Activation levels of infraspinatus and posterior deltoid
Recently, various study have been conducted to establish exercises that most exclusively target the scapulothoracal and rotator cuff muscles. During shoulder external rotation, both the infraspinatus as well as the posterior deltoid muscle are activated. Although there is ample evidence pointing towards benefits of closed kinetic chain exercises early in rehabilitation, most infraspinatus strenghtening exercises are performed in an open chain.
This study employed surface EMG to record muscle activation levels of the infraspinatus and the posterior deltoid in 15 healthy male subjects during external rotation in an open kinetic chain and a closed kinetic chain condition. Muscle activity was normalized using the maximum voluntary isometric contraction and the ratio of infraspinatus to posterior deltoid activity was calculated.
The closed chain condition elicited significantly higher infraspinatus activation levels than the open chain condition. The posterior deltoid activation levels on the other hand were significantly decreased when the exercises were performed in a closed chain. Moreover, the infraspinatus:posterior deltoid activation ratio was significantly higher in the closed kinetic chain condition.
> From: Kang et al., J Phys Ther Sci 26 (2015) 895-897. All rights reserved to The Society of Physical Therapy Science. Click here for the Pubmed summary.