Joint angle-dependence of elbow flexor activation levels during isometric and isokinetic maximum voluntary contractions

Objective. The influences of elbow joint angle and the type of contraction on the activation levels of biceps brachii and brachioradialis during maxim um voluntary isometric and isokinetic contractions were investigated. Design. A within-session repeated measures design. Background. Activation of synergistic elbow flexor muscles has been reporte d to be affected disparately by elbow joint angle and contraction type. Methods. Ten subjects performed concentric isokinetic, eccentric isokinetic , and isometric maximum voluntary contractions of the elbow flexor muscles. For the isokinetic contractions the activation levels of two ranges of mot ion were compared. For the isometric contractions the activation levels at two joint angles were compared. The activation levels of the biceps brachii and brachioradialis acquired simultaneously using bipolar surface electrod es and a surface electrode array were compared. Results. Results from the electrode array were similar to those acquired us ing conventional bipolar electrodes. The activation of biceps brachii was s ignificantly affected by joint angle during concentric isokinetic and isome tric maximum voluntary contractions. The activation of brachioradialis was significantly affected by joint angle only during eccentric isokinetic maxi mum voluntary contractions. Conclusions. The results confirm that joint angle and contraction type cont ribute to the distinction between the activation of synergistic elbow flexo r muscles during isometric and isokinetic contractions.