Effects of changes in muscle activation level and spine and hip posture on erector spinae fiber orientation

ABSTRACT Introduction: During lumbar flexion, the fiber orientation of the lumbar erector spinae (LES) muscle becomes oriented more along the spine compressive axis. It is unknown how changes in LES activation effect fiber orientation. Methods: Ultrasound images of LES were collected during 2 sets of experimental conditions: (1) varying levels of LES activation while lying prone; and (2) varying spine and hip angles while seated. Electromyographic activity and lumbar spine and hip angles were also recorded. Results: As LES activation increased, increases in fiber orientation (signifying increased orientation along the posterior shear axis) were found (P