Relationship between shoulder external rotation muscle strength in approximate zero position and thorax position during pitching motion

Abstract

The aim of this study was to investigate the relationship between shoulder external rotation (ER) muscle strength in the zero position (zero ER strength) and the thorax position at the shoulderʼs maximum exter nal rotation during the late cocking phase (MER).

A total of 14 healthy adult men participated in this study. Zero ER strength was measured using a handheld dy namometer with the shoulder in the zero position and the elbow in 90̊flexion. A three-dimensional motion capture system was used to assess the thorax angle（anteroposterior tilt angle and lateral tilt angle) at MER and maximum shoulder internal rotation moment (MIRM) and elbow varus moment (MVM). The relationship between zero ER strength and thorax angle and MIRM and MVM were calculated using Spearmanʼs rank correlation coefficient.

The zero ER strength positively correlated with the thorax anterior tilt angle (ρ=0.76, p=0.00015). Additionally,the zero ER strength negatively correlated with MIRM and MVM (ρ=­0.65, p=0.01; ρ=­0.56, p=0.03, respectively).

People with high zero ER strength values may have a large anterior tilt angle of the thorax during the throwing motion.