Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR

PLoS One. 2016 Feb 17;11(2):e0149082. doi: 10.1371/journal.pone.0149082. eCollection 2016.

Abstract

Reports concerning the effect of endurance exercise on the anabolic response to strength training have been contradictory. This study re-investigated this issue, focusing on training effects on indicators of protein synthesis and degradation. Two groups of male subjects performed 7 weeks of resistance exercise alone (R; n = 7) or in combination with preceding endurance exercise, including both continuous and interval cycling (ER; n = 9). Muscle biopsies were taken before and after the training period. Similar increases in leg-press 1 repetition maximum (30%; P<0.05) were observed in both groups, whereas maximal oxygen uptake was elevated (8%; P<0.05) only in the ER group. The ER training enlarged the areas of both type I and type II fibers, whereas the R protocol increased only the type II fibers. The mean fiber area increased by 28% (P<0.05) in the ER group, whereas no significant increase was observed in the R group. Moreover, expression of Akt and mTOR protein was enhanced in the ER group, whereas only the level of mTOR was elevated following R training. Training-induced alterations in the levels of both Akt and mTOR protein were correlated to changes in type I fiber area (r = 0.55-0.61, P<0.05), as well as mean fiber area (r = 0.55-0.61, P<0.05), reflecting the important role played by these proteins in connection with muscle hypertrophy. Both training regimes reduced the level of MAFbx protein (P<0.05) and tended to elevate that of MuRF-1. The present findings indicate that the larger hypertrophy observed in the ER group is due more to pronounced stimulation of anabolic rather than inhibition of catabolic processes.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biopsy
  • Exercise*
  • Humans
  • Male
  • Muscle Fibers, Skeletal / physiology*
  • Muscle Proteins / metabolism
  • Muscle Strength
  • Oxygen Consumption
  • Physical Endurance*
  • Proto-Oncogene Proteins c-akt / metabolism*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Resistance Training*
  • Signal Transduction
  • TOR Serine-Threonine Kinases / metabolism*

Substances

  • Muscle Proteins
  • RNA, Messenger
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases

Grants and funding

This study was supported by funding from the Swedish National Centre for Research in Sports to HCH (55-351/10). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.