Measuring Eccentric Strength of the Shoulder External Rotators Using a Handheld Dynamometer: Reliability and Validity

CONTEXT

Shoulder strength assessment plays an important role in the clinical examination of the shoulder region. Eccentric strength measurements are of special importance in guiding the clinician in injury prevention or return-to-play decisions after injury.

OBJECTIVE

To examine the absolute and relative reliability and validity of a standardized eccentric strength-measurement protocol for the glenohumeral external rotators.

DESIGN

Descriptive laboratory study.

SETTING

Testing environment at the Department of Rehabilitation Sciences and Physiotherapy of Ghent University, Belgium.

PATIENTS OR OTHER PARTICIPANTS

Twenty-five healthy participants (9 men and 16 women) without any history of shoulder pain were tested by 2 independent assessors using a handheld dynamometer (HHD) and underwent an isokinetic testing procedure.

INTERVENTION(S)

The clinical protocol used an HHD, a DynaPort accelerometer to measure acceleration and angular velocity of testing 30°/s over 90° of range of motion, and a Biodex dynamometer to measure isokinetic activity.

MAIN OUTCOME MEASURE(S)

Three eccentric strength measurements: (1) tester 1 with the HHD, (2) tester 2 with the HHD, and (3) Biodex isokinetic strength measurement.

RESULTS

The intratester reliability was excellent (0.879 and 0.858), whereas the intertester reliability was good, with an intraclass correlation coefficient between testers of 0.714. Pearson product moment correlation coefficients of 0.78 and 0.70 were noted between the HHD and the isokinetic data, showing good validity of this new procedure.

CONCLUSIONS

Standardized eccentric rotator cuff strength can be tested and measured in the clinical setting with good-to-excellent reliability and validity using an HHD.

Does an in-season detraining period affect the shoulder rotator cuff strength and balance of young swimmers?

Imbalance in shoulder rotator muscles is a well-documented problem in swimmers, and it is important to implement land-based strength training programs. Meanwhile, the effects of a detraining period on swimmers' shoulder rotator muscles are unknown. The purpose of this study was to analyze the effects of a strength training program and detraining on the strength and balance of shoulder rotator cuff muscles in young swimmers, despite the continuity of usual water training. An experimental group (n = 20) and a control group (n = 20) of young male swimmers with the same characteristics (age, body mass, height, training volume, and maturational state) were evaluated. In both groups, the peak torques of shoulder internal (IR) and external (ER) rotators were assessed during preseason, midseason (16 weeks), and postseason (32 weeks). The experimental group underwent a strength training regimen from baseline to 16 weeks and a detraining period from 16 to 32 weeks. Concentric action at 60°·s-1 and 180°·s-1 was measured using an isokinetic dynamometer. The ER/IR strength ratios were obtained. At 60°·s-1, there were significant increments in IR strength and the ER/IR ratio in both shoulders. This trend was the same throughout the competitive season. The tendency was the same at 180°·s-1 because training effects were noted primarily in IR and ER/IR ratios. Moreover, the absence of land-based strength training, from 16 to 32 weeks, revealed a reduction in the ER/IR ratio values in both shoulders. Our findings suggest that young swimmers' coaches should use dry-land strength training protocols, and that it is recommended that these should be conducted on a regular basis (during the whole season).

Muscle activity pattern of the shoulder external rotators differs in adduction and abduction: an analysis using positron emission tomography

BACKGROUND

The muscle activity pattern during shoulder external rotation has not been fully clarified. This study aimed to determine the activities involved in external rotation in the adducted and abducted positions using positron emission tomography (PET).

METHODS

Seven healthy volunteers underwent PET examinations after performing external rotation using an elastic band at both 0° and 90° of shoulder abduction in the frontal plane. External rotation exercise was performed before and after injection of fluorine 18 fluorodeoxyglucose, which was followed by PET examination. The protocols for external rotation exercise were identical between the 2 shoulder positions. To obtain control data, PET examination was also performed under resting conditions. The order of these 3 PET examinations was randomized, and they were performed at intervals of 1 week or greater. Each PET image was fused to the corresponding magnetic resonance image to identify each shoulder muscle. After this, the standardized uptake value was calculated in each muscle and was compared between the 2 shoulder positions.

RESULTS

The infraspinatus showed the greatest muscle activity during external rotation at 0° of abduction, whereas the teres minor showed the greatest activity at 90° of abduction. The teres minor-infraspinatus ratio at 90° of abduction (mean ± SD, 1.21 ± 0.23) was significantly higher than that at 0° of abduction (0.84 ± 0.15) (P < .01).

CONCLUSION

The infraspinatus and teres minor are the main shoulder external rotators. The teres minor is more important as an external rotator in abduction than in adduction.

Isometric shoulder strength reference values for physically active collegiate males and females

Background:

It is common clinical practice to assess muscle strength during examination of patients following shoulder injury or surgery. Strength comparisons are often made between the patient’s injured and uninjured shoulders, with the uninjured side used as a reference without regard to upper extremity dominance. Despite the importance of strength measurements, little is known about expected normal baselines of the uninjured shoulder. The purpose of this study was to report normative values for isometric shoulder strength for physically active college-age men and women without history of shoulder injury.

Methods:

University students—546 males (18.8 ± 1.0 years, 75.3 ± 12.2 kg) and 73 females (18.7 ± 0.9 years, 62.6 ± 7.0 kg)—underwent thorough shoulder evaluations by an orthopaedic surgeon and completed bilateral isometric strength measurements with a handheld dynamometer. Variables measured included internal rotation, external rotation, abduction, supine internal rotation and external rotation at 45°, and lower trapezius in prone flexion.

Results:

Significant differences were found between the dominant and nondominant shoulder for internal rotation, internal rotation at 45°, abduction, and prone flexion in males and in internal rotation at 45° and prone flexion for females (P ≤ 0.01).

Can glenohumeral joint isokinetic strength and range of movement predict injury in professional rugby league

OBJECTIVE

To isokinetically record shoulder strength scores and range of motion in a professional rugby league squad. To prospectively monitor injuries over a season looking for associations between measured variables and injury.

DESIGN

A cohort study design involving prospective screening of risk factors with subsequent injury surveillance.

SETTING

University Sports Science Laboratory and Professional Rugby League Club.

PARTICIPANTS

All players participating in the clubs reserve team squad for the 2011 season (n = 20).

MAIN OUTCOME MEASURES

Concentric (Con) and eccentric (Ecc) peak torque values; ratio of Ecc internal rotation IR to Con external rotation ER, also known as the dynamic control ratio (DCR), shoulder range of IR and ER.

RESULTS

Eight players (36%) received a total of eleven injuries over the season. There were no statistically significant differences between injured and non-injured shoulders. IR range of movement was significantly lower in injured versus non-injured groups with left (p = 0.022) and right (p = 0.024). Left IR range of movement was predictive of injury using binary logistic regression (p = 0.046). No isokinetic strength parameters reached statistical significance (p > 0.05) for prediction of injury; however size effects were apparent for reduced con IR of the left shoulder and Ecc IR of both shoulders.

CONCLUSION

Reduced shoulder IR range appears predictive of future shoulder injury although caution is drawn due to small participant numbers. Injury prevention strategies for rugby league players should include exercises to improve shoulder IR and possibly Ecc IR strength.

Rotator Cuff Weakness Is Not a Risk Factor for First-Time Anterior Glenohumeral Instability

Background:

Shoulder instability is a common problem in young athletes and can lead to pain and decreased ability to participate in high-level activities. Little is known about the modifiable risk factors for glenohumeral joint instability.

Hypothesis:

Isometric shoulder strength at baseline would be a modifiable risk factor associated with subsequent first-time anterior instability events.

Study Design:

Cohort study.

Methods:

Study participants were freshmen entering the United States Military Academy in June 2006. All participants completed bilateral isometric strength evaluations with a hand-held dynamometer at baseline upon entry into the study. Variables measured included internal and external rotation at 0° (IR0, ER0) and internal and external rotation at 45° of abduction (IR45, ER45). All subjects were followed for subsequent glenohumeral joint instability events until graduation in May 2010. Independent t tests were used to analyze the data.

Results:

Baseline strength data were available for 1316 shoulders with no prior history of instability, of which 26 went on to have an acute first-time anterior shoulder instability event while the individuals were at the academy. There were no significant differences in mean strength between shoulders that did not go on to develop instability (uninjured; n = 1290) and those that did develop anterior instability (injured; n = 26). The mean strength values in pounds of force for uninjured and injured shoulders, respectively, were as follows: IR0 (49.80 vs 49.29; P = .88), ER0 (35.58 vs 33.66; P = .27), IR45 (47.38 vs 46.93; P = .88), and ER45 (40.08 vs 38.98; P = .59).

Conclusion:

No association was found between isometric shoulder strength measures at baseline and subsequent first-time anterior glenohumeral joint instability within the high-risk athletic population studied in this prospective cohort.

Profiling the isokinetic shoulder rotator muscle strength in 13- to 36-year-old male and female handball players

OBJECTIVES

To evaluate the external (ER) and internal rotator (IR) muscles' isokinetic peak torque and conventional and functional strength ratios in handball players and controls of different ages.

DESIGN

Cross-sectional and descriptive analysis.

SETTING

Exercise Physiology Laboratory.

PARTICIPANTS

A total of 228 participants (108 athletes and 120 controls) were divided into five groups according to age, ranging from 13 to 36 years old.

MAIN OUTCOME MEASURES

Isokinetic tests were performed concentrically at 60 and 300 deg s(-1) and eccentrically at 300 deg s(-1).

RESULTS

The differences between the athletes and controls regarding the peak torque of the ER and IR muscles were significant in males older than 18 years. The peak torque of the IR and ER muscles increased significantly across age in male athletes, but not in female athletes, except in the case of ER peak torque, which differed significantly between 13 and 16 years old. The female athletes presented higher conventional ratios (0.81 ± 0.07) than males (0.66 ± 0.08). Values represent means and standard deviations. Athletes and controls showed mean functional strength ratios below 1.0.

CONCLUSIONS

Although there were no muscular ratio differences between the athletes and the controls, their ratio values were below the literature-recommended reference values to prevent shoulder injuries.

Preseason shoulder strength measurements in professional baseball pitchers: identifying players at risk for injury

BACKGROUND

The ability to identify pitchers at risk for injury could be valuable to a professional baseball organization. To our knowledge, there have been no prior studies examining the predictive value of preseason strength measurements.

HYPOTHESIS

Preseason weakness of shoulder external rotators is associated with increased risk of in-season throwing-related injury in professional baseball pitchers.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 2.

METHODS

Preseason shoulder strength was measured for all pitchers in a professional baseball organization over a 5-year period (2001-2005). Prone internal rotation (IR), prone external rotation (PER), seated external rotation (SER), and supraspinatus (SS) strength were tested during spring training before each season. The players were then prospectively followed throughout the season for incidence of throwing-related injury. Injuries were categorized on an ordinal scale, with no injury, injury treated conservatively, and injury resulting in surgery delineated 0, 1, and 2, respectively. Subset analyses of shoulder injuries and of players with prior surgery were also performed. The association between strength measurements and injury was analyzed using Spearman rank correlation.

RESULTS

A statistically significant association was observed for PER strength (P = .003), SER strength (P = .048), and SS strength (P = .006) with throwing-related injury requiring surgical intervention. Supraspinatus strength was also significantly associated with incidence of any shoulder injury (P = .031). There was an association between the ratio of PER/IR strength and incidence of shoulder injury (P = .037) and some evidence for an association with overall incidence of throwing-related injury (P = .051). No associations were noted in the subgroup of players with prior surgery.

CONCLUSION

Preseason weakness of external rotation and SS strength is associated with in-season throwing-related injury resulting in surgical intervention in professional baseball pitchers. Thus, preseason strength data may help identify players at risk for injury and formulate strengthening plans for prevention.

Muscle activation and perceived loading during rehabilitation exercises: comparison of dumbbells and elastic resistance

BACKGROUND

High-intensity resistance training plays an essential role in the prevention and rehabilitation of musculoskeletal injuries and disorders. Although resistance exercises with heavy weights yield high levels of muscle activation, the efficacy of more user-friendly forms of exercise needs to be examined.

OBJECTIVE

The aim of this study was to investigate muscle activation and perceived loading during upper-extremity resistance exercises with dumbbells compared with elastic tubing.

DESIGN

A single-group, repeated-measures study design was used.

SETTING

Exercise evaluation was conducted in a laboratory setting.

PARTICIPANTS

Sixteen female workers (aged 26-55 years) without serious musculoskeletal diseases and with a mean neck and shoulder pain intensity of 7.8 on a 100-mm visual analog scale participated in the study.

MEASUREMENTS

Electromyographic (EMG) activity was measured in 5 selected muscles during the exercises of lateral raise, wrist extension, and shoulder external rotation during graded loadings with dumbbells (2-7.5 kg) and elastic tubing (Thera-Band, red to silver resistance). The order of exercises and loadings was randomized for each individual. Electromyographic amplitude was normalized to the absolute maximum EMG amplitude obtained during maximal voluntary isometric contraction and exercise testing. Immediately after each set of exercise, the Borg CR10 scale was used to rate perceived loading during the exercise.

RESULTS

Resistance exercise with dumbbells as well as elastic tubing showed increasing EMG amplitude and perceived loading with increasing resistance. At the individually maximal level of resistance for each exercise-defined as the 3 repetitions maximum-normalized EMG activity of the prime muscles was not significantly different between dumbbells (59%-87%) and elastic tubing (64%-86%). Perceived loading was moderately to very strongly related to normalized EMG activity (r=.59-.92). Limitations The results of this study apply only for exercises performed in a controlled manner (ie, without sudden jerks or high acceleration).

CONCLUSIONS

Comparably high levels of muscle activation were obtained during resistance exercises with dumbbells and elastic tubing, indicating that therapists can choose either type in clinical practice. The Borg CR10 can be a useful aid in estimating intensity of individual rehabilitation protocols.

Shoulder functional ratio in elite junior tennis players

OBJECTIVE

To evaluate shoulder rotation strength and compare the functional ratio between shoulders of elite junior tennis players.

DESIGN

This cross-sectional study evaluated muscular rotation performance of 40 junior tennis players (26 male and 14 female) with an isokinetic dynamometer.

MAIN OUTCOME MEASURES

Strength variables of external (ER) and internal rotators (IR) in concentric and eccentric modes were considered. For the peak torque functional ratio, the eccentric strength of the ER and the concentric strength of the IR were calculated.

RESULTS

All variables related to IR were significantly higher on the dominant compared to the non-dominant side in males and females (p<0.05), but only boys exhibited this dominance effect in ER (p<0.05 and p<0.001). Regarding functional ratios, they were significantly lower for the dominant shoulder (p<0.001) and below 1.00 for both groups, indicating that the eccentric strength of the ER was not greater than the concentric strength of the IR.

CONCLUSION

Elite junior tennis players without shoulder injury have shoulder rotation muscle strength imbalances that alter the normal functional ratio between rotator cuff muscles. Although these differences do not seem to affect the athletic performance, detection and prevention with exercise programs at an early age are recommended.