Reproducibility of isometric shoulder protraction and retraction strength measurements in normal subjects and individuals with winged scapula

Intra- and interrater reliability of belt-stabilized hand-held dynamometer in scapular protraction strength tests in individuals with shoulder pain

PURPOSE

Scapular protraction strength can be evaluated using a hand-held dynamometer (HHD). However, it is necessary to measure the reliability of HHD in individuals with shoulder pain and to minimize the limitations related to the evaluator and the low methodological quality cited in previous studies. This study assessed, with methodological enhancement, the intra- and interrater reliability of belt-stabilized HHD in the assessment of scapular protraction strength in individuals with shoulder pain.

METHOD

Fifty individuals with unilateral symptoms of subacromial pain syndrome (20 men, aged 40.5 ± 15.3 years) were evaluated in two sessions using the belt-stabilized HHD for maximum isometric strength of scapular protraction with the individual in the sitting and supine positions. Reliability values were obtained using the intraclass correlation coefficient with the standard error of measurement (SEM and %SEM) and the minimal detectable change (MDC).

RESULTS

The intra- and interrater HHD reliability were excellent for all measurements ranging from 0.88 to 0.96 (SEM = 2.0-4.0 kg; %SEM 12 to 17; MDC = 6-11 kg).

CONCLUSION

Belt-stabilized HHD is reliable for the assessment of scapular protraction strength in individuals with subacromial pain syndrome in both the sitting and supine positions.

Validity and reliability of a low-cost dynamometer to assess maximal isometric strength of upper limb

Muscle imbalance and deficit are key parameters for guiding rehabilitation and sports sessions and avoiding injuries. However, the high cost and non-portable nature of most instruments employed for muscle strength assessment frequently hamper an affordable evaluation in field conditions. This study evaluated the validity and reliability of a low-cost digital dynamometer to assess the maximal isometric strength of upper limb muscles. Fourteen physically active volunteers performed the main movements of the upper limb at maximal isometric strength: flexion-extension, internal-external rotation and abduction-adduction of the shoulder; and flexion-extension of both elbow and wrist. Validity was examined by comparing the strength values from the low-cost digital dynamometer and those measured by an isokinetic dynamometer, assumed as the gold standard. The correlation between both devices was perfect (r > 0.913), while Bland-Altman plots showed absolute agreement between both devices, the maximum range of the values of bias was -0.99-1.00 N in wrist extension. Inter-tester and intra-tester reliability were excellent for all movements (ICC ≥ 0.855). The low-cost digital dynamometer showed strong validity and excellent reliability in assessing maximal isometric strength during the main movements of the upper limb. Professionals may use it for an affordable isometric muscle strength assessment in field situations.

Comparison of Shoulder Protraction Strength and Electromyography Activity of Serratus Anterior and Pectoralis Major in Subjects With or Without a Winged Scapula

CONTEXT

A winged scapula (WS) is associated with faulty posture caused by weakness of the serratus anterior (SA), which mainly acts as a scapular stabilizer muscle. It is important to accurately assess and train the SA muscle with a focus on scapula stabilizers during musculoskeletal rehabilitation of individuals with a WS.

OBJECTIVE

The authors examined muscle activity in the SA and pectoralis major (PM), upper trapezius (UT), and anterior deltoid (AD) as well as shoulder protraction strength during isometric shoulder protraction in individuals with and without a WS.

DESIGN

Cross-sectional study.

SETTING

A clinical biomechanics laboratory.

PARTICIPANTS

In total, 27 males with no shoulder, neck, or upper-extremity pain participated.

MAIN OUTCOME MEASURES

Isometric shoulder protraction strength was collected and surface electromyography used to measure the activity of the SA, PM, UT, and AD muscles and selective SA activity ratio to other shoulder muscles.

RESULTS

Electromyography activity of the SA muscle and shoulder protraction strength were significantly lower in individuals with a WS compared with the non-WS group (P < .05). In contrast, PM muscle activity and the PM-to-SA, UT-to-SA, and AD-to-SA ratios were significantly greater in individuals with a WS than in individuals without winging (P < .05).

CONCLUSIONS

Isometric shoulder protraction for measuring SA strength in individuals with a WS should focus on isolated muscle activity of the SA, and SA strengthening exercises are important for individuals with a WS.

Electromyographic activity of the serratus anterior and pectoralis major during isometric scapular protraction at different resistance intensities in subjects with and without a winged scapula

BACKGROUND

During maximal isometric protraction, it is important to determine the optimal resistance intensity in subjects with a winged scapula, for inducing isolated activity of the serratus anterior against the pectoralis major, which is activated as a synergistic muscle. The aim of the present study was to determine electromyographic activities of the serratus anterior and pectoralis major muscles during isometric shoulder protraction at different levels in subjects with and without a winged scapula.

METHODS

Thirty male subjects performed isometric shoulder protraction in a sitting position at different resistance intensity levels (100%, 80%, and 60% of maximal protraction strength). Surface electromyographic data of the serratus anterior and pectoralis major muscles were gathered simultaneously using fixed instrumentation to measure isometric shoulder protraction.

FINDINGS

Muscle activity of the serratus anterior in subjects without a winged scapula was significantly greater than that of subjects with a winged scapula across all three conditions, whereas muscle activity of the pectoralis major was lower in subjects without a winged scapula. In addition, winged scapula muscle activity corresponding to maximal protraction was significantly greater than that in the submaximal condition.

INTERPRETATION

In a clinical setting, submaximal resistance can be more optimal than maximal effort during isometric shoulder protraction in individuals with a winged scapula.

Concurrent validity of handheld dynamometer measurements for scapular protraction strength

BACKGROUND

Handheld dynamometers (HHD) provide quick and low-cost assessments of muscle strength and their use has been increasing in clinical practice. There is no available data related to the validity of HHD for this measurement.

OBJECTIVE

To verify the concurrent validity of scapular protraction measurements using an HHD.

METHODS

Individuals with traumatic anterior glenohumeral instability were allocated in Instability Group (n=20), healthy swimmers were allocated in Athletes Group (n=19) and healthy subjects were allocated in Sedentary Group (n=21). Concurrent validity was verified by the Pearson correlation test between HHD and isokinetic measurements. The agreement between instruments was verified by Bland-Altman plots, for each of the two HHD positions.

RESULTS

A moderate correlation was observed between seated (r=0.59) and lying supine HHD (r=0.54) and isokinetic dynamometer measurements for the all groups. Separated group analysis exhibited a strong correlation between seated HHD and isokinetic dynamometer measurements in the Instability Group (r=0.80), Sedentary Group (r=0.79) and Athletes Group (r=0.76). The Bland-Altman plot showed greater agreement in the seated position than the lying supine position when comparing measurements with the HHD and isokinetic in both the general sample and separated groups.

CONCLUSION

The HHD may be considered a valid tool for assessing scapular protraction muscle strength among healthy athletes, non-athletes and subjects with shoulder instability. We recommend to assess subjects in the seated position and to be aware that the HHD tends to overestimate the peak force, compared with the gold-standard isokinetic dynamometer.

Effects of horizontal shoulder abduction and adduction on the activity and strength of the scapular protractors

Increased activity of the serratus anterior (SA) muscle combined with decreased activity of the pectoralis major (PM) muscle during scapular protraction exercise is a widely used method for selective strengthening of the former muscle. However, the role played by the PM during maximal scapular protraction remains unclear. The objective of our study was to investigate the effects of horizontal shoulder abduction (decreasing PM activity) and adduction (increasing activity) on the strength and activity of the scapular protractors (the SA and PM) during maximal protraction. Twenty-nine healthy males performed maximal scapular protraction combined with horizontal shoulder abduction or adduction. The strength and activity of the PM and SA decreased significantly (both p < 0.01) during maximal scapular protraction combined with horizontal shoulder abduction, compared with maximal scapular protraction alone, but increased significantly (both p < 0.01) when maximal scapular protraction was combined with horizontal shoulder adduction. We thus conclude that the PM stabilizes the activated SA during maximal scapular protraction, which effectively increases SA activity and scapular protraction strength in the serratus punch posture.