Activation of Akt as a potential mediator of adaptations that reduce muscle injury

Nicole C. Lockhart, Keith Baar, Robert S. Mazzeo, Susan V. Brooks

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Contraction-induced injury occurs when a muscle is stretched while activated (lengthening contraction). Exposure to a bout of lengthening contractions results in protection from subsequent lengthening contraction-induced injury as well as an elevation in phosphorylated Akt and p70S6K. Whether Akt or p70S6K is involved in the protection from contraction-induced injury is unclear. To test for a specific role of Akt and/or p70S6K to induce protective adaptations, we used a conditioning protocol of passive stretches that reduces contraction-induced injury with minimal involvement of other cellular responses that have been associated with the Akt signaling pathway, such as increased metabolism, cell growth, and cell death. Purpose: To determine whether activation of Akt or p70S6K is necessary to induce protective adaptations. Methods: Extensor digitorum longus muscles of anesthetized mice were administered 75 lengthening contractions in situ with or without previous exposure to 75 passive stretches 1 h, 24 h, 3 d, or 14 d prior to lengthening contractions. Results: Compared with unconditioned muscles, the deficit in isometric force and number of injured fibers 3 d following lengthening contractions were smaller by half for passive-stretch-conditioned muscles from all time points. Phosphorylation of Akt and p70S6K were analyzed by Western blot 0 or 3 h following either lengthening contractions or passive stretches. Whereas lengthening contractions increased phosphorylation of Akt at 0 h and p70S6K at 3 h, passive stretches did not at any time increase phosphorylation of Akt or p70S6K despite reducing contraction-induced injury. Conclusion: Activation of neither Akt nor p70S6K is necessary to induce adaptations that reduce the severity of contraction-induced injury.

Original languageEnglish (US)
Pages (from-to)1058-1064
Number of pages7
JournalMedicine and Science in Sports and Exercise
Issue number6
StatePublished - Jun 2006
Externally publishedYes


  • Adaptation
  • Conditioning
  • Damage
  • Passive stretching

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Physical Therapy, Sports Therapy and Rehabilitation
  • Orthopedics and Sports Medicine


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