By Robbie Durand Generation Iron
Don’t slack on the reps.
Guys in the gym love to load up the calf machine and leg press and do half reps!! These are usually the same guys that have the skinniest legs and calves in the gym. Researchers from Italy examined the effect of range of motion at different loads on the electromyographic (EMG) activity during military press. Six experienced lifters performed 3 sets of 10 repetitions, each one with a different ROM: the first one with a final elbow angle of 90° (R1); the second with 135° (R2), and the last one with a final elbow angle of 180° (R3).
Basically, the 90 degree was a partial rep, the 135 degree angle was an incomplete or almost locked out position, and the 180 was a full range of motion from the bottom all the way till the arms were locked out. Not surprisingly, the execution of a complete ROM elicited the greatest deltoid EMG activity together with the trapezius showing their synergic activation.
There was a decrease of deltoid EMG activity together with a parallel decrease of the trapezius activity suggests not to perform the military press with partial elbow ROM, the Intermediate ROM (R2) where the elbow did not completely lock out does not reduce EMG activity of the deltoid but significantly reduces electrical activity of the upper traps.
So based on this study, using partial or intermediate reps is not going to fully activate the deltoids and trapezius muscle like doing a full range of motion. Using a full range of motion is going to activate more muscle fibers and lead to better muscle growth.
-Paoli A, Marcolin G, Petrone N. Influence of different ranges of motion on selective recruitment of shoulder muscles in the sitting military press: an electromyographic study. J Strength Cond Res. 2010 Jun;24(6):1578-83.