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The role of scapular dyskinesis as a risk factor of shoulder injury has been largely discussed. However, most studies have focused on symptomatic patients and less is known on the asymptomatic dyskinetic scapula. Removing the confounding effects of the pathologies could contribute to better characterize the scapula dyskinesis. As muscle properties (strength, fatigue, nerve injury …) have been identified as causative factors of scapular dyskinesis, this study focuses specifically on characterizing the protractor and retractor muscles of the dyskinetic scapula. Thirteen asymptomatic dyskinetic volunteers were compared to eleven asymptomatic non-dyskinetic control volunteers. Muscle characteristics were evaluated in terms of maximal strength, fatigue resistance and electromyographic activity during a functional closed-chained task. The results did not identify kinematic or muscle activity significant differences between the dyskinetic and the control group even in fatigue conditions. However, the results demonstrated that protractors vs. retractors fatigue resistance ratios were imbalanced (<0.8) in the dyskinetic group and significantly lower than in the non-dyskinetic one. Our study suggests that that strength imbalances are not necessarily related to the presence of pain at the shoulder joint. These results demonstrated the importance to complete the clinical assessments of the scapula with strength evaluations even for asymptomatic sport practitioners., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Context: Scapular dyskinesis is a shoulder dysfunction that can be asymptomatic or associated with pain or weakness. Reduced strength and fatigue resistance of the scapular protractor and retractor muscles that stabilize the scapula might contribute to dyskinesis., Objectives: To determine the strength and fatigue resistance profiles of participants with symptomatic or asymptomatic scapular dyskinesis and compare them with healthy control (HC) individuals using isokinetic assessment., Design: Cross-sectional study., Setting: University hospital., Patients or Other Participants: Twenty HC individuals and 21 overhead athletes with symptomatic (n = 10) or asymptomatic (n = 11) scapular dyskinesis., Main Outcome Measure(s): Strength (peak torque, maximum work), fatigue resistance (total work), and protraction:retraction ratios measured during a closed chain isokinetic protocol (40 repetitions in concentric mode at 24.4 cm/s)., Results: The scapular protractors' strength and fatigue resistance were higher (P < .01) in HC individuals (peak torque = 5.0 ± 0.9 N/kg, maximum work = 2.4 ± 0.5 J/kg, total work = 72.4 ± 0.6 J/kg) than in asymptomatic (peak torque = 3.4 ± 0.7 N/kg, maximum work = 1.7 ± 0.4 J/kg, total work = 50.0 ± 13.7 J/kg) or symptomatic (peak torque = 3.8 ± 0.6 N/kg, maximum work = 1.8 ± 0.3 J/kg, total work = 58.1 ± 12.9 J/kg) dyskinetic participants. The symptomatic dyskinetic group presented the highest retractor strength and fatigue resistance (P < .01) values (peak torque = 5.2 ± 0.6 N/kg, maximum work = 2.9 ± 0.8 J/kg, total work = 87.7 ± 22.7 J/kg), followed by the HC individuals (peak torque = 4.7 ± 1.0 N/kg, maximum work = 2.1 ± 0.5 J/kg, total work = 65.3 ± 17.9 J/kg) and the asymptomatic dyskinetic participants (peak torque = 3.9 ± 1.0 N/kg, maximum work = 1.9 ± 0.6 J/kg, total work = 58.6 ± 18.5 J/kg). The protraction:retraction ratios showed a gradual decrease (P < .001) from the HC individuals (1.1) to the asymptomatic (0.9) and symptomatic (0.7) dyskinetic participants., Conclusions: Scapular dyskinesis is characterized by weaker scapular protractors and reduced agonist:antagonist ratios, especially when patients are symptomatic. Targeting the scapular protractors to achieve a better balance of scapular musculature in rehabilitation and strengthening programs may improve shoulder symptoms and function, but more interventional studies are required., (© by the National Athletic Trainers’ Association, Inc.)

Purpose: The main goal of this prospective study was to identify the most significant intrinsic risk factors for shoulder pain by measuring strength developed by shoulder rotators and by carrying out various morphostatic assessments., Methods: Sixty-six players (mean ± SD age = 24 ± 5 yr) were recruited from nine volleyball teams from the first and second divisions (34 men and 32 women) to participate in the study. Before the start of the volleyball season, all the participants completed a preseason questionnaire and underwent both a bilateral isokinetic evaluation of the shoulders and morphostatic measurements. During the subsequent 6 months of the competition period, the players reported through a weekly questionnaire any shoulder pain experienced., Results: During the ongoing season, 23% (15 of 66 players) of the volleyball players experienced dominant shoulder pain. Interestingly, participants who reported a history of dominant shoulder pain were found to have nine times higher risk of suffering further pain in their dominant shoulder. The eccentric maximal strength developed by the internal and external rotators was found to represent a protective factor in the volleyball players (respective odds ratios = 0.946, P = 0.01 and 0.94, P = 0.05). No risk factors were found among the shoulder morphostatic measurements., Conclusion: In our study, the evaluation of shoulder rotator muscle strength through isokinetic assessment, especially eccentric mode, appeared to be the most contributing parameter to identify risk factors for shoulder pain. This evaluation should allow to better identify players at risk.

Isokinetic assessment of the shoulder rotator cuff is a common component of shoulder muscles assessment. Nevertheless, the extensive mobility of the shoulder poses great difficulty in finding a consensus protocol for evaluation. To select an optimal protocol, among three, based on the best reproducibility and reliability of strength scores derived from internal and external rotator tests. The dominant side external and internal rotator muscles of twelve healthy male subjects were evaluated based on a concentric protocol (60° s and 240° s) in three different test positions: two in lying supine with the arm in either 90° or 45° abduction and one in the seated position with the arm moving in the scapular plane on the dominant shoulder. Subjects were tested twice over 10 days. The two lying installations were associated with the lowest coefficient of variation (7·1-11·8%) and smallest detectable difference (7-15·9 N·m) for peak moment and strength ratios. Consequently, the lying positions were chosen for rotators assessment with 90° of abduction associated with a higher reproducibility for the agonist/antagonist ratios or 45° if some pain was provoked. In any case, the coefficient of variation did not exceed 12%. Based on a reproducibility and reliability analysis, we recommend the testing of isokinetic strength of the shoulder rotators to be conducted in supine lying, with the arm at 90° or 45° abduction in the frontal plane. [ABSTRACT FROM AUTHOR]

Background/Aims: Latissimus dorsi (LD) transfer in the case of breast reconstruction remains frequently used because this muscle provides a good size source of tissue in reconstructive surgery. Given that, the consequences of the LD removal on shoulder function and the actual loss of maximal strength developed must be investigated. Methods: Twenty women (50 ± 7·5 years old) were evaluated before surgery, 3 and 6 months after an unilateral transfer of a pedicle flap of LD muscle used for breast reconstruction. Women performed a bilateral shoulder isokinetic assessment [for the internal rotators (IRs) and external rotators and for the abductor and adductor (ADD) muscles] allowing the establishment of bilateral muscular deficit status and the study of agonist/antagonist muscle ratios. The algofunctional and clinical status of the shoulders was analysed by the means of Constant score and specific shoulder clinical tests. The women did not perform any specific strengthening of muscle shoulder after surgery. Results: The isokinetic assessment showed a muscle weakness 3 and 6 months after LD transfer, mainly on the ADDs (33 ± 9% at 6 months) and on the IRs (16 ± 11% at 6 months). The Constant score significantly decreased after surgery on the operated shoulder. Women with a Constant score impairment showed pain during specific shoulder clinical tests. We also found a correlation between Constant score impairment and internal rotators weakness or rotator muscle imbalance. Conclusion: Given those results, we could advocate a specific shoulder strengthening after LD transfer, focused mainly on the IRs and ADDs. [ABSTRACT FROM AUTHOR]

Objective. To establish the inter-session reproducibility of isokinetic concentric strength and fatigue profile of the elbow flexors and extensors in sedentary women. Methods. Forty healthy women who were physically inactive or engaged in recreational sports were included in the study. Strength was evaluated at 60 and 180°/s. The fatigue protocol consisted of 30 maximal-intensity elbow flexion and extension at 180°/s. Results. The extensors were stronger than flexors while no dominance effect was apparent. In addition the work output of the extensors during the fatigue protocol was larger than the flexors', the previous being more fatigue resistant. A dominance effect was observed for the extensors in the fatiguing protocol. Reproducibility expressed by the coefficient of variation was less or equal to 11%. Conclusions. This study highlights satisfactory reproducibility of isokinetic strength and fatigue parameters. The values derived may be useful for interpretation of clinical tests or characterization of pathological states in women with similar characteristics. [ABSTRACT FROM AUTHOR]

The article establishes possible relationships between isokinetic muscle strength of the shoulder, physical features and field performances such as spike velocity in volleyball. The study of the tests for volleyball players is described. It was found that spike velocity is correlated with the strength performance of the dominant shoulder in all concentric mode conditions. The results could provide useful information for training management.

Objective Isokinetic tests regularly contribute to the assessment of muscle performance. However, to evaluate an athlete who mainly uses the lactic anaerobic metabolism to perform or in specific pathological contexts, fatigue-resistance protocol could be complementary to short maximal strength evaluation. Although the reproducibility of the protocol has been demonstrated by Bosquet et al. [1] (2010), what about the reproductibility of the measured parameters and various “fatigue index” proposed by dynamometers and used in the clinic and in the literature? Material and method Seventeen subjects, moderately active, performed 30 reciprocal maximal concentric contractions on three occasions with one 7–10 days recovery between each session. The peak torque (PT) and the maximal work (MW) of each repetition computed and subsequently use to compile eleven measured parameters and build forty-four index. The reproducibility of each parameter and index was evaluated through their ICC (2,1), SEM and respective MD. Results The ICC values of the measured parameters for the knee extensors are almost always higher than 0.8 while those for flexor range between 0.7 and 0.8. The ICC values for built “fatigue index” are less than 0.7 and 0.5 respectively for the extensors and flexors. No significant difference was observed between the reproducibility of PT and that of MW (whether for the extensors or flexors or for the measured parameters and “fatigue index”). Discussion In view of the values obtained in our population, it appears that no “fatigue index”or calculated quotient (quotient of the last x repetitions by the first x or accumulated repetitions by the best…) seems sufficiently reproducible for clinical or scientific use! Only the measured parameters such as the best repetition, total or partial sum have a (very) high or excellent reproducibility and can therefore be used in clinical or research domain. [ABSTRACT FROM AUTHOR]

Concentric and eccentric contractions are allowed by the use of isokinetic dynamometers. Testing in the eccentric mode seems relevant for some muscle groups involved in a protective decelerating action through specific gestures. After hamstring injury, the eccentric isokinetic assessment highlights occasional deficits whereas the concentric performance is already normalized. A mixed Hamstring eccentric/quadriceps concentric ratio seems more functional and was shown to be more discriminant as factor predicting further hamstring injury. Prevention and return to play criteria after injury should regularly include eccentric isokinetic testing in specific sports activities. Due to their role in overhead activities, the rotator muscle groups of the shoulder could also require eccentric testing. Practicing upper limb sports entails frequently the reduction of a mixed external rotators eccentric/internal rotators concentric. Recently, a prospective study identified the eccentric strength deficit of external rotators and internal rotators as a risk factor for shoulder injury in volleyball. In rehabilitation, sub-maximal eccentric contractions are recommended for treating some musculo-tendinous injuries. Such programs aim at improving the tendon properties (tendinopathy) as well as healing process after muscle injury. The isokinetic dynamometer allows controlling very precisely the key parameters, which are contraction intensity, speed and range of motion. [ABSTRACT FROM AUTHOR]