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Modification of the serratus anterior strength test to reduce confounding muscle activation: An EMG-based validation
Christian Weber1, Tobias Goetschi2, Carl M Zipser3
1Department of Physiotherapy, Balgrist University Hospital, Forchstrasse 340, 8008, Zurich, Switzerland.
Objectives:
To compare the seated flexion strength test (FST) with two modifications incorporating shoulder external rotation and supine positioning, aiming to improve serratus anterior (SA) selectivity through reduced upper (UT) and lower trapezius (LT) interference.
Design:
Cross-sectional validation study using surface electromyography (EMG) and handheld dynamometry.
Setting:
University hospital musculoskeletal department.
Participants:
Eighteen healthy adults.
Main Outcome Measures:
EMG activation of SA, UT, LT and pectoralis major normalized to maximum voluntary contraction; activation ratios (UT/SA and LT/SA); force measurements with handheld dynamometer.
Results:
Both modifications significantly reduced UT (p = 0.002) and LT activation (p = 0.010-0.049) compared to the FST without significantly reducing SA activity. The ratios (median UT/SA, LT/SA) showed a non-significant trend toward reduction in modification 1 (0.53, 0.57) and modification 2 (0.60, 0.41) compared to the FST (0.83, 0.71). Only modification 2 demonstrated excellent reliability (ICC 0.97, 95 % CI:0.92-0.99, MDC 14 %).
Conclusions:
The modification 2 (supine positioning, shoulder external rotation, 45° tilted dynamometer) enhances SA isolation and demonstrates superior reliability compared to the FST. Therefore, it may improve clinical assessment of SA strength particularly when differentiating from UT and LT is of interest. Further research is needed before applying these findings to patient populations.
