Shoulder Muscle Activation of Novice and Resistance Trained Women during Variations of Dumbbell Press Exercises

Previous research has compared the effects of trunk inclination angle on muscle activation using barbells and Smith machines in men. Whether similar effects occur with the use of dumbbells or in women remains unknown. The purpose was to compare upper extremity surface electromyographical (EMG) activity between dumbbell bench, incline, and shoulder presses. Dominate arm EMG data were recorded for collegiate-aged female resistance trained individuals ( ) and novice female resistance trained exercisers ( ) from which average EMG amplitude for each repetition phase (concentric, eccentric) was computed. No significant differences were found between experienced and novice resistance trained individuals. For the upper trapezius and anterior deltoid muscles, shoulder press activation was significantly greater than incline press which in turn was significantly greater than bench press across both phases. The bench and incline presses promoted significantly greater pectoralis major sternal activation compared to the shoulder press (both phases). While pectoralis major clavicular activation during the incline press eccentric phase was significantly greater than both the bench and shoulder presses, activation during the bench press concentric phase promoted significantly greater activation than the incline press which in turn was significantly greater than the shoulder press. These results provide evidence for selecting exercises in resistance and rehabilitation programs. 1. Introduction Variations of the bench press are commonly used weight training exercises for strength and power development of the muscles in and around the chest and shoulder areas. For example, although the bench press is most often performed with a standard barbell and stable flat bench, dumbbells and machines can also be used as sources of resistance along with unstable surfaces (i.e., cushions and Swiss balls) to produce similar press actions with varying intensity and stabilization demands. Understanding the mechanical demands imposed by each bench press variation assists with matching the patient/client needs with the specific characteristics of each exercise he/she completes. Changing the angle of trunk inclination during variations of bench pressing exercises changes the line of action of the resistance relative to the trunk and, in turn, changes the direction of the movement force provided by the shoulder muscles. Based on the arrangement of the shoulder muscles, accommodation to these changes in bench inclination is thought to promote maximal activation of the muscles active during