The Effects Of Hand Grip Force On Shoulder Muscle Activity At Different Angles Of Shoulder Range Of Motion In Patients With Shoulder Pain

ABSTRACT

In the present research study 4 shoulder muscles-the supraspinatus, infraspinatus, the middle deltoid and the upper part of the trapezius-were assessed for muscle thickness using real time ultrasonography (RUSI) in various degrees of abducted and flexed arm positions, in 30 patients with acute and sub-acute shoulder pain and 30 asymptomatic healthy subjects (N=60). The symptomatic and asymptomatic subjects were further subdivided according to affection of dominant (n=15) and non-dominant (n=15) shoulder joint. Muscle thickness (mm) was measured using real time ultrasonography of dominant and non-dominant shoulder in different range of movement of shoulder abduction and flexion in symptomatic patients and asymptomatic subjects with and without gripping action on the dynamometer. The subjects were asked to produce a static handgrip force of in 8 different arm positions. In all positions, the subjects held a dynamometer in the hand. The activity in the shoulder muscles was assessed using RUSI while the participating subjects produced a handgrip with maximal force. Muscle thickness and changes with activity was similar in symptomatic and asymptomatic individuals. Muscle activity increased in the middle deltoid muscle in humeral flexion and abduction from 0 0 through 800, whereas supraspinatus and lower trapezius showed increased muscle thickness only in the initial ranges of movement of shoulder flexion, whereas, infraspinatus did not show exhibit any significant change. Our findings imply that high static hand grip force, particularly in elevated arm positions, increases the load on some shoulder muscles, independent of presence of pain in the shoulder. Handgrip activity is important to evaluate while assessing shoulder load in manual work and in clinical evaluations of patients with shoulder pain. Also, while rehabilitation it would be possible to make use of hand gripping activity and load the shoulder muscles differently and distinctly throughout the ranges of movement of shoulder joint.