Shoulder rotator strength and torque steadiness in athletes with anterior shoulder instability or SLAP lesion

Does pain influence control of muscle force? A systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

In the presence of pain, whether clinical or experimentally induced, individuals commonly show impairments in the control of muscle force (commonly known as force steadiness). In this systematic review and meta-analysis, we synthesized the available evidence on the influence of clinical and experimental pain on force steadiness.

DATABASES AND DATA TREATMENT

MEDLINE, EMBASE, PubMed, CINAHL Plus and Web of Science databases were searched from their inception to 19 December 2023, using MeSH terms and pre-selected keywords related to pain and force steadiness. Two independent reviewers screened studies for inclusion and assessed their methodological quality using a modified Newcastle-Ottawa risk of bias tool.

RESULTS

In total, 32 studies (19 clinical pain and 13 experimental pain) were included. Meta-analyses revealed reduced force steadiness in the presence of clinical pain as measured by the coefficient of variation (CoV) and standard deviation (SD) of force (standardized mean difference; SMD = 0.80, 95% CI = 0.31-1.28 and SMD = 0.61, 95% CI = 0.11-1.11). These findings were supported by moderate and low strength of evidence respectively. In the presence of experimental pain, meta-analyses revealed reductions in force steadiness when measured by the CoV of force but not by the SD of force (SMD = 0.50, 95% CI = 0.01-0.99; and SMD = 0.44, 95% CI = -0.04 to 0.92), each supported by very low strength of evidence.

CONCLUSIONS

This work demonstrates that pain, particularly clinical pain, impairs force steadiness. Such impairments likely have clinical relevance and could become targets for treatment when managing people experiencing musculoskeletal pain.

SIGNIFICANCE STATEMENT

This systematic review and meta-analyses enhances our understanding of motor impairments observed in people experiencing musculoskeletal pain. It underscores the significance of incorporating force steadiness assessment when managing individuals experiencing musculoskeletal pain. Additionally, it suggests that future research should explore the potential benefits of force steadiness training in alleviating patients' symptoms and enhancing their functional performance. This could potentially lead to the development of innovative therapeutic approaches for individuals suffering from musculoskeletal pain.

Reliability of two devices for shoulder strength assessment: Wii Fit Balance Board and hand-held dynamometer

Background

The aim of this study was to compare the reliability and agreement between two devices - Wii Fit Balance Board (WBB) versus Hand-Held Dynamometer (HHD) to measure isometric strength during the athletic shoulder (ASH) test in healthy amateur rugby players.

Methods

Fifteen males (23.73 ± 2.8 years) completed two testing sessions. Maximal isometric contractions using the dominant arm (D) and non-dominant arm (ND) against a WBB and HHD were assessed at three angles of abduction (180°, 'I'; 135°, 'Y' and 90°, 'T'), in a prone lying position.

Results

The results indicate a very large correlation between the HHD and the WBB. WBB provides acceptable reliability at I-Test D (CV = 9.97%, ICC = 0.88) and HHD in the I-Test D (CV = 8.90%, ICC = 0.94), I-Test ND (CV = 8.60%, ICC = 0.95) in peak strength values. The HHD is most reliable in D ASH I-Y-T (CV = 10.94%) and WBB (CV = 11.05%). In the ND ASH I-Y-T test, the HHD is the most reliable (CV = 12.5%) compared to the WBB (CV = 14.43%).

Conclusions

These results suggest that WBB is a reliable device to assess strength in the ASH test with a very large correlation with the HHD. WBB and HHD are two affordable devices to assess isometric shoulder strength.

The impact of resistance-based training programs on throwing performance and throwing-related injuries in baseball players: A systematic review

The aim of this systematic review is to assess the effects of structured resistance training programs on the throwing performance and injury risk of baseball players, irrespective of their age or sex. The literature search was carried out on 18/10/2023, utilizing databases that include PubMed, Scopus, and the Web of Science. Our inclusion criteria encompassed research involving baseball players of all ages and sex who had undergone resistance-based training interventions. For comparison, we considered active control groups, irrespective of their exposure to additional training programs. The outcomes under investigation were related to throwing performance (i.e., throwing velocity and accuracy) and injuries associated with throwing. In our review, we exclusively included studies with a two- or multi-arm design. We evaluated the risk of bias using the PEDro scale. Out of the initial pool of 509 studies, we carefully examined 27 full-text articles and ultimately selected and analyzed 16 studies for inclusion in our review. Out of the 12 studies that compared and presented the inferential statistics for the post-training effects of the experimental versus control groups, it was observed that 8 of these studies demonstrated a significantly more favorable impact of the experimental group on enhancing throwing velocity when compared to the control group. Out of the three studies that compared the experimental and control groups in terms of throwing accuracy, only one study showed a significant improvement in the experimental group compared to the control group after the intervention. In conclusion, this systematic review indicates that resistance-based training interventions appear to be effective in enhancing throwing velocity. However, the evidence regarding the efficacy of these interventions in improving throwing accuracy is less robust. It is worth noting that while some experimental conditions may lead to an increase in injury rates, there is limited data available on this aspect, with only a few studies reporting on this variable.

Return to Sports Following Shoulder Injury: Clinical Evaluation, Isokinetic, and Functional Testing

ABSTRACT

The shoulder is commonly injured in overhead sports. This is associated with a high degree of mobility at the expense of stability, sports specific demands, high volume or intensity of practice and competition, biomechanical deficits, and poor technique. Following injury, the return to competition process includes nonsurgical or surgical treatment, comprehensive rehabilitation, and a structured return to sports program. The return to sports continuum is divided into phases which include return to practice of the sport, return to competition at a lower level or with reduced performance, and return to expected performance. Components of the return to sports decision include clinical evaluation of physical and psychological readiness, measurement of muscle strength using isokinetic tests, evaluation of overhead functional tasks, and progression in a supervised interval throwing program. The evidence for the effectiveness of return to sports programs following shoulder injury is limited but evolving and is an area that will merit continued investigation.

External to internal glenohumeral strength ratio in non-traumatic rotator cuff pathologies

Background and study aims

A correct agonist -antagonist strength relationship for shoulder external and internal rotation is necessary for functional stability of the shoulder. This strength relationship is described by the ratio of external to internal strength (ER/IR).The aim of this stydy is to produce comparative data as regards the ER/IR ratio in subjects with different non-traumatic rotator cuff diseases.

Design and setting

A cross-sectional study in an outpatient clinic in a tertiary care university hospital.

Methods

In 55 subjects with rotator cuff disease (confirmed by physical examination and assessed by ultrasound and magnetic resonance arthrography), the ER/IR ratio of the shoulder was isometrically measured with a hand-held dynamometer and compared with values pertaining to the unaffected shoulder of the same individuals.

Results

The mean ER/IR values in the overall group were 0.89 (SD 0.18) and 0.94 (SD 0.22) for the affected and unaffected shoulders, respectively. The ratio was 0.87 (SD 0.23) in patients with subdeltoid bursitis, 0.88 (SD 0.16) in rotator cuff tendinopathy and 0.87 (SD 0.22) in patients with rotator cuff tears.

Conclusions

The ER/IR ratio appears to be similar between the affected and unaffected shoulders of subjects with nontraumatic cuff pathologies.

Does the early phase of aging affect the morphology of biceps brachii and torque and total work of elbow flexors in healthy volunteers?

Upper and lower limbs can be affected by several diseases and changes related to current life habits, such as the sedentarism, technological advances, and even eating habits. This cross-sectional study investigated morphological adaptations of the biceps brachii muscle and the performance of the elbow flexors in healthy individuals in the early phase of aging. Thirty-two volunteers were separated according to age range (3rd, 4th, and 5th decades of life) and sex. Smaller diameters and subtypes of fibers were evaluated using muscle biopsies, and peak torque and total work were assessed using an isokinetic dynamometer. The variables were compared considering sex and decade, using mixed-effects linear models. The smaller diameter of all fiber types did not differ significantly between age groups for either sex. The proportion of oxidative fibers was reduced in male participants in the 4th (-20%) and 5th (-6%) decades of life compared to the 3rd decade, and there was an increase in the number of oxidative fibers in women from the 4th (+14%) to the 5th decade of life. There were no significant changes in the peak torque and total work between the analyzed age groups. The early phase of aging starts with alterations in the proportion of fibers, with a decrease in oxidative fibers in men and an increase in oxidative fibers in women. Smaller diameter, torque, and total work did not change over these decades of life.

Measuring complexity of muscle force control: Theoretical principles and clinical relevance in musculoskeletal research and practice

Musculoskeletal conditions affect bones, joints, and muscles of the locomotor system and are a leading cause of disability worldwide. This suggests that current musculoskeletal rehabilitation techniques fail to target the characteristics (e.g., physiological/physical/psychological) most influential for long-term musculoskeletal health. To identify whether a physiological characteristic is impaired, it must be measured. In neuromuscular control, traditional research approaches use magnitude-based measurements (e.g., peak force/standard deviation of force/coefficient of variation of force). However, magnitude-based measurements miss 'hidden information' regarding a physiological system's status across time. To better identify physiological characteristics that are clinically-important for long-term musculoskeletal health, other measurement approaches currently less applied in musculoskeletal research may be helpful. The purpose of this article is to present an introduction to technical and measurement principles for quantifying the 'complexity' of muscle force control as one representation of peripheral joint neuromuscular control. Complexity measurements are time-based and consider the irregular temporal structure of physiological signals. We review theoretical principles underlying measuring complexity of muscle force control and explain its clinical relevance for musculoskeletal scientists and clinicians. The principles include sensorimotor control of peripheral joints, muscle force signal construction and features, muscle force control measurement procedures, and variability and complexity variables. We propose the potential utility of measuring the complexity of muscle force control for diagnosing sensorimotor system impairment and prognosis following musculoskeletal disease or injury. This article will serve as an educational asset and a scientific resource that will inform future research directions to optimise rehabilitation for people with peripheral joint disease and injury.

Rotator cuff muscle imbalance associates with shoulder instability direction

BACKGROUND

Although muscle weakness and/or imbalance of the rotator cuff are thought to contribute to the development of shoulder instability, the association between muscular dysfunction and shoulder instability is not completely understood. The purpose of this study was to evaluate rotator cuff and deltoid muscle cross-sectional areas in different types of shoulder instability (anterior, posterior, and multidirectional instability [MDI]) and to determine the associations between muscular imbalance and shoulder instability direction.

METHODS

Preoperative magnetic resonance images of patients with shoulder instability who subsequently underwent arthroscopic glenohumeral labral repair or capsular plication were evaluated. Shoulder instability was classified into 3 categories by direction: (1) anterior, (2) posterior, and (3) MDI. The rotator cuff (supraspinatus, subscapularis, and infraspinatus + teres minor) and deltoid (anterior and posterior portions, and total) muscle areas were measured on T1 sagittal and axial slices, respectively. The ratios of the subscapularis to infraspinatus + teres minor area and the anterior deltoid to posterior deltoid area were calculated to quantify the transverse force couple imbalance.

RESULTS

A total of 189 patients were included, where each group consisted of 63 patients. The infraspinatus + teres minor muscle area was smaller than the subscapularis muscle area in the anterior instability group (P = .007). The subscapularis muscle area was smaller than the infraspinatus + teres minor muscle area in the posterior instability and MDI groups (P ≤ .003). The anterior deltoid muscle area was smaller than the posterior deltoid muscle area in all groups (P ≤ .001). The subscapularis-to-infraspinatus + teres minor area ratio in the anterior instability group (1.18 ± 0.40) was higher than that in the posterior instability and MDI groups (0.79 ± 0.31 and 0.93 ± 0.33, respectively; P < .001). There was no difference in the anterior deltoid-to-posterior deltoid area ratio among the 3 groups.

CONCLUSION

Patients with anterior instability have smaller muscle area of the posterior rotator cuff as compared with the anterior rotator cuff. In contrast, patients with posterior instability and MDI have smaller muscle area of the anterior rotator cuff as compared with the posterior rotator cuff. Thus, the direction of shoulder instability is associated with rotator cuff muscle area.

Alterations in peripheral joint muscle force control in adults with musculoskeletal disease, injury, surgery, or arthroplasty: A systematic review and meta-analysis

PURPOSE

To systematically review and analyse whether musculoskeletal conditions affect peripheral joint muscle force control (i.e. magnitude and/or complexity of force fluctuations).

METHODS

A literature search was conducted using MEDLINE, CINAHL and SPORTDiscus databases (from inception-8th April 2021) for studies involving: 1) participants with musculoskeletal disease, injury, surgery, or arthroplasty in the peripheral joints of the upper/lower limb; 2) comparison with an unaffected control group or unaffected contralateral limb; and 3) measures of the magnitude and/or complexity of force fluctuations during targeted isometric contractions. The methodological quality of studies was evaluated using a modified Downs and Black Quality Index. Studies were combined using the standardized mean difference (SMD) in a random-effects model.

RESULTS

14 studies (investigating 694 participants) were included in the meta-analysis. There was a significant effect of musculoskeletal conditions on peripheral joint muscle force coefficient of variation (CV; SMD = 0.19 [95 % CI 0.06, 0.32]), whereby individuals with musculoskeletal conditions exhibited greater CV than controls. Subgroup analyses revealed that CV was only greater: 1) when comparison was made between symptomatic and asymptomatic individuals (rather than between affected and contralateral limbs; SMD = 0.22 [95 % CI 0.07, 0.38]); 2) for conditions of the knee (SMD = 0.29 [95 % CI 0.14, 0.44]); and 3) for ACL injury post-surgery (SMD = 0.56 [95 % CI 0.36, 0.75]).

CONCLUSION

Musculoskeletal conditions result in an increase in peripheral joint muscle force CV, with this effect dependent on study design, peripheral joint, and surgical status. The greater force CV is indicative of decreased force steadiness and could have implications for long-term tissue health/day-to-day function.

Does grip strength correlate with rotator cuff strength in patients with atraumatic shoulder instability?

Aim

To investigate if there is a correlation between grip strength (GS) and rotator cuff (RC) strength in patients with atraumatic shoulder instability (ASI) and to compare the relationship between these two measures with that previously published for a healthy population. Moreover, to determine if testing GS could be incorporated as a surrogate clinical assessment for RC strength in these patients.

Methods

A total of 20 subjects with ASI were included. Out of the 20 patients, eight presented with bilateral instability, which constituted a total of 28 atraumatic unstable shoulders (N = 28). GS was measured using a Jamar hand-dynamometer. External rotation (ER) and internal rotation (IR) strength was tested in inner and outer ranges using a hand-held dynamometer (HHD). Pearson’s correlation test was computed to investigate the relationship. Multiple linear regression was conducted to predict GS based on RC strength.

Results

Significant and strong positive correlations were found between GS and inner-range IR (r = 0.764, P < 0.001), inner-range ER (r = 0.611, P = 0.001), outer-range IR (r = 0.817, P < 0.001), and outer-range ER (r = 0.736, P < 0.001). A significant regression equation was found (F (4, 23) = 13.254, P < 0.001), with an R2 of 0.697 indicating that RC strength explained 69.7% of the variance in GS.

Conclusions

The results support the hypothesis showing that GS is strongly associated with RC strength in ASI patients. The simplicity of handgrip testing allows it to be used in clinical scenarios where sophisticated assessment tools are not available. GS is a convenient means to monitor patient progress during shoulder rehabilitation programs.

Submaximal Elastic Resistance Band Tests to Estimate Upper and Lower Extremity Maximal Muscle Strength

Muscle strength assessment is fundamental to track the progress of performance and prescribe correct exercise intensity. In field settings, simple tests are preferred. This study develops equations to estimate maximal muscle strength in upper- and lower-extremity muscles based on submaximal elastic resistance tests. Healthy adults (n = 26) performed a maximal test (1 RM) to validate the ability of the subsequent submaximal tests to determine maximal muscle strength, with elastic bands. Using a within-group repeated measures design, three submaximal tests of 40%, 60%, and 80% during (1) shoulder abduction, (2) shoulder external rotation, (3) hip adduction, and (4) prone knee flexion were performed. The association between number of repetitions and relative intensity was modeled with both 1st and 2nd order polynomials to determine the best predictive validity. For both upper-extremity tests, a strong linear association between repetitions and relative intensity was found (R² = 0.97–1.00). By contrast, for the lower-extremity tests, the associations were fitted better with a 2nd order polynomial (R² = 1.00). The results from the present study provide formulas for predicting maximal muscles strength based on submaximal resistance in four different muscles groups and show a muscle-group-specific association between repetitions and intensity.

The validity of the sphygmomanometer for shoulder strength assessment in amateur rugby union players

OBJECTIVES

To determine the concurrent validity of a sphygmomanometer for assessing shoulder strength in the I, Y and T positions during the athletic shoulder test (ASH test). Force platforms were used as the gold standard measurement tool for this purpose.

DESIGN

Shoulder strength was assessed using force platforms and a sphygmomanometer, both placed on the floor and the participant positioned prone. One rater assessed strength, taking three measurements in each of the I, Y and T positions, using the sphygmomanometer and force platforms. Concurrent validity was calculated using the force platforms as the gold standard device.

SETTING

Data was collected within the treatment room of an amateur rugby club.

PARTICIPANTS

Twenty male amateur rugby players (25.15 years old ± 3.27 years) were recruited for this study.

MAIN OUTCOME MEASURES

Peak force across the shoulder girdle was assessed using the force platforms and sphygmomanometer which provided values in Newtons (N) and millimetres of mercury (mmHg) respectively.

RESULTS

Results showed high concurrent validity (Pearsons r = 0.76-0.81) between the sphygmomanometer and the force platform. Coefficient of determination (r² = 0.59-0.67) showed the sphygmomanometer to have a valid predictive model in the I, Y and T positions.

CONCLUSIONS

The sphygmomanometer is suitable for monitoring force transfer across the shoulder during the ASH test, and is able to quantify peak force in mmHg. The sphygmomanometer enables coaches and clinicians to accurately quantify force production across the shoulder girdle in order to screen and monitor players at a low cost.

Time to peak torque and acceleration time are altered in male patients following traumatic shoulder instability

BACKGROUND

Numerous authors have evaluated the strength of the rotator cuff muscles in patients with shoulder instability. However, only limited data are available with regard to neuromuscular control in patients with traumatic anterior shoulder instability, in particular at 90° of abduction. This study was designed to assess muscle strength and neuromuscular control ability using time to peak torque and acceleration time in nonathletic patients with traumatic anterior shoulder instability.

METHODS

Isokinetic muscle performance testing was performed in 20 male nonathletic anterior shoulder instability patients compared with 20 side-matched asymptomatic volunteers. Isokinetic muscle performance testing was performed at an angular velocity of 180°/s with 90° of shoulder abduction. Muscle strength and neuromuscular control (time to peak torque and acceleration time) of the internal rotators (IRs) and external rotators (ERs) were measured.

RESULTS

There were no significant differences in muscle strength of the IRs and ERs between the 2 groups. The injured shoulder showed delayed neuromuscular control in both the IRs and ERs in the instability patients compared with the normal control subjects (time to peak torque, P = .023 for IRs and P = .020 for ERs; acceleration time, P = .035 for IRs and P = .021 for ERs).

CONCLUSION

The neuromuscular control of both the IRs and ERs was decreased in male nonathletic patients with traumatic anterior shoulder instability even though muscle strength was not altered. Therefore, clinicians and therapists should implement exercises that aim to restore neuromuscular control in the rehabilitation of nonathletic patients with anterior shoulder instability.

Scapular muscles weakness in subjects with traumatic anterior glenohumeral instability

OBJECTIVE

To investigate possible alterations on scapular muscle strength in subjects with traumatic anterior glenohumeral instability.

DESIGN

Cross-sectional study.

SETTING

Laboratory setting.

PARTICIPANTS

Fifty-two subjects of both sexes: 26 healthy and 26 with traumatic anterior glenohumeral instability.

MAIN OUTCOME MEASURES

Subjects performed maximal isometric and concentric isokinetic contractions of shoulder protraction and retraction in scapular and sagittal planes, at slow (12.2 cm/s) and fast (36.6 cm/s) speeds.

RESULTS

Subjects with glenohumeral instability presented lower peak force of protraction and retraction during isometric and fast speed tests in the scapular plane; and of isometric protraction in the sagittal plane.

CONCLUSIONS

People with traumatic anterior glenohumeral instability present muscle weakness of scapular protractors and retractors. Considering the importance of the scapulothoracic muscles for the dynamic stability of the glenohumeral joint, strengthening of these muscles is recommended for rehabilitation of traumatic anterior glenohumeral instability.

Torque steadiness and muscle activation are bilaterally impaired during shoulder abduction and flexion in chronic post-stroke subjects

OBJECTIVE

To characterize sensorimotor control and muscle activation in the shoulder of chronic hemiparetic during abduction and flexion in maximal and submaximal isometric contractions. Furthermore, to correlate submaximal sensorimotor control with motor impairment and degree of shoulder subluxation.

METHODS

Thirteen chronic hemiparetic post-stroke age-gender matched with healthy were included. Isometric torques were assessed using a dynamometer. Electromyographic activity of the anterior and middle deltoid, upper trapezius, pectoralis major and serratus anterior muscles were collected. Variables were calculated for torque: peak, time to target, standard deviation (SD), coefficient of variation (CV), and standard error (RMSE); for muscle activity: maximum and minimum values, range and coefficient of activation. Motor impairment was determined by Fugl-Meyer and shoulder subluxation was measured with a caliper.

RESULTS

Paretic and non-paretic limbs reduced peak and muscle activation during maximal isometric contraction. Paretic limb generated lower force when compared with non-paretic and control. Paretic and non-paretic presented higher values of SD, CV, RMSE, and CV for prime mover muscles and minimum values for all muscles during steadiness. No correlation was found between sensorimotor control, motor impairment and shoulder subluxation.

CONCLUSION

Chronic hemiparetic presented bilateral deficits in sensorimotor and muscle control during maximal and submaximal shoulder abduction and flexion.

Quantitative analysis of peak torque and power-velocity characteristics of shoulder rotator muscles after arthroscopic labral repair

OBJECTIVES

We aimed to use biomechanical testing to assess differences in the power and strength of patients who participated in a short-term, home-based rehabilitation program following arthroscopic labral repair compared with a healthy control group.

DESIGN

The functional outcomes of patients who underwent arthroscopic labral repair followed by self-directed short-term rehabilitation at home were compared with age- and body mass index (BMI)-matched healthy controls.

METHODS

Group I included 20 male patients who had undergone arthroscopic labral repair after being diagnosed with recurrent anterior glenohumeral joint instability without bony lesions of the humeral head or glenoid. Postoperatively, they participated in physical therapy for 17±4 appointments, followed by self-guided home-based exercises. Group II included 25 males without injuries. The two groups were matched for age and BMI. The orthopaedic examination, functional tests, and biomechanical measurements were performed under isokinetic conditions at an average of 16±3 months postoperatively.

RESULTS

Significant differences were observed in range of shoulder rotation on the operative shoulder compared with the unaffected side and in the dominant arms of the control group. The patients were also found to have significant deficits in biomechanical parameters such as power and peak torque angle.

CONCLUSIONS

Significant deficits in peak torque, power, and peak torque angle during external and internal shoulder rotation remained up to 16 months after arthroscopic labral repair. Further research is needed to understand the changes in shoulder power assessment after labral repair.