title: Pelvic stabilization and semisitting position increase the specificity of back exercises.
abstract: OBJECTIVE
  To examine the effect of pelvic stabilization and two lower-limb configurations on the EMG activity of back and hip extensor muscles during a dynamic back extension exercise on a machine and to compare them between sexes.
  
  
  METHODS
  Twenty-two healthy volunteers (11 men and 11 women) performed five trunk flexion-extension cycles at 40% of their maximal voluntary contraction (MVC) in a machine designed for back exercise. Two different positions were used: 1) seated position (seat horizontal, knees at 90 degrees ) and 2) semisitting position (seat slightly tilted forward at 15 degrees , knees at 45 degrees of flexion). In each position, three pelvic stabilization conditions were tested: 1) unrestrained (control condition), 2) partially restrained (posteriorly), and 3) totally restrained (posteriorly and anteriorly). EMG signals were recorded bilaterally with 12 pairs of electrodes placed on back muscles as well as on the gluteus maximus and biceps femoris. The muscular activation level, that is, the percentage of EMG amplitude relative to the maximal EMG obtained from MVC, was used to asses the relative contribution of each muscle group across exercises.
  
  
  RESULTS
  In both sexes, two main results were found: 1) pelvic stabilization (partially and totally restrained) significantly (P < 0.05) increased the activity of all back muscles (average of 12%) and 2) semisitting position significantly decreased (range = 8-27%) the activity of two hip extensors compared with the seated position. Sex differences were also observed relative to the activity of some back muscles as well as the biceps femoris.
  
  
  CONCLUSIONS
  Combining pelvic stabilization and semisitting position in back exercise machines might be a useful way to localize the effects of endurance training at the back muscles and this in both the sexes.
authors.affiliation: Centre for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), Montreal Rehabilitation Institute, Montreal, Quebec, Canada.
authors.forename: Rubens A
authors.initials: RA
authors.lastname: da Silva
authors.forename: Christian
authors.initials: C
authors.lastname: Larivière
authors.forename: A Bertrand
authors.initials: AB
authors.lastname: Arsenault
authors.forename: Sylvie
authors.initials: S
authors.lastname: Nadeau
authors.forename: André
authors.initials: A
authors.lastname: Plamondon
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002081:Buttocks; D015331:Cohort Studies; D004576:Electromyography; D005260:Female; D006615:Hip / Q000502:physiology; D006801:Humans; D017116:Low Back Pain / Q000517:prevention & control; D008161:Lumbosacral Region / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D055070:Resistance Training / Q000379:methods*; D012737:Sex Factors; D055815:Young Adult