Scapulothoracic kinematic pattern in the shoulder pain and scapular dyskinesis: A principal component analysis approach

The relationship between shoulder pain and scapular dyskinesis (SDK) is unclear. Differences between groups with and without SDK have been demonstrated, focusing on the amount of scapular motion at specific degrees of humeral elevation. However, this approach does not consider the temporal information and shape of the scapular motion temporal series. Principal Component Analysis (PCA) may clarify this variability and advance current understanding of ‘abnormal’ movement patterns. This study aimed to evaluate the scapular kinematics in patients with shoulder pain and in asymptomatic participants with and without SDK using PCA. Data were collected in 98 participants separated in four groups: Pain + SDK (n = 24), Pain (n = 25), No Pain + SDK (n = 24), and No Pain (n = 25). Scapulothoracic kinematic data were measured with an electromagnetic tracking device during arm elevation and lowering phases. PCA and analysis of variance were used to compare the groups. The No Pain + SDK group had a progressive increasing in anterior tilt over the elevation phase compared to the Pain (effect size = 0.79) and No Pain (effect size = 0.80) groups. During the arm-lowering, the Pain + SDK group had a progressive increasing in anterior tilt over this phase in comparison to the No Pain + SDK group (effect size = 0.68). Therefore, PCA demonstrated differences in the scapular anterior tilt related to SDK and shoulder pain. The presence of SDK revealed a scapular pattern with progressive increasing in anterior tilt over the elevation phase. However, during the arm-lowering phase, asymptomatic participants with SDK changed their motion pattern, unlike the symptomatic group, reinforcing the suggested association between scapular modifications and shoulder symptoms.     

Rotator cuff tendinopathy alters the muscle activity onset and kinematics of scapula

Athletes with rotator cuff (RC) tendinopathy demonstrate an aberrant pattern of scapular motion which might relate to deficits in the scapular muscles. This study aimed to determine whether alteration in scapular kinematics is associated with deficits in the activity onset of scapular muscles. Forty-three male volleyball players (17 asymptomatic and 26 with RC tendinopathy) joined the study. Three-dimensional scapular kinematics was quantified using an acromial marker cluster method. The activity onset of the upper (UT), middle (MT), and lower trapezius (LT), and serratus anterior (SA) during arm abduction was assessed with electromyography. Athletes with RC tendinopathy demonstrated less scapular upward rotation (6.6 ± 2.3 vs. 8.2 ± 1.1°, p = 0.021) in the early phase of shoulder abduction from 0° to 30° when compared to asymptomatic athletes. The tendinopathy group had delayed activity onset of LT (14.1 ± 31.4 ms vs. 74.4 ± 45.1 ms, p < 0.001) and SA (−44.9 ± 26.0 ms vs. 23.0 ± 25.2 ms, p < 0.001) relative to UT when compared to the asymptomatic group. In asymptomatic athletes, earlier activity onset of MT and LT relative to UT was associated with more scapular upward rotation during 0–30° of abduction (r = 0.665, p = 0.021) and 30–60° of abduction (r = 0.680, p = 0.015), respectively. Our findings showed the control of the scapular upward rotation is related to the activity onset of the scapular muscles in athletes.     

Validity and reliability of 3D marker based scapular motion analysis: A systematic review

Methods based on cutaneous markers are the most popular for the recording of three dimensional scapular motion analysis. Numerous methods have been evaluated, each showing different levels of accuracy and reliability. The aim of this review was to report the metrological properties of 3D scapular kinematic measurements using cutaneous markers and to make recommendations based on metrological evidence.     

Effects of scapular upward rotation exercises on alignment of scapula and clavicle and strength of scapular upward rotators in subjects with scapular downward rotation syndrome

The purpose of this study was to investigate the effects of a 6-week scapular upward rotation exercise (SURE) on scapular and clavicular alignment and scapular upward rotators strength in subjects with scapular downward rotation syndrome (SDRS). Seventeen volunteer subjects with SDRS were recruited from university populations. The alignment of the scapula and clavicle was measured using radiographic analysis and compared in subjects before and after a 6-week self-SURE program. A hand-held dynamometer was used to measure the strength of the scapular upward rotators. The subjects were instructed how to perform the self-SURE program at home. The 6-week self-SURE program was divided into two sections (the first section with non-resistive SURE during weeks 1–3, and the second section with resistive SURE using thera-band during weeks 4–6). The significance of the difference between pre- and post-program was assessed using a paired t-test, with the level of statistical significance set at p < 0.05. Significant differences between pre- and post-program were found for scapular and clavicular alignment (p < 0.05). Additionally, the comparison between pre- and post-program measurements of the strength of the scapular upward rotators showed significant differences (p < 0.05). The results of this study showed that a 6-week self-SURE program is effective for improving scapular and clavicular alignment and increasing the strength of scapular upward rotator muscles in subjects with SDRS.     

Effects of horizontal shoulder abduction and adduction on the activity and strength of the scapular protractors

Increased activity of the serratus anterior (SA) muscle combined with decreased activity of the pectoralis major (PM) muscle during scapular protraction exercise is a widely used method for selective strengthening of the former muscle. However, the role played by the PM during maximal scapular protraction remains unclear. The objective of our study was to investigate the effects of horizontal shoulder abduction (decreasing PM activity) and adduction (increasing activity) on the strength and activity of the scapular protractors (the SA and PM) during maximal protraction. Twenty-nine healthy males performed maximal scapular protraction combined with horizontal shoulder abduction or adduction. The strength and activity of the PM and SA decreased significantly (both p < 0.01) during maximal scapular protraction combined with horizontal shoulder abduction, compared with maximal scapular protraction alone, but increased significantly (both p < 0.01) when maximal scapular protraction was combined with horizontal shoulder adduction. We thus conclude that the PM stabilizes the activated SA during maximal scapular protraction, which effectively increases SA activity and scapular protraction strength in the serratus punch posture.     

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

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.     

Objective classification of scapular kinematics in participants with movement faults of the scapula on clinical assessment

The aim of this study was to assess the potential of employing a classification tool to objectively classify participants with clinically assessed movement faults (MFs) of the scapula. Six participants with a history of shoulder pain with MFs of the scapula and 12 healthy participants with no movement faults (NMFs) performed a flexion movement control test of the scapula, while scapular kinematic data were collected. Principal component scores and discrete kinematic variables were used as input into a classifier. Five out of the six participants with a history of pain were successfully classified as having scapular MFs with an accuracy of 72%. Variables related to the upward rotation of the scapula had the most influence on the classification. The results of the study demonstrate the potential of adopting a multivariate approach in objective classification of participants with altered scapular kinematics in pathological groups.     

Electromyographic analysis of the serratus anterior and trapezius muscles during push-ups on stable and unstable bases in subjects with scapular dyskinesis

The present study was performed to assess the electromyographic activity of the scapular muscles during push-ups on a stable and unstable surface, in subjects with scapular dyskinesis. Muscle activation (upper trapezius [UT]; lower trapezius [LT]; upper serratus anterior [SA_5th]; lower serratus anterior [SA_7th]) and ratios (UT/LT; UT/SA_5th; UT/ SA_7th) levels were determined by surface EMG in 30 asymptomatic men with scapular dyskinesis, during push-up performed on a stable and unstable surface. Multivariate analysis of variance with repeated measures was used for statistical analyses. The unstable surface caused a decrease in the EMG activity of the serratus anterior and an increase in EMG activity of the trapezius (p = 0.001). UT/SA_5th and UT/ SA_7th ratios were higher during unstable push-ups (p = 0.001). The results suggest that, in individuals with scapular dyskinesis, there is increased EMG activity of the trapezius and decreased EMG activity of the serratus anterior in response to an unstable surface. These results suggest that the performance of the push up exercise on an unstable surface may be more favorable to produce higher levels of trapezius activation and lower levels of serratus anterior activation. However, if the goal of the exercise program is the strengthening of the SA muscle, it is suggested to perform the push up on a stable surface.     

Differences in scapular kinematics and scapulohumeral rhythm during elevation and lowering of the arm between typical children and healthy adults

Scapular kinematics in healthy adults is well described in the literature but little is known on typical children. This study aimed to compare the three-dimensional (3-D) scapular kinematics and scapulohumeral rhythm during the elevation and lowering of the arm in the scapular plane in typical children and healthy adults. Twenty-six healthy adults (35.34 ± 11.65 years, 1.70 ± 0.10 m, 70.00 ± 12.30 kg) and 33 typical children (9.12 ± 1.51 years, 1.40 ± 0.10 m, 35.40 ± 10.45 kg) participated in this study. 3-D scapular kinematics were obtained using an electromagnetic tracking device. The subjects were asked to elevate and lower their arm in the scapular plane. Children showed less scapular protraction compared to adults at 120° during arm elevation, more anterior tilt than adults in the elevation and also at 60°, 90° and 120° during lowering of the arm. Children also showed higher scapulohumeral rhythm during lowering of the arm compared to adults from 90° to 60°. It was also found a low to little correlation between scapular position and age. The study showed small but significant differences in scapular kinematics and scapulohumeral rhythm between children and adults. These results can help clinicians to improve diagnosis and treatment protocols directed to children with dysfunction, as reference values on scapular kinematics in healthy children are also provided in this study.     

Effects of trunk rotation on scapular kinematics and muscle activity during humeral elevation

Trunk rotation often accompanies humeral elevation, during daily activities as well as sports activities. Earlier studies have demonstrated that changes in spinal posture contribute to scapular motion during humeral elevation. However, the effect of trunk rotation on scapular kinematics during humeral elevation has received scant attention. This study aimed to clarify how trunk rotation affects scapular kinematics and muscle activities during humeral elevation. Electromagnetic motion capture and electromyography were used to assess scapular and clavicular motion and muscle activity in the right and left sides of 12 healthy young men. The subjects were seated and instructed to elevate both arms with the trunk in neutral, ipsilaterally rotated, or contralaterally rotated position. Ipsilaterally rotated trunk position decreased the internal rotation (by 5°, relative to neutral trunk position) and increased the upward rotation (by 4°, relative to neutral trunk position) of the scapula. Trunk position did not affect clavicular motion during humeral movement. Electromyography showed that contralaterally rotated trunk position increased the activity of the upper trapezius and serratus anterior muscles and decreased the activity of the lower trapezius. Therapists should consider the importance of trunk rotation, which may be the key to developing more efficient rehabilitation programs.     

The influence of hip strength on gluteal activity and lower extremity kinematics

The effects of hip muscle strength and activation on anterior cruciate ligament injury biomechanics, particularly knee valgus loading, have been reported in isolation and with equivocal results. However, the combination of these factors influences joint biomechanics. This investigation evaluated the influence of hip strength on gluteal activation and knee valgus motion. Maximal isometric hip abduction (ABD) and external rotation (ER) contractions were used to define High and Low strength groups. Knee kinematics and gluteus maximus (GMax) and medius (GMed) EMG amplitudes obtained during landing were compared between High and Low strength groups after controlling for the potential confounding influence of sex. Knee valgus motion did not differ between the High and Low hip ABD and ER strength groups. However, the Low ABD and ER strength groups displayed greater GMed and GMax EMG amplitudes, respectively, compared to the High strength groups. These findings suggest that weaker individuals compensate for a lack of force production via heightened neural drive. As such, hip muscle strength influences knee valgus motion indirectly by determining neural drive requirements.     

The recruitment order of scapular muscles depends on the characteristics of the postural task

Previous studies show that the scapular muscle recruitment order could possibly change according to the characteristics of the postural task. We aimed to compare the activation latencies of serratus anterior (SA), upper, middle, and lower trapezius (UT, MT and LT, respectively) between an unpredictable perturbation (sudden arm destabilization) and a predictable task (voluntary arm raise) and, to determine the differences in the muscle recruitment order in each task. The electromyographic signals of 23 participants were recorded while the tasks were performed. All scapular muscles showed earlier onset latency in the voluntary arm raise than in the sudden arm destabilization. No significant differences were observed in the muscle recruitment order for the sudden arm destabilization (p > 0.05). Conversely, for voluntary arm raise the MT, LT SA and anterior deltoid (AD) were activated significantly earlier than the UT (p < 0.001). Scapular muscles present a specific recruitment order during a predictable task: SA was activated prior to the AD and the UT after the AD, in a recruitment order of SA, AD, UT, MT, and LT. While in an unpredictable motor task, all muscles were activated after the destabilization without a specific recruitment order, but rather a simultaneous activation.     

Immediate effects and short-term retention of multi-modal instruction compared to written only on muscle activity during the prone horizontal abduction exercise in individuals with shoulder pain

In rehabilitation, exercise instructions are multi-modal and can include a focus of increasing mean activity of a target muscle and inhibiting aberrant synergistic muscle activity, particularly during shoulder exercises, such as the prone horizontal abduction (PHA). The objective was to compare the immediate effects and short-term retention of multi-modal exercise instruction by a physical therapist written only instruction on normalized mean upper and lower trapezius muscle activity during three phases (concentric/isometric/eccentric) versus of an isotonic PHA exercise between participants with and without shoulder pain. Surface electromyography (EMG) was recorded from fourteen healthy participants and twelve participants with shoulder pain during the PHA exercise under two conditions: (1) written only instructions and (2) multi-modal instruction. Retention of multi-modal instruction on muscle activity was assessed one week later. Results demonstrate 12.8–16.0% increase in lower trapezius muscle activity during the concentric and isometric phases with multi-modal instructions in both groups. Inhibition of the upper trapezius did not occur in either group. Facilitation effects were maintained in short-term follow-up. Findings suggest that regardless of shoulder pain, multi-modal instruction by a physical therapist facilitates greater neuromuscular activity of a targeted muscle compared to written instructions alone and these effects are retained.     

Effect of abducting and adducting muscle activity on glenohumeral translation, scapular kinematics and subacromial space width in vivo

It is currently unknown in which ways activity of the ab- and adductor shoulder muscles affects shoulder biomechanics (scapular kinematics and glenohumeral translation), and whether these changes are relevant for alterations of the subacromial space width. The objective of this experimental in vivo study was thus to test the hypotheses that potential changes of the subacromial space width (during antagonistic muscle activity) are caused by alterations of scapular kinematics and/or glenohumeral translation. The shoulders of 12 healthy subjects were investigated with an open MRI-system at 30 degrees, 60 degrees, 90 degrees, 120 degrees and 150 degrees of arm elevation. A force of 15N was applied to the distal humerus, once causing isometric contraction of the abductors and once contraction of the adductors. The scapulo-humeral rhythm, scapular tilting and glenohumeral translation were calculated from the MR image data for both abducting and adducting muscle activity. Adducting muscle activity led to significant increase of the subacromial space width in all arm positions. The scapulo-humeral rhythm (2.2-2.5) and scapular tilting (2-4 degrees) remained relatively constant during elevation, no significant difference was found between abducting and adducting muscle activity. The position of the humerus relative to the glenoid was, however, significantly (p < 0.05) different (inferior and anterior) for adducting versus abducting muscle activity in midrange elevation (60-120 degrees). These data show that the subacromial space can be effectively widened by adducting muscle activity, by affecting the position of the humerus relative to the glenoid. This effect may be employed for conservative treatment of the impingement syndrome.     

The effect of a novel gait retraining device on lower limb kinematics and muscle activation in healthy adults

The Re-Link Trainer (RLT) is a modified walking frame with a linkage system designed to apply a non-individualized kinematic constraint to normalize gait trajectory of the left limb. The premise behind the RLT is that a user’s lower limb is constrained into a physiologically normal gait pattern, ideally generating symmetry across gait cycle parameters and kinematics. This pilot study investigated adaptations in the natural gait pattern of healthy adults when using the RLT compared to normal overground walking. Bilateral lower limb kinematic and electromyography data were collected while participants walked overground at a self-selected speed, followed by walking in the RLT. A series of 2-way analyses of variance examined between-limb and between-condition differences. Peak hip extension and knee flexion were reduced bilaterally when walking in the RLT. Left peak hip extension occurred earlier in the gait cycle when using the RLT, but later for the right limb. Peak hip flexion was significantly increased and occurred earlier for the constrained limb, while peak plantarflexion was significantly reduced. Peak knee flexion and plantarflexion in the right limb occurred later when using the RLT. Significant bilateral reductions in peak electromyography amplitude were evident when walking in the RLT, along with a significant shift in when peak muscle activity was occurring. These findings suggest that the RLT does impose a significant constraint, but generates asymmetries in lower limb kinematics and muscle activity patterns. The large interindividual variation suggests users may utilize differing motor strategies to adapt their gait pattern to the imposed constraint.     

The influence of footwear on the electromyographic activity of selected lower limb muscles during walking

The purpose of this study was to compare the effects of a standard flexible shoe and a stability running shoe on lower limb muscle activity during walking. Twenty-eight young asymptomatic adults with flat-arched feet were recruited. While walking, electromyographic (EMG) activity was recorded from tibialis posterior and peroneus longus via intramuscular electrodes; and from tibialis anterior and medial gastrocnemius via surface electrodes. Three experimental conditions were assessed: (i) barefoot, (ii) a standard flexible shoe, (iii) a stability running shoe. Results showed significant differences for the peak amplitude and the time of peak amplitude for tibialis anterior, peroneus longus and medial gastrocnemius when comparing the three experimental conditions (p < 0.05). Significant differences were detected primarily between the barefoot and shoe conditions and with relatively small effect sizes for peroneus longus, tibialis anterior and medial gastrocnemius. Few significant differences were found between the two shoe styles. We discuss how these changes are most likely associated with the shoe upper bracing the foot, the shape of the shoe outer-sole and weight of the shoes. Further research is needed to investigate differences between these shoe styles when participants walk for longer distances (i.e. over 1000 m) and following fatigue.     

Kinematic models of the upper limb joints for multibody kinematics optimisation: An overview

Soft tissue artefact (STA), i.e. the motion of the skin, fat and muscles gliding on the underlying bone, may lead to a marker position error reaching up to 8.7 cm for the particular case of the scapula. Multibody kinematics optimisation (MKO) is one of the most efficient approaches used to reduce STA. It consists in minimising the distance between the positions of experimental markers on a subject skin and the simulated positions of the same markers embedded on a kinematic model. However, the efficiency of MKO directly relies on the chosen kinematic model. This paper proposes an overview of the different upper limb models available in the literature and a discussion about their applicability to MKO.The advantages of each joint model with respect to its biofidelity to functional anatomy are detailed both for the shoulder and the forearm areas. Models capabilities of personalisation and of adaptation to pathological cases are also discussed. Concerning model efficiency in terms of STA reduction in MKO algorithms, a lack of quantitative assessment in the literature is noted. In priority, future studies should concern the evaluation and quantification of STA reduction depending on upper limb joint constraints.