Aspects of shoulder function in relation to exposure demands and fatigue - a mini review

Abstract

Objective: To discuss the literature on control and function of multiple muscle systems with special focus on shoulder and upper extremity under submaximal conditions.

Design: The paper is a mini review based on 31 studies.

Background: Control mechanisms underlying the recruitment and gradation of muscle activity in complex multiple muscle systems during various voluntary exertions is still not fully understood. Load sharing principles may be influenced by several factors like work demand, fatigability, metabolic factors etc.

Methods: Several methods, e.g., electromyography, intramuscular pressure, and tissue oxygenation are used. The definition of fatigue is discussed.

Results and conclusion: A relatively fixed load sharing of the shoulder muscles has been found at low load levels, submaximal speeds and with a limited range of movements of the arms for healthy subjects. However, the load sharing of the shoulder muscles can be changed to some extent in response to fatigue, mental demands, visual feedback and in patients suffering from disorders in the upper extremities. It is hypothesized that lack of ability to redistribute muscle activation pattern in the shoulder region or the upper extremity increases the risk of development of work related symptoms.