Muscle involvement during intermittent contraction patterns with differenttarget force feedback modes

Objective. Assess the effect of different feedback modes during intermitten t 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. Design. Repeated measure design in which six subjects in randomized order p erformed two experimental conditions only differing in feedback mode. Methods. Intermittent static elbow flexion was performed against either a f ixed-force transducer (visual feedback) or a weight to be held in position (proprioceptive feedback) both corresponding to 30% maximal voluntary contr action. Contraction and relaxation timing of 6 and 4 s, respectively, was s hown on a VDU screen as colour code identical in both conditions. Results. Test contractions performed before and following 30 min of intermi ttent contractions showed larger fatigue development with proprioceptive fe edback than visual feedback. Also rating of perceived exertion increased mo re during proprioceptive feedback than visual feedback. This may in Dart be explained by small differences in the mechanics during the two different f eedback modes. In line with this, EMG recorded from four shoulder/arm muscl es analyzed for amplitude and frequency showed similar activity initially; but later, during the 30 min contraction larger amplitudes were attained du ring proprioceptive feedback than visual feedback. Conclusions. Feedback mode significantly effects the muscle involvement and fatigue during intermittent contractions.