title: Effects of neuromuscular fatigue on the electromechanical delay of the leg extensors and flexors in young and old men.
abstract: OBJECTIVE
  The purpose of this study was to investigate the effects of a fatigue-inducing bout of submaximal, intermittent isometric contractions on the electromechanical delay (EMD) of the leg extensors and flexors in young and old men.
  
  
  METHODS
  Twenty young (mean ± SD: age = 25 ± 2.8 years) and sixteen old (age = 70.8 ± 3.8) recreationally active men performed maximal voluntary contractions (MVCs) followed by a fatigue-inducing protocol consisting of intermittent isometric contractions of the leg extensors or flexors using a 0.6 duty cycle (6 s contraction, 4 s relaxation) at 60 % of MVC until volitional fatigue. MVCs were again performed at 0, 7, 15, and 30 min post fatigue. A three-way mixed factorial ANOVA was used to analyze the EMD data.
  
  
  RESULTS
  There was a two-way muscle × time interaction (P = 0.039) where the EMD of the leg flexors was greater (P = 0.001-0.034) compared with baseline at all post fatigue time periods, but was only greater at immediately post fatigue for the extensors (P = 0.001). A significant two-way interaction for muscle × age (P = 0.009) revealed that the EMD was greater (P = 0.003) for the extensors for the old compared with the young men, but not different for the flexors (P = 0.506).
  
  
  CONCLUSIONS
  These findings showed differential fatigue-induced EMD recovery patterns between the leg extensors and flexors with the flexors being slower to recover and also that age-related increases of EMD are muscle group specific. The sustained increased EMD of the flexors during recovery may have important injury and performance implications in a variety of populations and settings.
authors.affiliation: Applied Musculoskeletal and Human Physiology Laboratory, Department of Health and Human Performance, Oklahoma State University, Stillwater, OK 74078, USA.
authors.forename: E C
authors.initials: EC
authors.lastname: Conchola
authors.forename: B J
authors.initials: BJ
authors.lastname: Thompson
authors.forename: D B
authors.initials: DB
authors.lastname: Smith
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D004576:Electromyography / Q000379:methods; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology