title: Fluctuations in the skeletal muscle power-velocity relationship and interferon-γ after a muscle-damaging event in humans.
abstract: BACKGROUND
  Skeletal muscle power is velocity-dependent under constant load conditions. Interferon (IFN)-γ is an inflammatory cytokine that regulates skeletal muscle recovery following insult in experimental animals. It is unknown if the power-velocity relationship and IFN-γ are modulated after a muscle-damaging event in humans. Therefore, the purpose of this study was to identify the power-velocity relationship and circulating IFN-γ concentration responses to a muscle-damaging event in humans.
  
  
  METHODS
  Nine healthy males participated in this study. Each subject had one leg randomly assigned as the control leg. The other leg served as the treatment leg and performed an intense-stretch-shortening cycling (SSC) exercise protocol to induce muscle damage. To measure muscle damage and the power-velocity relationship, unilateral peak isometric force and power output (forces and velocities) measurements were performed prior to, immediately after, and during the days following the SSC protocol. The circulating IFN-γ concentrations were measured in serum samples obtained prior to, immediately after, and during the days following the SSC protocol. Statistical significance of single-leg isometric force and power output data were assessed using a two-way (time and leg treatment) analysis of variance (ANOVA) with repeated measures, followed by a Tukey's honestly significant difference (HSD) to test multiple pairwise comparisons. The statistical significance of the IFN-γ data were assessed using a one-way (time) ANOVA with repeated measures, followed by a Tukey's HSD to test multiple pairwise comparisons.
  
  
  RESULTS
  In the treatment leg, significant (P < 0.05) peak isometric force deficits occurred immediately and persisted several days after the SSC protocol, thereby identifying muscle damage-induced weakness. During muscle weakness in the treatment leg, peak power was significantly (P < 0.05) depressed and the velocities at peak power were significantly (P < 0.05) slower. Interestingly, circulating IFN-γ concentrations decreased at 2 and 3 days after compared to those immediately following the SSC protocol.
  
  
  CONCLUSIONS
  We conclude that the velocity to achieve a compromised peak power is reduced, and speculatively, the circulating IFN-γ excursion could be influential on the recovery of skeletal muscle after a muscle-damaging event in humans.
authors.affiliation: The Orthopedic Specialty Hospital, 5848 S Fashion Blvd, Murray, UT 84107, USA. tyler.barker@imail.org.
authors.forename: Tyler
authors.initials: T
authors.lastname: Barker
authors.forename: Vanessa T
authors.initials: VT
authors.lastname: Henriksen
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Martins
authors.forename: Carl R
authors.initials: CR
authors.lastname: Kjeldsberg
authors.forename: Harry R
authors.initials: HR
authors.lastname: Hill