Effects of Body Position and Loading Modality on Muscle Activity and Strength in Shoulder Presses

Saeterbakken, AH and Fimland, MS. Effects of body position and loading modality on muscle activity and strength in shoulder presses. J Strength Cond Res 27(7): 1824-1831, 2013Little is known about the effect of performing upper-body resistance exercises with dumbbells versus barbells and standing versus seated. Therefore, this study sought to compare electromyogram activity (EMG) and one-repetition maximum (1-RM) in barbell and dumbbell shoulder presses performed seated and standing. Fifteen healthy men volunteered for 1-RM and EMG testing with a load corresponding to 80% of the 1-RM. Electromyogram activity was measured in the anterior, medial, and posterior deltoids and biceps and triceps brachii. The following EMG differences or trends were observed: For deltoid anterior: approximate to 11% lower for seated barbell versus dumbbell (p = 0.038), approximate to 15% lower in standing barbell versus dumbbell (p < 0.001), approximate to 8% lower for seated versus standing dumbbells (p = 0.070); For medial deltoid, approximate to 7% lower for standing barbell versus dumbbells (p = 0.050), approximate to 7% lower for seated versus standing barbell (p = 0.062), 15% lower for seated versus standing dumbbell (p = 0.008); For posterior deltoid: approximate to 25% lower for seated versus standing barbell (p < 0.001), approximate to 24% lower for seated versus standing dumbbells (p = 0.002); For biceps, approximate to 33% greater for seated barbell versus dumbbells (p = 0.002), 16% greater for standing barbell versus dumbbell (p = 0.074), approximate to 23% lower for seated versus standing dumbbells (p < 0.001); For triceps, approximate to 39% greater for standing barbell versus dumbbells (p < 0.001), approximate to 20% lower for seated versus standing barbell (p = 0.094). 1-RM strength for standing dumbbells was approximate to 7% lower than standing barbell (p = 0.002) and approximate to 10% lower than seated dumbbells (p < 0.001). In conclusion, the exercise with the greatest stability requirement (standing and dumbbells) demonstrated the highest neuromuscular activity of the deltoid muscles, although this was the exercise with the lowest 1-RM strength.