title: Gender influence on fatigability of back muscles during intermittent isometric contractions: a study of neuromuscular activation patterns.
abstract: BACKGROUND
  Gender difference in the fatigability of muscles can be attributed to muscle mass (or strength) and associated level of vascular occlusion, substrate utilization, muscle composition, and neuromuscular activation patterns. The purpose of this study was to assess the role of neuromuscular activation patterns to explain gender differences in back muscle fatigability during intermittent isometric tasks.
  
  
  METHODS
  Sixteen males and 15 females performed maximal voluntary contractions (Strength) and a fatigue test to exhaustion (fatigue criterion=time to exhaustion), while standing in a static dynamometer measuring L5/S1 extension moment. The fatigue test consisted of repetitions of an 8-s cycle (1.5 s ramp to reach 40% of maximal voluntary contraction +5s plateau at 40% of maximal voluntary contraction +1.5s rest). Surface electromyography signals were collected bilaterally from 4 back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10).
  
  
  RESULTS
  Males were stronger (P<0.05) than females (316, SD 82>196, SD 25 Nm) but showed significantly shorter time-to-exhaustion values (7.1, SD 5.2<13.0, SD 6.1 min.), the latter result being corroborated by electromyographic indices of fatigue. However, the gender effect on time to exhaustion disappeared when accounting for Strength, thus supporting the muscle mass hypothesis. Among the various electromyographic indices computed to assess neuromuscular activation patterns, the amount of alternating activity between homolateral and between contralateral muscles showed a gender effect (females>males).
  
  
  CONCLUSIONS
  These results support the muscle mass hypothesis as well as the neuromuscular activation hypothesis to explain gender differences in back muscle fatigability.
authors.affiliation: Occupational Health and Safety Research Institute Robert-Sauvé, Montreal, Que., Canada H3A 3C2. lariviere.christian@irsst.qc.ca
authors.forename: Christian
authors.initials: C
authors.lastname: Larivière
authors.forename: Denis
authors.initials: D
authors.lastname: Gravel
authors.forename: Denis
authors.initials: D
authors.lastname: Gagnon
authors.forename: Phillip
authors.initials: P
authors.lastname: Gardiner
authors.forename: A
authors.initials: A
authors.lastname: Bertrand Arsenault
authors.forename: Nathaly
authors.initials: N
authors.lastname: Gaudreault
mesh_terms: D000328:Adult; D001415:Back / Q000502:physiology; D004576:Electromyography / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012737:Sex Factors