Associations between cervical and scapular posture and the spatial distribution of trapezius muscle activity

Abstract

The first aim of this investigation was to quantify the distribution of trapezius muscle activity with different scapular postures while seated. The second aim of this investigation was to examine the association between changes in cervical and scapular posture when attempting to recruit different subdivisions of the trapezius muscle. Cervical posture, scapular posture, and trapezius muscle activity were recorded from 20 healthy participants during three directed shoulder postures. Planar angles formed by reflective markers placed on the acromion process, C7, and tragus were used to quantify cervical and scapular posture. Distribution of trapezius muscle activity was recorded using two high-density surface electromyography (HDsEMG) electrodes positioned over the upper, middle, and lower trapezius. Results validated the assumption that directed scapular postures preferentially activate different subdivisions of the trapezius muscle. In particular, scapular depression was associated with a more inferior location of trapezius muscle activity (r=0.53). Scapular elevation was coupled with scapular abduction (r=0.52). Scapular adduction was coupled with cervical extension (r=0.35); all other changes in cervical posture were independent of changes in scapular posture. This investigation provides empirical support for reductions in static loading of the upper trapezius and improvements in neck posture through verbal cueing of scapular posture.

Keywords: Cervical posture; High-density EMG; Scapular posture; Trapezius muscle.

Conflict of interest statement

Conflict of interest

None.

Copyright © 2014 Elsevier Ltd. All rights reserved.

Figures

Fig. 1.

Reflective marker placement used to track cervical and scapular postures during three anatomically directed test positions: (a) anterior view, (b) posterior view, and (c) high-density surface EMG (HDsEMG) electrode array placement to record changes in the distribution of trapezius muscle activity across three test positions.

Fig. 2.

(a) Schematic of HDsEMG electrode array with position on trapezius. Array placement was normalized across all participants using a superior array with the 4th row placed along the C7-acromion line. (b) Example of topographical map (interpolation by a factor of 8) of 51 bipolar average rectified values of superior array, showing the center of gravity (white dot) and innervation zone (oval).

Fig. 3.

Three postures were measured during the experiment: (a) cervical posture (θCV) where positive angle indicates cervical flexion and negative angle indicates cervical extension; (b) scapular elevation/depression (θEL) where positive angle indicates scapular elevation and negative angle indicates scapular depression; (c) scapular abduction/adduction (θAB) where positive angle indicates scapular abduction and negative angle indicates scapular adduction. A local coordinate system origin was defined by a marker placed on the C7 vertebrae.

Fig. 4.

Example of data window used to obtain every dependent variable (averaged across 10–25 s). Scapular elevation (θEL) and the distribution of trapezius muscle activity in the superior–inferior direction (YCOG) during scapular elevation for a representative subject.

Fig. 5.

Mean (SD) change in trapezius muscle activity in the (a) medial–lateral direction (ΔXCOG), (b) inferior–superior direction (ΔYCOG), (c) cervical flexion/extension (ΔθCV), (d) scapular elevation/depression (ΔθEL), and (e) scapular abduction/adduction (ΔθAB) with respect to the coached neutral posture during three anatomically directed test positions. A value of zero indicates a variables value during coached neutral posture. * Indicates a statistically significant difference from neutral posture (P < 0.05). φ Indicates a statistically significant difference between postures (P < 0.05).

Fig. 6.

Correlation between (a) cervical posture (ΔθCV) and scapular abduction/adduction (ΔθAB) and (b) distribution of trapezius muscle activity in the inferior–superior direction (ΔYCOG) and scapular elevation/depression (ΔθEL). All data were referenced to the coached neutral posture and are grouped according to the three anatomically directed test positions (scapular elevation, scapular adduction, and scapular adduction and depression).