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1 Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
2 University College of Physical Education and Sports, Astrand Laboratory, Sweden; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
3 Astrand Laboratory, University College of Physical Education and Sports, Stockholm, Sweden
* To whom correspondence should be addressed. E-mail: eva.blomstrand{at}gih.se.
The aim of the study was to compare the training stimuli of eccentric (lengthening) and concentric (shortening) contractions regarding the effect on signaling enzymes involved in protein synthesis. Ten male subjects performed 4 x 6 maximal eccentric contractions on one leg followed by 4 x 6 maximal concentric contractions on the other. Six additional subjects performed the same protocol, but with maximal concentric and submaximal eccentric exercise of equal force to that of the maximal concentric contractions. Muscle biopsy samples were taken from the vastus lateralis before, immediately after, 1 h and 2 h after exercise in both legs. The average peak force produced during the maximal eccentric exercise was 31% higher than during the maximal concentric exercise, 2490 (±100) N vs. 1894 (±108) N (P<0.05). The maximal eccentric contractions led to 2-8 fold increases in the phosphorylation of p70S6 kinase (p70S6k) and the ribosomal protein S6 that persisted for 2 h into recovery, but no significant changes in phosphorylation of Akt or mTOR. Maximal concentric and submaximal eccentric contractions did not induce any significant changes in Akt, mTOR, p70S6k or S6 phosphorylation up to 2 h after exercise. The results indicate that one session of maximal eccentric contractions activates p70S6k in human muscle via an Akt independent pathway, and suggest that maximal eccentric contractions are more effective than maximal concentric contractions in stimulating protein synthesis in the absence of a nutritional intake. An effect that may be mediated through a combination of greater tension and stretching of the muscle.
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