Little 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: ~11% lower for seated barbell versus dumbbell (p = 0.038), ~15% lower in standing barbell versus dumbbell (p < 0.001), ~8% lower for seated versus standing dumbbells (p = 0.070); For medial deltoid, ~7% lower for standing barbell versus dumbbells (p = 0.050), ~7% lower for seated versus standing barbell (p = 0.062), 15% lower for seated versus standing dumbbell (p = 0.008); For posterior deltoid: ~25% lower for seated versus standing barbell (p < 0.001), ~24% lower for seated versus standing dumbbells (p = 0.002); For biceps, ~33% greater for seated barbell versus dumbbells (p = 0.002), 16% greater for standing barbell versus dumbbell (p = 0.074), ~23% lower for seated versus standing dumbbells (p < 0.001); For triceps, ~39% greater for standing barbell versus dumbbells (p < 0.001), ~20% lower for seated versus standing barbell (p = 0.094). 1-RM strength for standing dumbbells was ~7% lower than standing barbell (p = 0.002) and ~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.