men and women.