FOREARM POSITION MATTERS DURING ECCENTRIC SHOULDER EXERCISES: AN EMG RECRUITMENT STUDY WITH IMPLICATIONS FOR
Corbin Hedt1, Bradley S Lambert1, Joshua Daum1
1Houston Methodist Orthopedics & Sports Medicine, Houston, TX, USA.
Background:
Eccentric exercise has demonstrated great utility in the rehabilitation of various shoulder pathologies. Research on the electromyographic (EMG) activity of the shoulder musculature during these activities is limited, however. Furthermore, no studies have observed how forearm positioning during exercise affects EMG output.
Purpose/Hypothesis:
The purpose was to examine the degree of specific muscle recruitment among commonly used eccentric exercises in rehabilitation of the upper extremity and shoulder. Secondarily, the authors hypothesized that different hand/forearm positions would alter EMG activity within the targeted musculature during a given exercise.
Study Design:
Prospective cross-sectional observation of EMG analysis.
Methods:
This study analyzed surface EMG data obtained from 10 healthy individuals during five eccentric exercises of the dominant extremity, performed in a randomized order: side-lying eccentric horizontal abduction (SL ER), half-kneeling weighted ball decelerations (BALL DC), seated eccentric external rotation in scaption (STD ER), standing eccentric external rotation at 0deg (STND ER), supine eccentric external rotation at 90deg (SUP ER). Each exercise was performed with two to three forearm position variants commonly used in clinical environments: neutral, pronation, and/or supination. EMG data were collected from the upper trapezius, infraspinatus, teres minor, latissimus dorsi, and anterior/middle/posterior deltoid. Data were analyzed for each individual exercise and within each muscle using a mixed-model ANOVA repeated across forearm position. Significant interactions were followed by a Bonferroni post-hoc test for pairwise comparisons. Effect size was calculated for all significant pairwise comparisons using a Cohen's d statistic.
Results:
Significant differences in EMG activity for the selected musculature exist between forearm positions for four of the five exercises and Cohen's d effect sizes 0.178 - 1.159.
Conclusion:
Specific eccentric shoulder exercises activate muscles of the shoulder complex differently based on forearm positioning.
Level Of Evidence:
Level 2.
Related Concept Videos
01:23Muscles of the Shoulder
Anterior Thoracic Muscles
The anterior thoracic muscles include the serratus anterior, subclavius, and...
01:16Muscles that Move the Forearm
Forearm Flexors
The biceps brachii, brachialis, and brachioradialis are forearm flexors. The biceps brachii is made up of two heads. Its long head originates at the supraglenoid tubercle of the scapula, whereas that of the short head is...
01:24Muscle Coordination and Action
Agonists
Agonist muscles, often called prime movers, are the primary muscles responsible for producing a specific movement....
01:31Muscles that Move the Arm
The pectoralis major has two origins. Its clavicular head originates on the medial half of the clavicle. In contrast, the sternocostal head originates on the costal cartilages of ribs 1-6, the sternum, and the aponeurosis of the external oblique of the...