Original articleThe effects of muscle fatigue on scapulothoracic joint position sense and neuromuscular performance
Introduction
The scapulothoracic joint comprises a mobile scapula moving on the relatively fixed rib cage, which links the upper extremity to the axial skeleton and provides the proximal stability for the glenohumeral joint (Ludewig et al., 2009). The scapulothoracic articulation lacks a joint capsule and surrounding ligamentous tissues, so its stability is contributed by muscles attaching to it, including the upper and lower trapezius (UT and LT), and serratus anterior (SA) etc. The scapula has a bony connection to the thorax via the clavicle and this provides some constraints to the scapulothoracic movements (Deng and Shih, 2015; Voight and Thomson, 2000). Proper scapular sensorimotor control is crucial for adequate proximal stability for the shoulder (Paine and Voight, 1993). Altered scapular sensorimotor control, presented as changes in scapular alignment and muscle activation (Kibler, 1998; Kibler and McMullen, 2003; Kibler and Sciascia, 2010), has been linked with various shoulder dysfunctions such as shoulder impingement or instability (Hsu et al., 2009; Lin et al., 2005; Michener et al., 2003).
The sensorimotor system receives and processes peripheral sensory inputs for joint function (proprioception), and produces appropriate motor responses (Guo et al., 2011; Myers et al., 2006; Tripp et al., 2006). The sensory inputs of the scapulothoracic joint mainly comes from the receptors of surrounding muscles and skin (Castelein et al., 2017). Muscle fatigue has been thought to have an influence on proprioception (Myers et al., 1999) and neuromuscular performance of the shoulder complex including decreased posterior tilt and lateral rotation of the scapula (Borstad et al., 2009), which might expose individuals to greater risks of developing injuries. Various fatigue protocols targeted at shoulder muscles have shown to have certain influences on scapular kinematics, but no consistent pattern of changes could be identified (Serenza et al., 2018; Szucs et al., 2009; Takasaki et al., 2016). Other researchers revealed that fatigued shoulder rotators impaired the shoulder reposition accuracy (Iida et al., 2014; Lee et al., 2003; Myers et al., 1999). Borstad et al. (2009) used modified push-ups as the fatigue protocol and found that after fatigue, the scapula showed more internal rotation and anterior tilt during arm elevation. Only one study has tried to identify the effect of muscle fatigue (induced by repetitive shoulder internal rotation movement) on scapulothoracic proprioception and found no difference in scapulothoracic reposition accuracy after shoulder internal rotators fatigue (Guo et al., 2011).
Because little was known regarding the effect of muscle fatigue on scapulothoracic neuromuscular performance and proprioception, the purpose of this study was to explore the effects of scapular muscle fatigue on the joint position sense and neuromuscular control of the scapulothoracic joint. The hypothesis of the study was that the joint reposition sense would be impaired after muscle fatigue, increasing the joint reposition errors and altering the neuromuscular performance of the scapula (including increased muscle activation, and decreases in scapular posterior tilt and lateral rotation) during scaption.
Section snippets
Participants
This was a cross-sectional, exploratory study. Thirty healthy participants were enrolled (15 males and 15 females, 23.5 ± 1.8 years, 167.6 ± 8.3 cm, 59.3 ± 8.5 kg). The sample size estimation was based on a pilot study of 10 subjects which showed that at least 26 participants were required to detect a difference in scapular posterior tilt with a significance level of 0.05 and a power of 0.80. The inclusion criteria were: (1) aged between 20 andto 40 years old; (2) no pain around neck, shoulder,
Results
Our protocol successfully fatigued the scapular muscles (22 fatigued UT; 17 fatigued LT; 19 fatigued SA). Ten people fatigued all three scapular muscles, and eight and 12 people fatigued two and one scapular muscles respectively. The averaged median frequency drop was 26.2% for the UT, 24.8% for the LT, and 23.5% for the SA. After the fatigue task, the measured force output for the UT and SA showed significant decreases (UT: 2.3 ± 1.1 N to 2.1 ± 1.1 N, p = 0.037; SA: 1.0 ± 0.4 N to 0.8 ± 0.4 N,
Discussion
The purpose of the current study is to examine the effects of scapular muscle fatigue on proprioception and neuromuscular control of the scapulothoracic joint. We hypothesized that scapular muscle fatigue would increase the joint reposition errors, decrease scapular posterior tilt and lateral rotation, and increase muscle activation. Our findings only supported our hypotheses partly that scapular muscle fatigue had an influence on scapular kinematics and serratus anterior muscle activity.
This
Conclusion
Scapular muscle fatigue did not influence the scapulothoracic joint position sense performance, but resulted in an altered activation of the serratus anterior muscle and undesired scapular kinematic changes (less posterior tilt and more protraction) between 90 and 120 degrees of arm elevation in the scapular plane. These kinematic changes should be closely monitored in individuals exposed to scapular fatiguing activities. Whether or not training of scapular muscles would delay or prevent the
Ethical approval
The protocol of this study was approved by the Institutional Review Board of National Yang Ming University (YM105067E), registered at ClinicalTrials.gov (NCT03066102), and was conducted at Taipei Veterans General Hospital and National Yang-Ming University.
Funding
This study was supported by Ministry of Science and Technology, Taiwan (MOST 106-2410-H-010 -012 -MY2).
Declaration of competing interest
All authors state that they do not keep any commercial, financial or personal relationships which may lead to a conflict of interests that could inappropriately influence their work. No research grant sponsor had any involvement in the study design; in the collection, analysis and interpretation of data; in the writing of the manuscript; or in the decision to submit the manuscript for publication.
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