Investigating women's chest size, trunk muscle co-contraction and back pain during prolonged standing.

BACKGROUND: Chest size is a known factor in the development of back pain for women. However, the neuromuscular mechanisms associated with chest size and back pain are poorly understood. OBJECTIVE: The purpose of this study was to investigate chest size and its association with back pain development and muscle activity patterns during prolonged standing. METHODS: Twenty university-aged women were divided into two groups: small chest size (n= 10, ∼A/C cup) and large chest size (n= 10, ∼D/E cup). Participants completed a 2-hr standing protocol, where eight channels of bilateral trunk electromyography were collected. Muscle activity, specifically co-contraction, was compared between chest size groups, pain developers, and time. RESULTS: The large chest size group reported higher amounts of pain at the upper, middle, and low back. Women in the large chest group sustained higher levels of co-contraction for muscles involving the thoracic and lumbar erector spinae compared to those in the small chest size group during prolonged standing. CONCLUSIONS: Thoracolumbar co-contraction determined in this study may be a potential mechanism contributing to increased back pain development for women with large chest sizes during prolonged standing. This pain mechanism could be targeted and addressed in future non-invasive musculoskeletal rehabilitation to improve back pain for women.