Effect of Hand Position on EMG Activity of the Posterior Shoulder

Schoenfeld,B,Sonmez,RGT,Kolber,MJ,Contreras,B,Harris,R,
and Ozen, S. Effect of hand position on EMG activity of the
posterior shoulder musculature during a horizontal abductionexercise.J Strength Cond Res27(10): 2644-2649, 2013—The
reverse y machine is a popular exercise for strengthening the
horizontal shoulder abductors including the posterior deltoid.
There seems to be little consensus as to which hand position
most effectively targets the posterior deltoid despite this option
on most machines. This study investigated the impact of varying
one's hand position, and consequently altering shoulder joint
rotation, on muscle activity in various glenohumeral muscles dur-
ing exercise on the reverse y machine. Nineteen resistance-
trained men (mean age = 23.264.3 years; height = 176.967.1 centimeters; body mass = 81.3610.5 kilograms; body mass
index = 25.962.6) were recruited from a university population to
participate in the study. In a repeated measures design, subjects
grasped the hand bars on the machine with either a pronated
(PRO) or neutral (NEU) grip and performed dynamic horizontal
abduction repetitions to muscular failure using a load equating to
approximately 75% body weight. The order of performance of the
hand positions was counterbalanced between participants so
that approximately half of the subjects performed PRO rst and
the other half performed NEU rst. Surface electromyography
was used to record both mean and peak muscle activity of theposterior deltoid, middle deltoid, and infraspinatus. Results
showed that mean electromyography activity for the posterior
deltoid was signicantly greater in NEU compared with PRO
(p= 0.046; 95% CI = 0.1-7.4% maximal voluntary isometric
contraction). Similarly, mean electromyography activity of the
infraspinatus also was signicantly greater in NEU compared
with PRO (p= 0.002; 95% CI = 3.7-13.6% maximal voluntary
isometric contraction). The results of this study show that per-
forming exercise on the reverse y machine with a neutral hand
position signicantly increases activity of the posterior deltoid and
infraspinatus muscles compared with a PRO hand position.KEYWORDSreverse fly machine, internal rotation, external
rotation, neutral grip, pronated grip, glenohumeral muscles,
infraspinatus, middle deltoid, rear deltoid
INTRODUCTION