Abstract
Alterations of scapular kinematics affect the whole kinematic chain, potentially leading to the impingement syndrome. This is crucial in overhead sports, where athletes perform frequent and quick upper limb actions. In this manuscript, we aimed to assess the extent to which fatigue alters scapulo-thoracic and scapulo-humeral ranges of motion (RoM), as well as scapulo-humeral movement onset during different upper limb actions. Twenty-four young healthy males aged 22 ± 2 years (height: 1.82 ± 0.06 m, body mass: 78.0 ± 7.8 kg) performed three movements (upper limb elevation, scapular-plane abduction, and intra-extra rotation) before and after an isokinetic fatigue protocol (upper limb intra/extra rotation, 32 repetitions at 120 degrees/s). Pre vs. post fatigue RoM of humeral elevation and rotation, scapular retraction/protraction, and rotation and tilt were computed. Humerus-scapula movement delay was also determined. Humerus elevation range reduced during intra/extra humerus rotation in fatigued conditions (p = 0.006). Scapular tilt RoM increased after the fatigue protocol (p = 0.063, large effect). Humerus-scapular movement onset delay reduced in fatigued conditions of about 80 ms (p < 0.001, large effect). In sum, fatigued intra/extra upper limb rotators altered the scapulohumeral rhythm, and joints RoM in movements outside the scapular plane. Rather, movements close to the scapular plane were less prone to fatigue-induced alterations.
Highlights
Shoulder girdle kinematics involves the synergic motion of three bones and the interaction of three joints, combined with a so called functional joint, which describes the rotation and sliding of the scapula on the thorax (Neumann, 2010; Lefèvre-Colau et al, 2018a,b)
Discrepancies between studies can be attributed to the degree of humeral elevation and the postural arrangement adopted in the fatigue protocols, the applied load or upper limb movement (Lawrence et al, 2019)
The scapulahumeral angles were computed as an YXY Euler sequence (Wu et al, 2005), and we considered humeral elevation and intra-extra rotation (Figures 1, 2)
Summary
Shoulder girdle kinematics involves the synergic motion of three bones (humerus, clavicle, and scapula) and the interaction of three joints (glenohumeral, sternoclavicular, and acromioclavicular), combined with a so called functional joint (scapulo-thoracic), which describes the rotation and sliding of the scapula on the thorax (Neumann, 2010; Lefèvre-Colau et al, 2018a,b). Especially in disciplines involving repeated overhead maneuvers, a premature or excessive rotation of the scapula during humerus elevation or lowering can induce abnormal sliding of the Fatigue Affects the Shoulder Dyskinesis humeral head. This in turn might lead to the impingement syndrome (Su et al, 2004; Chopp et al, 2011; Noguchi et al, 2013; Chopp-Hurley et al, 2016). Discrepancies between studies can be attributed to the degree of humeral elevation and the postural arrangement adopted in the fatigue protocols (prone, sitting or standing position), the applied load (bottle, elastic band, and sport-specific actions) or upper limb movement (elevation or abduction) (Lawrence et al, 2019)
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