Original researchKinetic chain influences on upper and lower trapezius muscle activation during eight variations of a scapular retraction exercise in overhead athletes
Introduction
Scapular dyskinesis and related shoulder impingement syndrome are common conditions, particularly in overhead athletes.1 Although various muscles contribute to the three-dimensional movements around the shoulder, a lack of activity in the lower trapezius (LT) has been observed in these people, often in combination with an excessive upper trapezius (UT) activation.2 This might contribute to excessive clavicle elevation on the thorax coupled with increased anterior tilt at the scapulothoracic joint which causes the rotator cuff to impinge during elevation.3 The UT and LT muscles play different roles around the scapula during dynamic activities. Whereas the UT does not appear to have a line of action for being a substantive upward rotator in healthy persons, the LT assists in producing scapulothoracic upward rotation.4 Furthermore, evidence indicates that the LT acts as a stabilizer at the scapulothoracic joint.4 Consequently, scapular muscle exercises characterized by high LT and low UT muscle activation are of interest in the rehabilitation of patients with secondary impingement.
Training the activation and strength of selective muscle parts is the most common clinical approach in the management of musculoskeletal disorders. Depending on different stages of rehabilitation, various exercises might improve scapular muscle performance. In general, rowing and scapular retraction exercises have been found to enhance scapular muscle performance because of their preferential trapezius muscle activation.5, 6, 7 In addition, the scapular retracted position has been found to reduce symptoms and increase muscle performance in patients with impingement symptoms.8, 9
Recent guidelines have pointed to the value of integrating shoulder girdle exercises into a global functional kinetic chain for multiple reasons.10, 11 In general, these recommendations are based on the principle of sport specificity emphasizing the core as the center of the body during upper extremity training. Furthermore, it is assumed to increase the activity in particular shoulder muscles compared to more artificially stabilized positions such as the prone, side-lying or seated position. Maenhout et al. have recently investigated the influence of the position of the lower extremity on scapular muscle activity and balance during closed kinetic chain push-up variations.12 In their research, they discovered that contralateral leg extension stimulates LT activity during a knee push up plus exercise. However, the influence of proximal body segments during scapular retraction exercises integrating the trunk and lower extremity has not yet been investigated. Therefore, the purpose of this study was to analyze UT and LT muscle activation levels in an overhead athletic population during eight variations of a high scapular retraction movement. It was hypothesized that differences between UT and LT muscle activation would be found in all exercises and that the kinetic chain, influenced by lower extremity position or movement, would have an effect on these activation levels.
Section snippets
Methods
The data were obtained from a group of 30 healthy overhead athletes (17 male, 13 female), including volleyball and tennis players, and swimmers (mean ± SD age, 20 ± 3.5 years; mean ± SD weight, 69.4 ± 10.5 kg; mean ± SD body height, 179 ± 0.11 cm; mean ± SD BMI, 22 ± 0.02). The participants were recruited from the student population in the local metropolitan area. Twenty-seven were right-handed and 3 were left-handed, and it was the dominant shoulder that was tested. Athletes were included if they were between
Results
Means and standard deviations were calculated across participants for normalized EMG activity of each muscle for all exercises (Table 3). The ANOVA model revealed that sphericity could not be assumed, and a Greenhouse–Geisser correction was used to interpret all results. No three-way interaction was found with p < 0.05. Subsequently, two-way interactions including the factor “exercise” were of interest, but none of them showed significant results. So, in none of the exercises the muscle
Discussion
Particular retraction exercise variations might have an influence on the recruitment patterns of specific shoulder muscles. However, the conventional focus on individual joint training has resulted in a limited knowledge of scapular muscle recruitment during exercises that activate the entire kinetic chain system. Therefore, we investigated UT and LT muscle activation during eight kinetic chain variations of a high scapular retraction exercise which is thought to be relevant in the
Conclusion
In view of the recent tendencies with respect to functional kinetic chain training, we investigated UT and LT muscle activation during a series of eight variations of the high scapular retraction exercise. The results show higher LT compared to UT muscle activation in all exercises. We can conclude that standing in a squat position on the contralateral leg stimulates higher trapezius muscle activation levels compared to a seated performance of the exercise suggesting kinetic chain influences on
Practical implications
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Scapular retraction exercises seem useful for trapezius neuromuscular coordination training in overhead athletes because of their low upper trapezius muscle activation levels compared to those of the lower trapezius muscle.
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Several kinetic chain variations might be useful because none of them result in excessive upper trapezius activation in healthy athletes.
Acknowledgements
As there has been no financial support for this project, the authors are grateful to the volunteers who participated in this study.
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2019, Clinical BiomechanicsCitation Excerpt :One of the important points to be considered in exercise selection is the activation ratios between the trapezius muscle parts (Cools et al., 2007b). Exercises with lower UT/MT and/or UT/LT ratios are considered most appropriate for improving scapular muscle performance in painful shoulder conditions (Cools et al., 2007b; De Mey et al., 2013b; Moeller et al., 2014). We observed lower UT/MT and UT/LT ratios in Exercise 1, 2, and 5 performed at 0° shoulder abduction, and the lowest ratios were in Exercise 5.