Isokinetic muscle strength parameters for shoulder movements

Sex differences in strength at the shoulder: a systematic review

Background

Understanding differential strength capability between sexes is critical in ergonomics and task design. Variations in study designs and outcome measures generates challenges in establishing workplace guidelines for strength requirements to minimize upper extremity risk for workers. The purpose of this systematic review was to collate and summarize sex differences in strength at the shoulder across movement directions and contraction types.

Methods

A total of 3,294 articles were screened from four databases (Embase, Medline, SCOPUS, and Web of Science). Eligibility criteria included observational studies, direct measurement of muscular joint, and healthy adult participants (18-65 years old). Strength outcome measures were normalized to percentages of male outputs to allow comparisons across articles.

Results

A total of 63 studies were included within the final review. Majority of articles observed increased strength in males; the gap between male-female strength was greater in flexion and internal/external rotation, with females generating ~30% of male strength; scaption strength ratios were most consistent of the movement groups, with females generating 55-62% of male strength.

Conclusion

Sex strength differences should be considered as an important factor for workplace task design as women are more at risk for occupational-related injuries than men in equivalent strength requirements. Differences in strength were not synonymous across motions; females demonstrated increased disparity relative to male strength in horizontal flexion/extension, forward flexion and internal/external rotation. Some movements had an extremely limited pool of available studies for examination which identified critical research gaps within the literature. Collating and quantifying strength differences is critical for effective workstation design with a range of users to mitigate potential overexertion risk and musculoskeletal injury.

A Systematic Review and Meta-analysis of Functional Shoulder Impairment After Latissimus Dorsi Breast Reconstruction

PURPOSE

The latissimus dorsi flap (LDF) is a very reliable flap and may be used for a multitude of reconstructive purposes. It is widely used for breast reconstruction when performed. It has few complications, except for a possible impact on shoulder function. The aims of this study were to evaluate the validity of the literature by investigating the level of evidence and to perform a meta-analysis.

METHODS

A systematic literature search was conducted using the databases PubMed, Scopus, and Web of Science. Predictor variables were shoulder function after breast reconstruction with the LDF. Articles were chosen according to 4 different outcomes: shoulder range of motion (ROM), shoulder strength, DASH score, and subjective evaluation.

RESULTS

Twenty-six articles were found, including 1045 patients: 8 level II, 16 level III, 1 level IV, and 1 level V articles. The meta-analysis showed that both ROMs for flexion and abduction are significantly impaired at less than or at 3 months of follow-up.

CONCLUSIONS

There are several influencing factors, such as age, smoking, obesity, radiotherapy, and physiotherapy. Moreover, the impact on shoulder function seemed influenced by the type of thoracodorsal vessel-based flap. From the level of evidence analysis, there is a tendency that the LDF transfer does affect shoulder function. This limitation seems to be minimal, and few patients experience a major impact on shoulder function. However, the existing literature on total shoulder impairment after breast reconstruction with LDF is insufficient to draw any final conclusion. There is a need for future studies and current articles that suggest that the initial measurement should be performed preoperatively (preferably at the time of diagnosis or initial biopsy) and follow-ups with measurements at 6, 12, and 24 months (long-term effect) after surgery. We recommend measurements of both operated and nonoperated sides. Each measurement should be accompanied by a history with special emphasis on shoulder function. The methods of measuring outcomes of recommendation are DASH score, ROM with use of a goniometer preferably by a physiotherapist or a health care professional trained by a physiotherapist, and strength measured by, for example, a handheld dynamometer.

Dynamic and static shoulder strength relationship and predictive model

Static strength is typically used to standardize occupational tasks in an effort to limit over-exertion injuries; however, workplace tasks are commonly dynamic in nature. The purpose of this investigation was to assess factors influencing isokinetic shoulder strength and to develop predictive equations for isokinetic shoulder flexion and extension strength using isometric strength. Fifteen women performed a set of concentric isokinetic and isometric shoulder flexion and extension maximal exertions across a series of movement planes, angular velocities, and grip types. Data were used to generate two stepwise multiple regression models for predicting isokinetic shoulder flexion and exertion strength across the various exertion parameters. The final regression models explained a high degree of variance in predicting isokinetic shoulder flexion (R² = 0.59) and extension (R² = 0.67) with a subset of four and five inputs, respectively. The predictive equations can help establish acceptable force limits for workplace tasks requiring dynamic actions using more easily attainable static forces.

Effects of hand grip exercise on shoulder joint internal rotation and external rotation peak torque

BACKGROUND AND OBJECTIVES

The goal of this study is to analyze the effects of hand grip training on shoulder joint internal rotation (IR)/external rotation (ER) peak torque for healthy people.

METHODS

The research was conducted on 23 healthy adults in their 20 s-30 s who volunteered to participate in the experiment. Hand grip power test was performed on both hands of the research subjects before/after the test to study changes in hand grip power. Isokinetic machine was used to measure the concentric IRPT (internal rotation peak torque) and concentric ERPT (external rotation peak torque) at the velocity of 60°/sec, 90°/sec, and 180°/sec before/after the test. Hand grip training was performed daily on the subject's right hand only for four weeks according to exercise program. Finally, hand grip power of both hands and the maximum torque values of shoulder joint IR/ER were measured before/after the test and analyzed.

RESULTS

There was a statistically significant difference in the hand grip power of the right hand, which was subject to hand grip training, after the experiment. Also, statistically significant difference for shoulder ERPT was found at 60°/sec.

CONCLUSION

Hand grip training has a positive effect on shoulder joint IRPT/ERPT and therefore can help strengthen muscles around the shoulder without using weight on the shoulder. Consequently, hand grip training would help maintain strengthen the muscles around the shoulder in the early phase of rehabilitation process after shoulder surgery.

Functional torque ratios and torque curve analysis of shoulder rotations in overhead athletes with and without impingement symptoms

In this study, we evaluated the peak torque, functional torque ratios, and torque curve profile of the shoulder rotators in overhead athletes with impingement symptoms so as to examine possible alterations in response to sports training and shoulder pain. Twenty-one overhead athletes with impingement symptoms were compared with 25 overhead athletes and 21 non-athletes, none of whom were symptomatic for impingement. The participants performed five maximal isokinetic concentric and eccentric contractions of medial and lateral shoulder rotations at 1.57 rad · s(-1) and 3.14 rad · s(-1). Isokinetic peak torque was used to calculate the eccentric lateral rotation-to-concentric medial rotation and the eccentric medial rotation-to-concentric lateral rotation ratios. An analysis of the torque curve profiles was also carried out. The eccentric lateral rotation-to-concentric medial rotation torque ratio of asymptomatic athletes was lower than that of non-athletes at both test velocities. The concentric medial rotation isokinetic peak torque of the asymptomatic athletes, at 3.14 rad · s(-1), was greater than that of the non-athletes, and the peak appeared to occur earlier in the movement for athletes than non-athletes. These findings suggest that there may be adaptations to shoulder function in response to throwing practice. The eccentric medial rotation-to-concentric lateral rotation torque ratio was altered neither by the practice of university-level overhead sports nor impingement symptoms.

Strength Values of Shoulder Internal and External Rotators in Elite Volleyball Players

Objective:

To determine concentric shoulder external-internal rotator strength, dominant and non-dominant shoulder differences and agonist/antagonist ratios.

Design:

A transversal study of isokinetic dynamometry of healthy shoulders, 95% confidence intervals are presented.

Participants:

35 asymptomatic elite, male volleyball players.

Measurements:

Peak torque normalized for body weight was recorded at 60, 180, and 300°/sec. with a Cybex 6000 dynamometer.

Results:

(1) internal rotators were significantly stronger than external rotators of the same shoulder; (2) internal rotators of the dominant arm were significantly stronger than of the non-dominant arm; (3) no difference existed between external rotators of the dominant and the non-dominant arm; (4) external–internal rotator ratios of the dominant arm were significantly lower than of the non-dominant arm; and (5) no differences were found between the ratios of each arm separately.

Conclusions:

Data presented are important for interpreting isokinetic shoulder rotator strength tests in elite volleyball players and could be relevant in rehabilitation and prevention of shoulder injuries.

Effects of velocity on upper to lower extremity muscular work and power output ratios of intercollegiate athletes

OBJECTIVES

Peak torque expresses a point output which may, but does not always, correlate well with full range output measures such as work or power, particularly in a rehabilitating muscle. This study evaluates isokinetic performance variables, particularly (a) flexor to extensor work and power output ratios of upper and lower extremities and (b) overall upper to lower extremity work and power ratios, in intercollegiate athletes. The purpose was to ascertain how speeds of 30 and 180 degrees/s influence agonist to antagonist ratios for torque, work, and power and to determine the effects of these speeds on upper to lower limb flexor (F), extensor (E), and combined (F + E) ratios, as a guide to rehabilitation protocols and outcomes after injury.

METHODS

Twenty seven athletic men without upper or lower extremity clinical histories were tested isokinetically at slow and moderately fast speeds likely to be encountered in early stages of rehabilitation after injury. Seated knee extensor and flexor outputs, particularly work and power, were investigated, as were full range elbow extensor and flexor outputs. The subjects were morphologically similar in linearity and muscularity (coefficient of variation 4.17%) so that standardisation of isokinetic outputs to body mass effectively normalised for strength differences due to body size. Peak torque (N.m/kg), total work (J/kg), and average power (W/kg) for elbow and knee flexions and extensions were measured on a Cybex 6000 isokinetic dynamometer. With respect to the raw data, the four test conditions (F at 30 degrees/s; E at 30 degrees/s; F at 180 degrees/s; E at 180 degrees/s) were analysed by one way analysis of variance. Reciprocal (agonist to antagonist) F to E ratios of the upper and lower extremities were calculated, as were upper to lower extremity flexor, extensor, and combined (F + E) ratios. Speed related differences between the derived ratios were analysed by Student's t tests (related samples).

RESULTS

At the speeds tested all torque responses exhibited velocity related decrements at rates that kept flexor to extensor ratios and upper to lower extremity ratios constant (p > 0.05) for work and power. All upper extremity relative torque, work, and power flexion responses were equal to extension responses (p > 0.05) regardless of speed. Conversely, all lower extremity relative measures of torque, work, and power of flexors were significantly lower than extensor responses. In the case of both upper and lower extremities, work and power F to E ratios were unaffected by speed. Moreover, increasing speed from 30 to 180 degrees/s had no effect on upper to lower extremity work and power ratios, whether for flexion, extension, or flexion and extension combined.

CONCLUSIONS

Peak torque responses may not adequately reflect tension development through an extensive range of motion. Total work produced and mean power generated, on the other hand, are highly relevant measures of performance, and these, expressed as F to E ratios, are unaffected by speeds of 30 and 180 degrees/s, whether for upper or lower extremities or for upper to lower extremities. In this sample, regardless of speed, the upper extremity produced 55% of the work and 39% of the power of the lower extremity, when flexor and extensor outputs were combined. Injured athletes are, in the early stages of function restoration, often not able to exert tension at fast speeds. An understanding of upper to lower extremity muscular work and power ratios has important implications for muscle strengthening after injury. Knowledge of normal upper to lower extremity work and power output ratios at slow to moderately fast isokinetic speeds is particularly useful in cases of bilateral upper (or lower) extremity rehabilitation, when the performance of a contralateral limb cannot be used as a yardstick.

The effect of age, speed, and arm dominance on shoulder function in untrained men

Bilateral shoulder motor output measurements were obtained in 40 subjects with a Biodex dynamometer. The subjects included two groups, a younger group (20 to 30 years) and an older group (50 to 60 years). They were engaged in low to moderate levels of occupational and spare-time physical activity. Each subject performed three maximum effort shoulder movements in flexion/extension, abduction/adduction, and internal/external rotation at 60 degrees/sec and 120 degrees/sec. Side tested, axis, and speed were randomly selected. The findings indicate that a significant decline occurred in peak torque, work, and power for all axes of movement at both speeds when the older group was compared with the younger group. A decline in peak torque and work and a corresponding increase in power resulting from an increase in speed occurred in both age groups. The effect of age was the same at 60 degrees/sec and at 120 degrees/sec. Overall, no difference in dominant and nondominant motor function was seen in either the younger or older untrained men.

Isokinetic strength relationships in shoulder muscles

The purpose of this study was to extend and refine former findings which related to strength characteristics of the major muscle groups operating on the glenohumeral joint. Based on preliminary isokinetic evaluation of five women and five men, which indicated that overall dominance was not associated with significantly stronger muscles, the dominant shoulders of 30 normal non-athletic subjects, 15 women and 15 men, were tested concentrically and eccentrically, at 60, 120 and 180 degrees /s. The descending order of muscle strength at both contraction modes and for both genders was: extensors, adductors, flexors, abductors, internal rotators and external rotators. Inter-muscle groups' strength correlation coefficients have indicated significant, moderate-fairly strong, relationships in men but not in women. The implications of these findings in terms of testing and shoulder muscle conditioning are discussed. RELEVANCE:--Analysis and interpretation of shoulder muscle dysfunction, and implementation of conditioning protocols, require the availability of normative values pertaining to the common modes of contraction and relative to an acceptable and velocity setup. This study provides a representative data base of normal subjects which may serve for these purposes.

Dynamic shoulder flexion strength: for use in occupational risk analysis and clinical assessment

Given the likelihood of increased risk of musculoskeletal injury when joint torque strength demands approach the maximum isometric torque, this study determined the flexion torque strength capabilities of the shoulder in young men and women. To our knowledge this is the first study to report dynamic shoulder flexion torques. Peak static flexion torque values were collected at shoulder angles of 0° (anatomical position) and 45° of flexion in 25 female and 26 male subjects seated in an upright position. Dynamic concentric and eccentric shoulder flexion torques were collected at 50° s(-1) angular velocity from 0° to each subject's comfortable flexion limit on a KIN-COM dynamometer. Results indicated that for both static and dynamic strength measures, female subjects produced, on average, half of the torque output of males. Mean male flexion torques were: static at 0° = 89.9 N m; static at 45° = 68.6 N m; dynamic at 45° = 46.9 N m (concentric); dynamic at 45° = 75.3 N m (eccentric).

Shoulder pain in wheelchair athletes. The role of muscle imbalance

Shoulder rotator cuff impingement syndrome is a common and disabling problem for the wheelchair athlete. In this study we investigated the role of shoulder strength imbalance as a factor for the development of this syndrome. Nineteen paraplegic male athletes underwent clinical and isokinetic examination of both shoulders with peak torque values measured in abduction, adduction, and internal and external rotation. Twenty athletic, able-bodied men without shoulder problems were tested as controls. Ten (26%) of the paraplegic athletes had rotator cuff impingement syndrome. The results of the isokinetic testing demonstrated that 1) the paraplegics' shoulders were stronger than the controls in all directions (P < 0.05); 2) the strength ratio of abduction: adduction was higher for paraplegic athletes (P < 0.05); 3) paraplegics' shoulders with rotator cuff impingement syndrome were weaker in adduction and external and internal rotation than the paraplegic athletes without impingement syndrome (P < 0.05); and 4) paraplegics' shoulders with rotator cuff impingement syndrome had higher abduction:adduction and abduction:internal rotation strength ratios than the shoulders of paraplegics without impingement syndrome (P < 0.05). We concluded that shoulder muscle imbalance, with comparative weakness of the humeral head depressors (rotators and adductors), may be a factor in the development and perpetuation of rotator cuff impingement syndrome in wheelchair athletes.

Concentric and eccentric torque variations of the quadriceps femoris in patellofemoral pain syndrome

The purpose of this study was to investigate the extent of torque reduction in the quadriceps femoris in subjects complaining of patellofemoral pain syndrome compared to subjects with sound knees. Fifty-five patients (21 women and 34 men) and 30 healthy subjects (15 women and 15 men) took part in this study. Using the KINCOM isokinetic dynamometer, quadriceps torque was assessed at 30°/s, 60°/s, and 120°/s, both in the concentric and eccentric modes. Findings demonstrated a significant (P < 0·01) reduction of between 30% and 40% in the patients when compared with the control group. This reduction was not speed or mode-specific. Men were stronger than women by a margin of 22% and 14% for the concentric and eccentric modes in the control group. Parallel figures for the patellofemoral pain syndrome group were 25% and 17%. Good to high correlations were found between peak and average torque in both groups. There were no significant differences between the muscles referring to the dominant versus the non-dominant legs of the control group.