Short inter-set rest blunts resistance exercise-induced increases in myofibrillar protein synthesis and intracellular signalling in young males

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Manipulating the rest-recovery interval between sets of resistance exercise may influence training-induced muscle remodelling. The aim of this study was to determine the acute muscle anabolic response to resistance exercise performed with short or long inter-set rest intervals. In a study with a parallel-group design, 16 males completed four sets of bilateral leg-press and knee-extension exercise at 75% of one-repetition maximum to momentary muscular failure, followed by ingestion of 25 g of whey protein. Resistance exercise sets were interspersed by 1 min (n = 8) or 5 min of passive rest (n = 8). Muscle biopsies were obtained at rest, 0, 4, 24 and 28 h postexercise during a primed continuous infusion of l-[ring-13C6]phenylalanine to determine myofibrillar protein synthesis and intracellular signalling. We found that the rate of myofibrillar protein synthesis increased above resting values from 0 to 4 h postexercise with 1 (76%; P = 0.047) and 5 min inter-set rest (152%; P < 0.001) and was significantly greater in the 5 min inter-set rest group (P = 0.001). Myofibrillar protein synthesis rates at 24–28 h postexercise remained elevated above resting values (P < 0.05) and were indistinguishable between groups. Postexercise p70S6KThr389 and rpS6Ser240/244 phosphorylation were reduced with 1 compared with 5 min inter-set rest, whereas phosphorylation of eEF2Thr56, TSC2Thr1462, AMPKThr172 and REDD1 protein were greater for 1 compared with 5 min inter-set rest. Serum testosterone was greater at 20–40 min postexercise and plasma lactate greater immediately postexercise for 1 versus 5 min inter-set rest. Resistance exercise with short (1 min) inter-set rest duration attenuated myofibrillar protein synthesis during the early postexercise recovery period compared with longer (5 min) rest duration, potentially through compromised activation of intracellular signalling.

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