The purpose of this study was to determine biceps brachii electromyographic (EMG) activity during maximal
voluntary rotator actions of the shoulder at 45 and 90° of shoulder abduction. The EMG activity of the biceps brachii was
recorded in 17 healthy college students during maximal concentric and eccentric internal and external rotation of the
shoulder at 60 and 180°/s. Significantly higher EMG activity of the biceps was observed at 90 compared with 45° of
shoulder abduction during concentric (p<0.01) and eccentric external rotator action (p<0.001), at both isokinetic velocities.
The EMG activity of the biceps brachii was significantly higher during eccentric compared to concentric actions, for
both internal and external rotator actions regardless of arm position or isokinetic velocity (p<0.001) and during eccentric
internal rotator action at 180 compared to 60°/s at both 45 (p<0.01) and 90° (p<0.05) of shoulder abduction. The findings
of this study showed that biceps brachii was moderately active during voluntary isokinetic rotator actions of the elevated
arm, suggesting a potential function as a glenohumeral stabilizer.