Objectives: To measure the strain on 3 fiber groups of the subscapularis muscle at various glenohumeral joint positions and to determine the appropriate shoulder position for subscapularis muscle stretching. Design: Repeated-measures design. Setting: Biomechanics laboratory. Specimens: Nine frozen-thawed glenohumeral joints obtained from 9 fresh cadavers. Interventions: Not applicable. Main Outcome Measure: The strain on the upper, middle, and lower fiber groups of the subscapularis were measured by precise displacement sensors during 14 different glenohumeral joint positions. Results: The glenolmmeral joint position that showed the largest strain varied among the 3 fiber groups. Although no position showed significantly large strain on the upper and middle fiber groups, external rotation at 30 degrees, 60 degrees, and 90 degrees of elevation, abduction, flexion, and horizontal abduction revealed significantly greater strain on the lower fiber groups (P<.005). Additionally, except for external rotation at 0 degrees of elevation, the strain on the lower fiber group was significantly greater than that on the upper and middle fiber groups in external rotation (P<.005). Conclusions: The stretching position of each fiber group of the subscapularis differs depending on the glenohumeral joint position. External rotation at 30 degrees to 60 degrees of glenohumeral elevation, abduction, flexion, and horizontal abduction can significantly stretch the lower fiber group of the subscapularis muscle.