The further you extend your arms when doing the neck-press, the more you stimulate the muscles in your shoulders. So the best way to do a neck-press is with free dumbbells, and not with a barbell or Smith machine. Italian sports scientists from the University of Padova write on the matter in the Journal of Strength and Conditioning Research.
The researchers did an experiment with 6 experienced male weight trainers. The men trained their shoulders by doing 3 different versions of the neck-press. The starting position was the same in all three versions [A]. In one exercise the men stretched their arms above their head to a 90-degree angle [B]. That was R1.
In exercise R2 the men extended their arms above their head to an angle of 135 degrees [C], and in R3 they extended their arms fully, to an angle of 180 degrees [D].
Before the men started doing the exercises, the researchers attached electrodes to their muscles, so they could measure how hard the men’s muscles had to work.
To cut a long story short: R2 was a better shoulder exercise than R1, and R3 was better than R2. The results were the same for all muscle groups that the researchers had attached an electrode to.
The figures below show the activity in the muscle groups when the men trained at 70 percent of their 1RM.
PMCH = upper part of the pecs; AD = anterior delt; MD = medial delt; PD = posterior delt.
UT = uppermost trapezius; MT = middle trapezius; TM = teres minor, TBLH = triceps.
The positive effect of a complete neck-press is stronger for the trapezius than for the delts. That’s why the researchers suspect that athletes who, for whatever reason, prefer to train with barbell need to devote more attention to their trapezius by doing other exercises.
J Strength Cond Res. 2010 Jun; 24(6): 1578-83.