The effect of isometric shoulder internal and external rotation on the acromiohumeral distance

This study aimed to determine the effect of isometric internal and external rotation at various degrees of shoulder abduction on the acromiohumeral distance (AHD).

This was a prospective study that used a within-subject repeated-measures design and randomization of independent variables. Data from 29 of 58 (40 women, 18 men) prospectively enrolled healthy subjects were used for analysis. A still ultrasound image of the right subacromial space was taken to measure the AHD for each of three contraction conditions (rest, isometric internal, and external rotation) at three shoulder positions (neutral and 30 and 45 degrees of abduction).

Intrarater reliability ranged from 0.86 to 0.99. At 45 degrees of shoulder abduction, the AHD was significantly smaller with isometric external rotation when compared with no contraction (P = 0.0015) and with isometric internal rotation (P = 0.0002).

The AHD was not affected by resistive isometric internal rotation of the shoulder, although it decreased with resistive isometric external rotation at 45 degrees of shoulder abduction. Resistive isometric shoulder external rotation in a position of abduction should be used with caution when the goal is to maintain the AHD. Further research is required to determine the effects of isometric contraction in patients with subacromial impingement syndrome.