Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states

Abstract

Harber MP, Konopka AR, Jemiolo B, Trappe SW, Trappe TA, Reidy PT. Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states. Am J Physiol Regul Integr Comp Physiol 299: R1254 -R1262, 2010. First published August 18, 2010 doi:10.1152/ajpregu.00348.2010.-The purpose of this investigation was to assess mixed-muscle fractional synthesis rate (FSR) and the expression of genes involved in skeletal muscle remodeling after aerobic exercise in the fasted and fed states. Eight recreationally active males (25 Ϯ 1 yr; V O2 max: 52 Ϯ 2 ml·kg Ϫ1 ·min Ϫ1 ) performed 60-min of cycle ergometry at 72 Ϯ 1% V O2 max on two occasions in a counter-balanced design. Subjects ingested a noncaloric placebo (EX-FAST) or a beverage containing (per kg body wt): 5 kcal, 0.83 g carbohydrate, 0.37 g protein, and 0.03 g fat (EX-FED) immediately and 1 h after exercise. FSR was assessed at rest and following exercise with the use of a L-[ring 2 H5]-phenylalanine infusion combined with muscle biopsies at 2 and 6 h postexercise. mRNA expression was assessed at 2 and 6 h postexercise via real-time RT-PCR. FSR was higher (P Ͻ 0.05) after exercise in both EX-FAST (0.112 Ϯ 0.010%·h Ϫ1 ) and EX-FED (0.129 Ϯ 0.014%·h Ϫ1 ) compared with rest (0.071 Ϯ 0.005%·h Ϫ1 ). Feeding attenuated the mRNA expression (P Ͻ 0.05) of proteolytic factors MuRF-1 (6 h) and calpain-2 (2 and 6 h) postexercise but did not alter FOXO3A, calpain-1, caspase3, or myostatin mRNA expression compared with EX-FAST. Myogenic regulatory factor (MRF4) mRNA was also attenuated (P Ͻ 0.05) at 2 and 6 h postexercise in EX-FED compared with EX-FAST. These data demonstrate that a nonexhaustive bout of aerobic exercise stimulates skeletal muscle FSR in the fasted state and that feeding does not measurably enhance FSR between 2 and 6 h after aerobic exercise. Additionally, postexercise nutrient intake attenuates the expression of factors involved in the ubiquitin-proteosome and Ca 2ϩ -dependent protein degradation pathways. These data provide insight into the role of feeding on muscle protein metabolism during recovery from aerobic exercise. protein turnover; endurance; proteolysis; muscle-specific RING finger protein-1; calpain AEROBIC EXERCISE ACUTELY (8, 44) and chronically (41, 45) alters skeletal muscle protein metabolism. The influence of nutrient supply (i.e., feeding) on skeletal muscle protein kinetics following exercise that is considered to be aerobic or endurancenatured remains relatively unexplored. Levenhagen et al. (29) initially showed that ingestion of minimal amounts of carbohydrate (8 g) combined with 10 g of protein creates a positive protein balance across the leg following aerobic exercise, apparently through promoting muscle protein synthesis with little influence on protein breakdown. Recently, it was reported that coingestion of protein and carbohydrate following aerobic exercise stimulates muscle protein synthesis greater than carbohydrate intake alone and yields a net positive whole-body protein balance (24). Whi...

Physiological stimuli necessary for muscle hypertrophy

“…Importantly, cell swelling has been shown to trigger protein synthesis through the activation of mTOR and mitogen-activated protein kinase (MAPK) 40) . Previous studies confirmed that a bout of continuous cycling (30-60 min at 40-75% V ・ O2max) was effective in temporarily increasing thigh thickness (swelling) (unpublished data), activating both the mTOR 43) and MAPK 44) signaling pathways, and increasing muscle protein synthesis 45) . Hence the contribution of intracellular fluid pressure and cellular swelling may explain muscle hypertrophy that results from cycle exercise.…”

“…A study by Harber et al (2010) showed that Forkhead transcription factor 3A (FOXO3A), which is an indicator of proteolytic systems, significantly decreased 6 h after an acute bout of 60 min cycle exercise compared to rest 45) . Furthermore, 12 weeks of cycle training, which induced muscle hypertrophy, significantly lowered the resting level of mRNA expression of FOXO3A 47,48) .…”

Cycle training induces muscle hypertrophy and strength gain: strategies and mechanisms

“…Konopka et al (27,44) have shown that 12-week cycle training induced muscle hypertrophy and significantly reduced mRNA expression of Forkhead transcription factor 3A (FOXO3A) at rest with a trend for its downstream targets, Atrogin-1 and MuRF1, to also be reduced. Furthermore, FOXO3A significantly decreased 6 hours after an acute bout of 60-minute cycle exercise compared to rest (28). Therefore, following a bout of cycle exercise, the reduction of proteolytic mRNA expression may be another factor contributing to muscle hypertrophy.…”

“…Several mitogen-activated protein kinase (MAPK) signaling pathways such as extracellular signal-regulated kinase (ERK) and p38-MAPK signaling pathways also play an important role in muscle protein synthesis (16,53). Some studies have shown that a bout of cycle exercise activated both mTOR (55) and MAPK (87) signaling pathway as well as muscle protein synthesis (28). However, the magnitude of increase appears to be smaller for cycle exercise compared to resistance exercise.…”

“…Therefore, cycle training that consists of repetitive movements may suffice as a minimum stimulus required to increase muscle protein synthesis. In fact, previous studies have shown that protein synthesis acutely (28) and chronically (77) can be stimulated by cycling in untrained subjects. Furthermore, muscle hypertrophy by cycle training is frequently observed when cycle training has been performed for relatively long periods (24,58,62).…”