Normative values of agonist-antagonist shoulder strength ratios of adults aged 20 to 78 years

Older age is associated with decreased overall shoulder strength but not direction-specific differences in the three-dimensional feasible torque space

Shoulder strength is reduced in older adults but has only been assessed in planar motions that do not reflect the diverse requirements of daily tasks. We quantified the impact of age on strength spanning the three degrees of freedom relevant to shoulder function, referred to as the feasible torque space. We hypothesized that the feasible torque space would differ with age and expected this age-effect to reflect direction-specific deficits. We measured strength in 32 directions to characterize the feasible torque space of the shoulder in participants without shoulder pain or tendinous pathology (n = 39, 19-86 years). We modeled the feasible torque space for each participant as an ellipsoid, computed the ellipsoid size and direction-specific metrics (ellipsoid position, orientation, and shape), and then tested the effect of age on each metric. Age was negatively associated with ellipsoid size (a measure of overall strength magnitude; -0.0033 ± 0.0007 (Nm/kg)/year, p < 0.0001). Contrary to our expectation, the effect of age on the direction-specific metrics did not reach statistical significance. The effect of age did not differ significantly between male and female participants. Three-dimensional strength measurements allowed us to constrain the direction of participants' maximum torque production and characterize the entire feasible torque space. Our findings support a generalized shoulder strengthening program to address age-related shoulder weakness in those without pain or pathology. Clinical exam findings of imbalanced weakness may suggest underlying pathology beyond an effect of age. Longitudinal studies are needed to determine the positive or negative impact of our results.

Reliability of Dynamic Shoulder Strength Test Battery Using Multi-Joint Isokinetic Device

This study aimed to determine the absolute and relative reliability of concentric and eccentric flexion, extension, horizontal abduction, and adduction movements of the shoulder using a functional electromechanical dynamometer (FEMD). Forty-three active male university students (23.51 ± 4.72 years) were examined for concentric and eccentric strength of shoulder flexion, extension, horizontal abduction, and horizontal adduction with an isokinetic test at 0.80 m·s-1. Relative reliability was determined by intraclass correlation coefficients (ICCs) with 95% confidence intervals. Absolute reliability was quantified by the standard error of measurement (SEM) and coefficient of variation (CV). Reliability was very high to extremely high for all movements on concentric and eccentric strength measurements (ICC: 0.76-0.94, SEM: 0.63-6.57%, CV: 9.40-19.63%). The results of this study provide compelling evidence for the absolute and relative reliability of concentric and eccentric flexion, extension, horizontal abduction, and horizontal adduction shoulder isokinetic strength tests in asymptomatic adults. The mean concentric force was the most reliable strength value for all tests.

A Systematic Review of Isokinetic Muscle Strength in a Healthy Population With Special Reference to Age and Gender

CONTEXT

Despite increasing use of reference values in isokinetic measurements and increasing importance, there is no systematic review of the reference values for lower and upper limb isokinetic muscle strength.

OBJECTIVE

A systematic review to analyze studies on the reference values and protocols for the measurement for upper and lower limb isokinetic muscle strength in an untrained and noninjured healthy population.

DATA SOURCES

MEDLINE, Scopus, Scielo, and CINAHL (from the earliest date available to June 2020).

STUDY SELECTION

Studies that measured a set of reference values for isokinetic muscle strength.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 3.

DATA EXTRACTION

Two reviewers selected studies independently. Data related to participants characteristics, outcomes of interest, isokinetic parameters, reference values for isokinetic muscle strength, and quality of evidence assessment were systematically reviewed independently by 2 authors.

RESULTS

A total of 31 studies met the study criteria. The included studies were used to synthesize the isokinetic muscle strength data according to age-group and sex. We extracted 1845 normative data related to isokinetic strength. Of these, 1181 items referred to lower limbs and 664 items to upper limbs.

CONCLUSION

In general, agonist muscle groups are stronger than antagonist muscles, and the men tend to obtain higher strength values than women. The angular velocity varied from 10 to 300 deg/s. The reference values identified can be useful for professionals to obtain during the isokinetic evaluation of the diagnostic parameters of muscle deficiency.

Experimentally quantifying the feasible torque space of the human shoulder

Daily tasks rely on our ability to generate multi-dimensional shoulder torques. When function is limited, strength assessments are used to identify impairments and guide treatment. However, these assessments are often one-dimensional and limited in their sensitivity to diagnose shoulder pathology. To address these limitations, we have proposed novel metrics to quantify shoulder torque capacity in all directions. To quantify the feasible torque space of the shoulder, we measured maximal volitional shoulder torques in 32 unique directions and fit an ellipsoid model to these data. This ellipsoid model was used to quantify overall strength magnitude, strength balance, and the directions in which participants were strongest and weakest. We used these metrics to characterize three-dimensional shoulder strength in healthy adults and demonstrated their repeatability across days. Finally, using musculoskeletal simulations, we showed that our proposed metrics can distinguish between changes in muscle strength associated with aging or rotator cuff tears and quantified the influence of altered experimental conditions on this diagnostic capacity. Our results demonstrate that the proposed metrics can robustly quantify the feasible torque space of the shoulder and may provide a clinically useful description of the functional capacity of the shoulder in health and disease.

Differences in Shoulder Internal Rotation Strength Between Baseball Players With Ulnar Collateral Ligament Reconstruction and Healthy Controls

Background:

Studies have indicated decreased shoulder internal rotation (IR) and external rotation (ER) strength in the throwing limb of baseball players after ulnar collateral ligament injury. There is limited evidence on the recovery of shoulder rotation strength after primary ulnar collateral ligament reconstruction (UCLR).

Hypothesis:

At the time of return to throwing, baseball players who underwent UCLR would demonstrate decreased IR and ER shoulder strength in the throwing arm as compared with healthy baseball players.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Male competitive high school and collegiate baseball athletes participated in this study. Athletes who underwent UCLR were compared with healthy controls who were matched by age, height, weight, and position. Bilateral isometric shoulder ER and IR strength was measured using a handheld dynamometer for all participants at the time of initial evaluation (UCLR group) and throughout the course of a season (healthy group). Independent t tests were run to calculate mean differences in ER and IR shoulder strength between the groups, with significance set at P < .05.

Results:

A total of 86 baseball athletes participated in this study (43 UCLR group, 43 healthy group). At the time of return to throwing (mean ± SD, 194 ± 30 days postoperatively), the 2 groups demonstrated no significant differences in nonthrowing arm ER or IR strength (P = .143 and .994, respectively). No significant difference was found between groups for throwing arm ER strength (P = .921); however, the UCLR group demonstrated significantly less throwing arm IR strength than the healthy group (144.2 ± 27.8 vs 157.6 ± 27.1 N; P = .023).

Conclusion:

The results of this study demonstrate that throwing arm rotator cuff strength may not fully recover before the initiation of a return-to-throwing program after UCLR. These data provide a potential framework for clinicians to assist in the management and exercise prescription of the baseball athlete after UCLR and before medical release and the initiation of a return-to-throwing program.

A comparison of isokinetic rotator cuff performance in wheelchair basketball athletes vs. non-athletes with spinal cord injury

OBJECTIVES

This study aimed to compare the isokinetic peak torque and, secondarily, other parameters of the rotator cuff in the shoulders of paraplegic wheelchair basketball athletes and non-athletes controls.

DESIGN

Cross-sectional study.

METHODS

Thirty-six complete spinal cord injured individuals aged between 18 and 45 years performed an isokinetic evaluation of peak torque, power, and work exerted by the rotator cuff muscle group, in a Biodex System. All Concentric isokinetic tests were performed in the seated position with the shoulder at a 45° abduction from the scapular plane and flexed at 30° to the frontal plane. Subjects completed five repetitions at 60°/s and 180°/s, and ten repetitions at 300°/s, bilaterally, with an interval of one minute between each series. Statistical analysis (t-test, P < 0.05) compared athletes and non-athletes, dominant and non-dominant upper limbs according to all isokinetic parameters and angular velocities.

RESULTS

Peak torque/weight, work, and muscle power of wheelchair basketball athletes were significantly greater than those of the control group (P < 0.05), but there were no statistical differences between dominant and non-dominant upper limb. Internal rotators were stronger than the external rotators both for athletes and for non-athletes. There is a positive correlation between peak torque and time since injury.

CONCLUSIONS

Wheelchair basketball athletes showed greater peak torque and other muscle performance parameters, which suggest that wheelchair basketball influences the shoulder musculature of those with traumatic spinal cord injury.

Isokinetic strength of shoulder rotator muscles in powerlifters: correlation between isometric and concentric muscle actions

BACKGROUND

Isokinetic strength has been useful to assess muscle function related to sports and prevent injuries. The present study measured the isokinetic isometric and concentric shoulder rotators strength, agonist/antagonist ratio, and examined the relationships between isometric and concentric peak torque, and agonist/antagonist ratio in powerlifters compared to a control group.

METHODS

The participants were divided into two groups: powerlifters group (n=14) and physically active group (n=9). Participants' were evaluated on isokinetic dynamometer for isometric, and concentric (two velocities, 60°/s and 180°/s) strength of shoulder external (ER) internal rotation (IR). Isometric contractions lasted 10 seconds, and concentric modes were 5 repetitions.

RESULTS

Bilateral significant differences, between dominant and non-dominant side, were found in ER peak torque at isometric mode in powerlifters group (p=0.021). Powerlifters showed higher IR peak torque at isometric mode in dominant (p=0.040) and non-dominant side (p=0.014) than physically active group. Pearson correlations between isometric peak torque and concentric velocities ranged between 0.49 and 0.89 for powerlifters group, and between 0.73 and 0.93 for physically active group. For agonist/antagonist ratio, pearson correlation ranged between 0.47 and 0.83 for powerlifters group, and between 0.48 and 0.86 for physically active group.

CONCLUSIONS

The bilateral differences in ER movement at isometric mode in powerlifters suggest that exercises for shoulder rotators must be included on training for joint safety and balance between sides despite isometric shoulder rotators strength in powerlifters was higher than physically active individuals. Results presented positive correlation between both muscle actions, isometric and concentric, in peak torque and agonist/antagonist ratio.

Muscle strength and inflammatory response to the training load in rowers

Background

Regular exercise leads to changes in muscle metabolism. The consequence of this is the adaptation to higher training loads.The aim of this study was to evaluate biomechanical and biochemical parameters describing the functions of skeletal muscles in periods when changes in training forms were introduced.

Methods

Seventeen male sweep-oar rowers, members of the Polish national rowing team, participated. The study was carried out at the beginning and at the end of the preparatory period. In the first and second examination measurements of torques of selected muscle groups and blood biochemical analysis were performed.

Results

There was observed a statistically significant decrease in the relative global force of the right lower limb between both terms of examination. A statistically significant increase in maximum torque was found for torso flexors. In the case of muscles responsible for torso rotation, a statistically significant decrease in the torque values of right torso rotators was observed. A significant difference was found with respect to creatine kinase activity, total testosterone concentration, total testosterone to cortisol ratio and total phenolics concentration (p < 0.05).

Conclusion

The study shows that the rowers’ training should be more focused on building the strength of lower limbs to prevent the overload of lumbar spine and that the amount of force developed may be significantly affected by the antioxidant potential of rowers.

Reference values for muscle strength: a systematic review with a descriptive meta-analysis

BACKGROUND

Muscle strength is an important component of health.

OBJECTIVE

To describe and evaluate the studies which have established the reference values for muscle strength on healthy individuals and to synthesize these values with a descriptive meta-analysis approach.

METHODS

A systematic review was performed in MEDLINE, LILACS, and SciELO databases. Studies that investigated the reference values for muscle strength of two or more appendicular/axial muscle groups of health individuals were included. Methodological quality, including risk of bias was assessed by the QUADAS-2. Data extracted included: country of the study, sample size, population characteristics, equipment/method used, and muscle groups evaluated.

RESULTS

Of the 414 studies identified, 46 were included. Most of the studies had adequate methodological quality. Included studies evaluated: appendicular (80.4%) and axial (36.9%) muscles; adults (78.3%), elderly (58.7%), adolescents (43.5%), children (23.9%); isometric (91.3%) and isokinetic (17.4%) strength. Six studies (13%) with similar procedures were synthesized with meta-analysis. Generally, the coefficient of variation values that resulted from the meta-analysis ranged from 20.1% to 30% and were similar to those reported by the original studies. The meta-analysis synthesized the reference values of isometric strength of 14 muscle groups of the dominant/non-dominant sides of the upper/lower limbs of adults/elderly from developed countries, using dynamometers/myometer.

CONCLUSIONS

Most of the included studies had adequate methodological quality. The meta-analysis provided reference values for the isometric strength of 14 appendicular muscle groups of the dominant/non-dominant sides, measured with dynamometers/myometers, of men/women, of adults/elderly. These data may be used to interpret the results of the evaluations and establish appropriate treatment goals.

Significantly Increased Odds of Reporting Previous Shoulder Injuries in Female Marines Based on Larger Magnitude Shoulder Rotator Bilateral Strength Differences

Background:

Musculoskeletal injuries to the extremities are a primary concern for the United States (US) military. One possible injury risk factor in this population is side-to-side strength imbalance.

Purpose:

To examine the odds of reporting a previous shoulder injury in US Marine Corps Ground Combat Element Integrated Task Force volunteers based on side-to-side strength differences in isokinetic shoulder strength.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Male (n = 219) and female (n = 91) Marines were included in this analysis. Peak torque values from 5 shoulder internal/external rotation repetitions were averaged and normalized to body weight. The difference in side-to-side strength measurements was calculated as the absolute value of the limb difference divided by the mean peak torque of the dominant limb. Participants were placed into groups based on the magnitude of these differences: <10%, 10% to 20%, and >20%. Odds ratios (ORs) and 95% CIs were calculated.

Results:

When separated by sex, 13.2% of men reported an injury, while 5.5% of women reported an injury. Female Marines with >20% internal rotation side-to-side strength differences demonstrated increased odds of reporting a previous shoulder injury compared with female Marines with <10% strength differences (OR, 15.4; 95% CI, 1.4-167.2; P = .03 ) and female Marines with 10% to 20% strength differences (OR, 13.9; 95% CI, 1.3-151.2; P = .04). No significant ORs were demonstrated in male Marines.

Conclusion:

Marines with larger magnitude internal rotation strength differences demonstrated increased odds of reporting a previous shoulder injury compared with those with lesser magnitude differences. Additionally, female sex appears to drastically affect the increased odds of reporting shoulder injuries (OR, 13.9-15.4) with larger magnitude differences (ie, >20%) compared with those with lesser magnitude differences (ie, <10% and 10%-20%). The retrospective cohort design of this study cannot delineate cause and effect but establishes a relationship between female Marines and greater odds of larger magnitude strength differences after returning from an injury.

Characteristics of upper extremity's muscle strength in Turkish national wheelchair basketball players team

The objective of this study was to reveal characteristics of muscle strength of upper extremities of wheelchair (WC) basketball players and to ensure more-specific training program preparation. Isokinetic muscle strength of 12 WC basketball players were assessed by ISOMED 2000 device. The assessment protocol was evaluated at 60°/sec velocity with 5 times repeated force and at 240°/sec with 15 times repeated force. This protocol was carried out individually for shoulder flexion-extension and wrist flexion-extension movements at the right and left extremities. The flexion/extension ratio was determined to be outside of the ratios accepted as normal for primarily shoulder joint and for wrist joint. The extension movement was stronger than flexion movement in the shoulders at both velocities and the flexion movement was stronger than ex-tension movement in the wrist. The repeat times where the peak torque occurred were 2–3 repeats at 60°/sec velocity during flexion and extension movements for the wrist and shoulders, and the peak torque occurred at an average of 5–6 repeats in the shoulders at 240°/sec velocity and it occurred at 3–4 repeats in the wrist. The angles where the peak torque of the shoulder flexion and extension occurred varied between 80°–115° at both velocities, and it varied between 5°–30° angles for the wrist. As this study revealed, determination of muscle strength characteristics of WC athletes and especially using objective isokinetic devices will guide the planning of the appropriate training and exercise programs and preventing sports injuries in long term.

Eccentric and isometric shoulder rotator cuff strength testing using a hand-held dynamometer: reference values for overhead athletes

PURPOSE

In order to provide science-based guidelines for injury prevention or return to play, regular measurement of isometric and eccentric internal (IR) and external (ER) rotator strength is warranted in overhead athletes. However, up to date, no normative database exists regarding these values, when measured with a hand-held dynamometer. Therefore, the purpose of the study was to provide a normative database on isometric and eccentric rotator cuff (RC) strength values in a sample of overhead athletes, and to discuss gender, age and sports differences.

METHODS

A HHD was used to measure RC strength in 201 overhead athletes between 18 and 50 years old from three different sports disciplines: tennis, volleyball and handball. Isometric as well as eccentric strength was measured in different shoulder positions. Outcome variables of interest were isometric ER and IR strength, eccentric ER strength, and intermuscular strength ratios ER/IR.

RESULTS

Our results show significant side, gender and sports discipline differences in the isometric and eccentric RC strength. However, when normalized to body weight, gender differences often are absent. In general, strength differences are in favour of the dominant side, the male athletes and handball. Intermuscular ER/IR ratios showed gender, sports, and side differences.

CONCLUSION

This normative database is necessary to help the clinician in the evaluation of RC strength in healthy and injured overhead athletes. In view of the preventive screening and return-to-play decisions in overhead athletes, normalization to body weight and calculating intermuscular ratios are key points in this evaluation.

LEVEL OF EVIDENCE

Diagnostic study, Level III.

Analysis of effects of loading and postural demands on upper limb reaching in older adults using statistical parametric mapping

Continuous time-series data are frequently distilled into single values and analyzed using discrete statistical methods, underutilizing large datasets. Statistical parametric mapping (SPM) allows hypotheses over the entire spectrum, but consistency with discrete analyses of kinematic data is unclear. We applied SPM to evaluate effect of load and postural demands during reaching on thoracohumeral kinematics in older and young adults, and examined consistency between one-dimensional SPM and discrete analyses of the same dataset. We hypothesized that older adults would choose postures that bring the humerus anterior to the frontal plane (towards flexion) even for low demand tasks, and that SPM would reveal differences persisting over larger temporal portions of the reach. Ten healthy older (72.4±3.1yrs) and 16 young (22.9±2.5yrs) adults reached upward and forward with high and low loads. SPM and discrete t-tests were used to analyze group effects for elevation plane, elevation, and axial rotation joint angles and velocity. Older adults used more positive (anterior) elevation plane and less elevated postures to initiate and terminate reaching (p<0.008), with long duration differences during termination. When reaching upward, differences in elevation persisted over longer temporal periods at midreach for high loads (32-58% of reach) compared to low load (41-45%). SPM and discrete analyses were consistent, but SPM permitted clear identification of temporal periods over which differences persisted, while discrete methods allowed analysis of extracted values, like ROM. This work highlights the utility of SPM to analyze kinematics time series data, and emphasizes importance of task selection when assessing age-related changes in movement.

Functional and radiographic outcomes of nonoperative treatment of displaced adolescent clavicle fractures

BACKGROUND

Studies of adult patients suggest that nonoperative treatment of clavicle fractures may result in functional disability, but this has not been demonstrated in adolescents. The purpose of this study was to determine the functional outcomes after nonoperative treatment of displaced, shortened, midshaft clavicle fractures in adolescents.

METHODS

Adolescents ten to eighteen years of age with an isolated, completely displaced, shortened, midshaft clavicle fracture sustained between 2009 and 2011 were recruited for this study. Injury and final radiographs were assessed for displacement, shortening, and clavicle length. Maximal and endurance strength testing was performed with the Baltimore Therapeutic Equipment (BTE) machine, with use of the uninjured shoulder as an internal control. Shoulder range of motion and clavicle length were assessed clinically, and patient-oriented outcomes were obtained.

RESULTS

Sixteen patients (four of whom were female) with an average age (and standard deviation) of 14.2 ± 2 years and a mean duration of follow-up of 2 ± 1 years were included in the study. Fifteen patients were right-hand dominant and one was ambidextrous, and thirteen of the fractures occurred in the nondominant limb. Compared with the uninjured limb, no differences were noted in range of motion or strength except for an 8% decrease in maximal shoulder external rotation strength (p = 0.04) and a 11% loss of shoulder abduction endurance strength (p = 0.04). Radiographs demonstrated a 100% union rate but significant shortening compared with the uninjured clavicle (p ≤ 0.001). SANE (Single Assessment Numeric Evaluation), QuickDASH (shortened version of the Disabilities of the Arm, Shoulder and Hand questionnaire), and Constant scores were similar between sides. Fifteen of the sixteen patients were satisfied with the appearance of the clavicle, and all returned to full activity, including the preinjury (or a higher) level of sports participation.

CONCLUSIONS

Regardless of patient age, sports participation, and final clavicle shortening, no differences in pain, strength, shoulder range of motion, or subjective outcome scores were found between the injured and uninjured limbs of adolescents treated nonoperatively for a displaced, shortened, midshaft clavicle fracture.

Shoulder rotational profiles in young healthy elite female and male badminton players

The aim of the present study was to profile shoulder passive range of motion (ROM) and isometric strength for external (ER) and internal (IR) rotation as part of a preseason screening in adolescent national badminton players. Passive external range of motion (EROM) and internal range of motion (IROM) were examined on the dominant and nondominant shoulder in 31 adolescent national badminton players (12 females and 19 males) with a standard goniometer. Muscle strength was examined with a hand-held dynamometer in ER and IR. Total range of motion (TROM = EROM+IROM) was lower on the dominant side compared with the nondominant side in both groups (P < 0.001). Males were generally stronger than females in all strength measurements except for IR on the dominant side (P < 0.01). In females, IR dominant side strength was greater compared with IR on the nondominant side (P < 0.05). TROM was reduced on the dominant side compared with the nondominant side in young elite badminton players, irrespective of gender. No rotational strength differences existed between the dominant and nondominant side in male players, but in female players a higher IR strength on the dominant side was not balanced by a higher ER strength.

The role of intrinsic factors in control of arm movement direction: implications from directional preferences

The role of extrinsic and intrinsic factors in control of arm movement direction remains under debate. We addressed this question by investigating preferences in selection of movement direction and whether factors causing these preferences have extrinsic or intrinsic nature. An unconstrained free-stroke drawing task was used during which participants produced straight strokes on a horizontal table, choosing the direction and the beginning and end of each stroke arbitrarily. The variation of the initial arm postures across strokes provided a possibility to distinguish between the extrinsic and intrinsic origins of directional biases. Although participants were encouraged to produce strokes equally in all directions, each participant demonstrated preferences for some directions over the others. However, the preferred directions were not consistent across participants, suggesting no directional preferences in extrinsic space. Consistent biases toward certain directions were revealed in intrinsic space representing initial arm postures. Factors contributing to the revealed preferences were analyzed within the optimal control framework. The major bias was explained by a tendency predicted by the leading joint hypothesis (LJH) to minimize active interference with interaction torque generated by shoulder motion at the elbow. Some minor biases may represent movements of minimal inertial resistance or maximal kinematic manipulability. These results support a crucial role of intrinsic factors in control of the movement direction of the arm. Based on the LJH interpretation of the major bias, we hypothesize that the dominant tendency was to minimize neural effort for control of arm intersegmental dynamics. Possible organization of neural processes underlying optimal selection of movement direction is discussed.

Hand-held dynamometer testing of the internal and external rotator musculature based on selected positions to establish normative data and unilateral ratios

HYPOTHESIS

Objective documentation is needed of shoulder internal and external rotator strength using hand-held dynamometry in selected positions commonly used in a clinic. We compared strength measures and unilateral ratios between gender, limbs (dominant, nondominant), and 3 testing positions. We hypothesized that men would be stronger than women, the dominant shoulder would be stronger than the nondominant shoulder, and the seated neutral (0° adduction) and seated 30° abduction, 30° scaption, 30° diagonal (30°-30°-30°) positions would be stronger than the prone at 90°-90° position.

MATERIALS AND METHODS

Three positions (prone at 90°, seated at neutral, and seated at 30°-30°-30°) were evaluated in 181 individuals using hand-held dynamometry. Three separate 3-factor (limb by position by gender) analyses of variance were conducted on internal rotation, external rotation, and unilateral ratios.

RESULTS

Although the dominant limb was significantly stronger (P < .001) than the nondominant for internal rotation, there was no difference for external rotation. The external rotators demonstrated significantly greater strength in the prone at 90° position compared with the seated at neutral (P = .001) and seated at 30°-30°-30° (P = .002) positions. The internal rotators demonstrated significantly greater (P = .036) strength in the neutral position than in the prone at 90° position for the women. The unilateral ratio of external rotators/internal rotators ranged from 86% to 99%. For the women, the prone at 90° ratio was significantly greater than seated at neutral (P = .001) and seated at 30°-30°-30° (P = .001) positions. Moderate strength relationships (r = 0.506 to 0.572) were revealed between body mass and all strength measures.

DISCUSSION

The results of this study provide evidence to interpret normative data, bilateral comparisons and unilateral ratios of the internal/external rotators in the 3 selected positions.

CONCLUSION

Because there are no differences between the seated at neutral and 30°-30°-30° positions and the advantages it offers, we recommend the 30°-30°-30° position for testing and the initiation of rehabilitation.

Avaliação muscular isocinética da articulação do ombro em atletas da Seleção Brasileira de voleibol sub-19 e sub-21 masculino

INTRODUÇÃO E OBJETIVO: A musculatura do complexo do ombro possui um papel importante na produção de força e potência articular no voleibol, permitindo a realização do gesto esportivo de maneira coordenada. A documentação objetiva produzida pela avaliação isocinética auxilia no diagnóstico e na prevenção de lesões do complexo do ombro, além de ser uma ferramenta útil no prognóstico do retorno rápido e seguro para a prática esportiva do atleta lesionado. O objetivo deste estudo foi avaliar o desempenho muscular isocinético dos músculos rotadores laterais e mediais da articulação glenoumeral em atletas de voleibol da Seleção Brasileira Masculina sub-19 e sub-21. MÉTODOS: O protocolo realizado durante o teste foi de cinco repetições máximas de rotação lateral e medial de ombro no modo concêntrico-concêntrico na velocidade de 60º/s e 30 repetições na velocidade de 360º/s. Análise de variância (ANOVA) mista foi utilizada para avaliar as variáveis dependentes: trabalho máximo e torque máximo normalizados pela massa corporal dos músculos rotadores laterais e mediais do ombro, razão agonista/antagonista nas duas velocidades e índice de fadiga muscular. RESULTADOS: A análise dos dados demonstrou haver um desequilíbrio entre os rotadores laterais e mediais (razão agonista/antagonista) da articulação do ombro em atletas brasileiros de voleibol da categoria sub-21, revelando menor força relativa dos rotadores laterais. CONCLUSÃO: Foi possível identificar alterações em atletas de voleibol que, associadas a demandas específicas do esporte, podem levar à sintomatologia no complexo do ombro e/ou queda da performance.

The reliability of hand-held dynamometry in measuring isometric strength of the shoulder internal and external rotator musculature using a stabilization device

Although hand-held dynamometry is considered an objective method of measuring strength, the reliability of the procedure can be compromised by inadequate tester strength and insufficient stabilization of the dynamometer and subject. The purpose of this study was to investigate the test-retest reliability of a hand-held dynamometer with the use of a portable stabilization device while testing the shoulder internal and external rotator musculature. The isometric strength of the shoulder rotator musculature was tested twice in 30 asymptomatic adult volunteers (15 male and 15 female) between 18 and 63 years of age by using an intrasession design. Consistency of the testing protocol was maintained through the use of an arm stabilization apparatus, which fixed the arm in 30 degrees of the scapular plane and a portable dynamometer stabilization device. Intraclass correlation coefficients (ICC's) were high, ranging from ICC (3,1) = 0.971-0.972 for the test-retest trials of internal and external rotation. There was no significant difference between sessions one and two for maximum internal rotation (p = 0.431) and maximum external rotation strength (p = 0.780). The results indicate that the testing protocol with stabilization device is a reliable method for measuring strength of the internal and external rotator shoulder musculature.

Morphology of deltoid origin and end tendons--a generic model

This study provides a model of the complex deltoid origin and end tendons, as a basis for further anatomical, biomechanical and clinical research. Although the deltoid is used in transpositions with upper limb paralysis, its detailed morphology and segmentation has not been object of much study. Morphologically, the deltoid faces two distinct challenges. It closely envelops a ball joint, and it reduces its width over a short distance from a very wide origin along clavicle, acromion and spina scapula, to an insertion as narrow as the humerus. These challenges necessitate specific morphological tendon adaptations. A qualitative model for these tendons is developed by the stepwise transformation of a unipennate muscle model into a functional deltoid muscle. Each step is the solution to one of the mentioned morphological challenges. The final model is of an end tendon consisting of a continuous succession of bipennate end tendon blades centrally interspaced by unipennate tendon parts. The origin tendon consists of lamellae that interdigitate with the end tendon blades, creating a natural segmentation. The model is illustrated by qualitative dissection results. In addition, in view of a proliferation of terms found in the literature to describe deltoid tendons, tendon concepts are reviewed and the systematic use of the unique and simple terminology of 'origin and end tendons' is proposed.

Rotational strength, range of motion, and function in people with unaffected shoulders from various stages of life

Background

Different measurements are used to assess shoulder function, including range of motion, strength, functional performance and self-report function. To understand disablement, it is necessary to understand the relationship between impairments and function in persons without shoulder problems. This study was conducted to enhance existing comparative data in subjects without upper extremity pathology, and to assess the relationships between impairments (range of motion, strength) and self-reported or measured function/disability. The impact of age, gender and dominance was determined.

Methods

Two-hundred ninety-four subjects with unaffected shoulders were recruited. The subjects (mean age: 37 years old) were divided into three subgroups, 18–39, 40–59, and over 60 years of age. During a single session, at least two of the following variables were measured: self-reported function (shoulder disability scales), range of motion, isometric rotational strength, or upper limb functional performance (FIT-HaNSA). Two-way analysis of variance was used to determine, for each variable, the effects of age and gender. The relationship between the outcomes was established using Pearson product correlations.

Results

Men were significantly stronger than women for all age categories. There was an age-related decline in strength in men in the over-60 age category. Significant negative correlations between strength and range of motion were demonstrated (-0.22 <r < -0.32). Women had a significantly higher range of motion than men for external rotation in the 40–59 age category. Furthermore, the subjects in the over-60 age category experienced a decrease of range of motion. There was minimal disability reported in all age groups on self-report scales. Only the Simple Shoulder Test demonstrated significant decreases in the over-60 age category and correlated with age (r = -0.202).

Conclusion

Self-reported disability was low in individuals without upper extremity problems, although recruitment of such individuals was difficult in the older age groups due to the high prevalence of shoulder pathology. A low correlation between self-report disability and strength/range of motion in these unaffected subjects reflects the lack of disability reported by all subjects without pathology despite normal variations in strength and motion.

An integer programming model for optimizing shoulder rehabilitation

Strength restoration is one goal of shoulder rehabilitation following rotator cuff repair surgery. However, the time spent in a physical rehabilitation setting is limited. The objective of this study was to develop a novel mathematical formulation for determining the optimal shoulder rehabilitation exercise protocol to restore normal shoulder strength given a time-constrained rehabilitation session. Strength gain was modeled using a linear dose-response function and biomechanical parameters of the shoulder musculature. Two different objective functions were tested: (1) one based on a least squares support vector machine using healthy and pathologic shoulder strengths (normative objective function), and (2) one which seeks to match the strength of the contralateral shoulder (contralateral objective function). The normative objective function was subject-independent and the optimal protocol consisted of four sets each of adduction and external rotation. The contralateral objective function was subject-specific and the typical optimal protocol consisted of various set combinations of abduction and internal and external rotation. These results are only partially consistent with current practice. Improvement of the current model is dependent on a better understanding of strength training adaptation and shoulder rehabilitation.

Effect of the Scapula Reposition Test on shoulder impingement symptoms and elevation strength in overhead athletes

STUDY DESIGN

Two group, repeated measures design.

OBJECTIVES

To determine whether manually repositioning the scapula using the Scapula Reposition Test (SRT) reduces pain and increases shoulder elevation strength in athletes with and without positive signs of shoulder impingement.

BACKGROUND

Symptom alteration tests may be useful in determining a subset of those with shoulder pathology who may benefit from interventions aimed at improving scapular motion abnormalities.

METHODS AND MEASURES

One hundred forty-two college athletes underwent testing for clinical signs of shoulder impingement. Tests provoking symptoms were repeated with the scapula manually repositioned into greater retraction and posterior tilt. A numeric rating scale was used to measure symptom intensity under both conditions. Isometric shoulder elevation strength was measured using a mounted dynamometer with the scapula in its natural position and with manual repositioning. A paired t test was used to compare the strength between positions. The frequency of a significant increase in strength with scapular repositioning, defined as the minimal detectable change (90% confidence interval), was also assessed.

RESULTS

Of the 98 athletes with a positive impingement test, 46 had reduced pain with scapular repositioning. Although repositioning produced an increase in strength in both the impingement (P=.001) and non-impingement groups (P=.012), a significant increase in strength was found with repositioning in only 26% of athletes with, and 29% of athletes without positive signs for shoulder impingement.

CONCLUSION

The SRT is a simple clinical test that may potentially be useful in an impairment based classification approach to shoulder problems.

Interfering effects of the task demands of grip force and mental processing on isometric shoulder strength and muscle activity

The purpose of this study was to examine the interfering effects of physical and mental tasks on shoulder isometric strength in different postures. Fifteen volunteers (seven women, eight men) performed a series of isometric shoulder exertions at 30 degrees , 60 degrees and 90 degrees of both shoulder flexion and abduction alone and with the addition of a 30% grip force, a mental task (Stroop test) and both additional tasks simultaneously. The shoulder tasks were completed either at maximal intensity, or while maintaining a shoulder posture without any additional effort. Surface electromyography (EMG) from seven muscles of the shoulder girdle and shoulder moment were collected for each 6 s shoulder exertion. When normalized to maximum exertion, no differences were found between genders and no differences existed between conditions when subjects maintained each posture without exerted force. In the maximal shoulder exertion trials, an increase in shoulder angle (in either plane) resulted in an increase in EMG in most muscles, while shoulder moment decreased in flexion and remained constant in abduction. Shoulder moments and muscle activation were greatest in the shoulder exertion alone condition followed by adding a 30% grip and the Stroop test, with the addition of both tasks further reducing the exerted shoulder moment and EMG. However, muscle activity did not always decrease with shoulder strength and remained elevated, indicating a complex coactivation pattern produced by an interfering role of the tasks. Overall, it was found that a mental task can have the same or greater effect as a concurrent grip and should be considered when assessing muscular loading in the workplace, as typical biomechanical modelling may underestimate internal loads. The results not only provide valuable shoulder strength data but also practical strength values, depending on additional tasks.

Upper-extremity torque production in men with paraplegia who use wheelchairs

OBJECTIVES

To study maximal upper-extremity torque values and agonist/antagonist torque ratios in a sample of individuals with paraplegia and to compare these values with a sample of age-, gender-, and weight-matched able-bodied individuals.

DESIGN

Cross-sectional, case-control study.

SETTING

A biomechanics laboratory.

PARTICIPANTS

A convenience sample of 15 men with complete (American Spinal Injury Association class A) T5-L2 paraplegia and 15 able-bodied control subjects.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Maximal isometric torques of 12 upper-extremity muscle groups (shoulder, elbow, and wrist flexion and extension; shoulder abduction and adduction; shoulder internal and external rotation; elbow pronation and supination) were measured with custom dynamometers.

RESULTS

Maximal torque values and agonist/antagonist torque ratios for the shoulder, elbow, and wrist functions did not differ between the control subjects and those with complete paraplegia, with the exception of the supination/pronation torque ratio, which was significantly higher in the able-bodied control group.

CONCLUSION

Wheelchair propulsion and other functional activities, such as transfers, do not significantly affect maximum torque production of the upper extremities in individuals with paraplegia. On the basis of these findings, arguments that upper-extremity muscle imbalances are important contributory factors to upper-extremity pain and dysfunction in this group may be too simplistic.