Effect Of Trunk Rotation On Glenohumeral Internal And External Rotator Peak Torque

Overhead sport activities, such as throwing, impose considerable stress on glenohumeral internal and external rotators (GHIR and GHER), potentially causing injury over time. These forces are often placed on the shoulder with the trunk in a rotated position. PURPOSE: The purpose of this study was to determine the effect of trunk rotation on isometric (ISO) and concentric (CON) peak torque production of the GHIR and GHER muscles. METHODS: Thirteen subjects (6F, 7 M; 21.8 ± 1.8 yo; 1.7 ± 0.1 m; 74.2 ± 12.1 kg) were recruited and granted informed consent to participate in this IRB approved study. All subjects were free of upper extremity musculoskeletal injuries for the past 3 months. ISO and CON peak torque were collected using a Biodex Isokinetic Dynamometer (System 4 Pro, Biodex Medical Systems) at 0, 15, and 30 degrees of trunk rotation. Subjects were positioned with the dominant shoulder abducted to 90 degrees with 90 degrees of elbow flexion. Following a familiarization, all subjects performed maximum GHER and GHIR ISO contractions at 0, 15, and 30 degrees of trunk rotation. Subjects then performed 5 CON repetitions each for GHIR and GHER at 60 and 180 degrees per second and in all 3 trunk rotation positions. All conditions were randomized, and subjects received 1 minute of rest following each trial. Peak forces were recorded, and SPSS 29 (IBM SPSS Statistics, USA) was used to perform a repeated-measures ANOVA to determine differences in peak torque between trunk positions for isometric and concentric contractions. RESULTS: There was a significant difference in ISO GHER peak torque between the 3 trunk positions (F (1.263, 15.155) = 5.972, p = 0.02). A post hoc pairwise comparison with Bonferroni correction revealed a significant decrease in ISO GHER peak torque between 0 degrees and 30 degrees of trunk rotation, 20.0 and 17.1 ft-lbs respectively (p = 0.05) and between 15 degrees and 30 degrees of trunk rotation, 18.8 and 17.1 ft-lbs respectively (p = 0.02). There was no significant difference for all other ISO and CON conditions. CONCLUSIONS: Increased trunk rotation leads to a decrease in ISO GHER peak torque production. While trunk rotation does not appear to influence peak torque for ISO GHIR or either CON condition, it may be appropriate to strengthen the GHER pattern in multiple trunk positions for overhead athletes.