title: Muscle involvement during intermittent contraction patterns with different target force feedback modes.
abstract: OBJECTIVE
  Assess the effect of different feedback modes during intermittent contractions on primary and assessory muscle activity.
  
  
  BACKGROUND
  Intermittent contractions and physiological responses have been studied in laboratory settings. However, the feedback given to the subjects regarding timing and force level is generally not specified.
  
  
  METHODS
  Repeated measure design in which six subjects in randomized order performed two experimental conditions only differing in feedback mode.
  
  
  METHODS
  Intermittent static elbow flexion was performed against either a fixed-force transducer (visual feedback) or a weight to be held in position (proprioceptive feedback) both corresponding to 30% maximal voluntary contraction. Contraction and relaxation timing of 6 and 4 s, respectively, was shown on a VDU screen as colour code identical in both conditions.
  
  
  RESULTS
  Test contractions performed before and following 30 min of intermittent contractions showed larger fatigue development with proprioceptive feedback than visual feedback. Also rating of perceived exertion increased more during proprioceptive feedback than visual feedback. This may in part be explained by small differences in the mechanics during the two different feedback modes. In line with this, EMG recorded from four shoulder/arm muscles analyzed for amplitude and frequency showed similar activity initially; but later, during the 30 min contraction larger amplitudes were attained during proprioceptive feedback than visual feedback.
  
  
  CONCLUSIONS
  Feedback mode significantly effects the muscle involvement and fatigue during intermittent contractions. RelevanceIntermittent contractions are common in many work places and various feedback modes are being given regarding work requirements. The choice of feedback may significantly affect the muscle load and consequently the development muscle fatigue and disorders.
authors.affiliation: Institute of Sport Science and Clinical Biomechanics, University of Southern Denmark, Compusvej 55, 5230, Odense M, Denmark. gis@sportmed.sdu.dk
authors.forename: G
authors.initials: G
authors.lastname: Sjøgaard
authors.forename: L V
authors.initials: LV
authors.lastname: Jørgensen
authors.forename: D
authors.initials: D
authors.lastname: Ekner
authors.forename: K
authors.initials: K
authors.lastname: Søgaard
mesh_terms: D001696:Biomechanical Phenomena; D004551:Elbow Joint / Q000502:physiology; D004576:Electromyography; D005246:Feedback; D006801:Humans; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011434:Proprioception / Q000502:physiology