Original Research Journal of Sport Rehabilitation, 1995, 4, 244-252 O 1995 Human Kinetics Publ~shers, Inc. Scapular Muscle Strengthening Thomas Zmierski, Sam Kegerreis, and James Scarpaci The purposes of this study were (a) to determine the reliability of the Nicholas hand-held dynamometer for measuring scapular adductor strength and (b) to determine if isokineiic strengthening of the scapular adductors while horizontally abducting the shoulder is more effective than strengthening the scapular adductors while extending the shoulder. An isometric make test was used to determine scapular adductor strength before and after a 6-week training program. Intraclass correlation coefficient indicated high pretest and posttest reliability. The individuals who trained the scapular adductors while horizontally abducting the shoulder showed greater increases in mean force values (20.49 kg pretest to 31.74 kg posttest) than the group combining scapular adduction with shoulder extension (19.61 kg pretest and 25.52 kg posttest). ANOVA showed a significant interaction between group and time. It may be more effective to isokinetically strengthen the scapular adductors with shoulder horizontal abduction rather than shoulder extension as a combined movement. Strengthening the scapular stabilizers is a common goal in the treatment of various shoulder pathologies (2,5). Therapists often use isokinetic equipment to strengthen these muscles. It has been suggested that patients who have excessively protracted and abducted scapulae may benefit from strengthening the rhomboids and middle trapezius, in an attempt to reduce forward shoulder posture (6, 10). One technique commonly used to strengthen scapular adductors consists of grasping the lever arm of an isokinetic dynamometer with the elbow in complete extension, the shoulder flexed to 60, and the forearm in a neutral position. The patient alternately abducts and adducts the scapula as far as possible simultaneously flexing the elbow. During this movement the scapular adductors contract, but the brachioradialis is also active in flexing the elbow due to its insertion on the lateral supracondylaf ridge of the humerus (11). Also, depending on the position of the elbow, the brachialis and biceps brachia (recruited from 0-30" of elbow flexion) and the wrist flexors and extensors (recruited with increasing amounts of elbow flexion) will also actively contract to achieve full elbow flexion (11). The latissirnus dorsi, teres major, posterior deltoid, and long head of the triceps will be active secondary to their effect on shoulder extension (8). Thomas Zmierski and James Scarpaci are With The Community Hospital, Muaster, IN 46321. Sam Kegerreis is with the Krannert School of Physical Therapy, University of Indianapolis, 1400 E. Hama Ave., Indianapolis, IN 46227.
Scapular Muscle Strengthening 245 An alternative method to strengthen the scapular adductors using isokinetic equipment involves horizontally abducting the humerus at 90" of shoulder elevation while adducting the scapula. Again, the patient flexes the elbow during the movement but no shoulder extension is present, thus limiting the influence of the latissimus dorsi. During this movement the posterior deltoid, infraspinatus, and teres minor musculature are active secondary to their contribution to shoulder horizontal abduction (8). Both techniques result in active contraction of the scapular adductors; however, one training method also involves the shoulder extensors while the other involves the shoulder horizontal abductors. The purpose of this experimental study is to determine if there is a difference between these two techniques for increasing scapular adduction strength. Subjects Methods A sample of convenience was used consisting of 42 volunteers from a rehabilitation staff (occupational therapists, speech therapists, physical therapists, nurses, and their families) and patients seen at Community Hospital Outpatient Physical Therapy Department. There were 8 males and 34 females. The sample was randomly divided into two groups of 21 members each. Average age of Group A (scapular adduction without shoulder extension) was 37.2 years. Average age of Group B (shoulder extension with scapular adduction) was 40.8 years. All individuals were free from shoulder pathology and all provided informed consent. All individuals volunteered for a 6-week training program (three times a week for 6 weeks) totaling 18 sessions. Individuals signed in for each training session to ensure compliance. Of the 42 volunteers, 8 did not complete the entire study for various reasons including health problems and time constraints. Thirty-four participants remained, with 17 individuals in each training group. Procedures The individuals were separated into two groups and given specific written and verbal instructions on the number of repetitions, exercise intensity, joint positioning, stabilization, and standing position. The dominant arm was trained and tested in this study. The floor was clearly marked in 1-in. increments for both the vertical and horizontal axes. The individuals aligned the distal aspect of their toes with the vertical axis, and if they stood to their right of the isokinetic machine they aligned the outside of the left foot with the horizontal axis. If they stood to their left of the isokinetic machine they aligned their right foot with the horizontal axis. This ensured the same positioning for each training session. Group A subjects held onto a stationary cart to decrease excessive trunk flexion and extension, and Group B subjects held onto a stationary chair to decrease excessive trunk movement. Group A trained the scapular adductors with the elbow in full extension and the glenohumeral joint flexed 90" (measured goniometrically with full scapula abduction). They then fully adducted the scapula while maintaining 90" of shoulder elevation (see Figures 1 and 2). Group B trained the scapular adductors with the elbow in full extension, the forearm in a
246 Zmierski, Kegerreis, and Scarpaci neutral position, and the glenohumeral joint flexed 60' (measured goniometrically with the scapula fully abducted). They then fully adducted the scapula while simultaneously extending the glenohumeral joint (see Figures 3 and 4). Muscle tests of the rhomboids were performed with the Nicholas hand-held dynamometer (HHD) (Lafayette Instruments, Lafayette, IN) before the training sessions began. The HHD was used to determine scapular adductor force. The manual muscle test for scapular adduction strength (middle trapezius and rhomboid major and minor) is described by Daniels and Worthingham (3). The subject lay prone with the scapula and the humerus of the dominant arm exposed. The thorax and the lumbar area were stabilized with straps to prevent trunk rotation. Subjects rotated their head away from the side to be tested. The lateral border of the scapula (glenoid rim) was marked, and the lateral edge of the HHD force pad was aligned directly over the glenoid rim. The individual was told to adduct the scapula as far as possible, and an attempt was made to keep the vertebral border of the scapula parallel to the thoracic spinous processes. If severe medial or lateral scapula rotation was present, the tester asked the individual to adduct the scapula again without excessively rotating the scapula (1). An "isometric make test" was used as described by Bohannon (1) as a contraction in which the subject exerts maximal force against a stationary force pad (see Figure 5). The tester explained the procedure to the subject before testing. The subject held the contraction for 3 s, then took a 30-s rest period. This was repeated three times, and all three trials were recorded in kilograms. This method has been described by Diveta et al. (4) and by McMahon et al. (9) to calculate an intraclass correlation coefficient (ICC). The HHD was placed over the lateral border of the scapula and not the humerus to reduce multiple joint testing. The HHD was calibrated before each subject. The exercise programs were performed on the Biodex isokinetic dynamometer (Biodex Corporation, Shirley, NY). The researcher positioned the subject on the Biodex and limited the motion of the lever arm from full scapular abduction (limited by tension in the shoulder extensors and contact of the arm with the chest) to adduction (limited by tension in the anterior glenohumeral capsule, pectoralis major, and anterior deltoid) to ensure consistency and guarantee training through the entire range of motion (ROM). An arrow was placed on the lever arm shaft, and the exact position (measured in degrees) was recorded for starting and ending positions. Also the height of the power head was recorded so there would be no discrepancy of lever arm height. Finally the length of the lever arm was recorded. All of this information-group assignment, foot position, height of the power head, starting and ending angles, and length of the lever arm-was recorded on an index card with the individual's name and was noted each session so all positions would be identical. During the training session all subjects performed one set of 15 maximal repetitions for scapula adduction (7). Statistical Analysis A two-way mixed-model (Group x Time) ANOVA was used to analyze the data. To determine reliability of measures, the ICC was calculated using a formula of Portney and Watkins (12). This formula is appropriate when comparing the mean of several measures of an individual to the mean of the sample (in this case
Scapular Muscle Strengthening Figure 1 - Group A starting position. Figure 2 - Group A ending position. 247
Zmierski, Kegerreis, and Scarpaci 248 Figure 3 Figure 4 - Group B starting position. - Group B ending position.
Scapular Muscle Strengthening Figure 5 249 - Isometric test with hand-held dynamometer. The pretest ICC was.98 with a standard error of measurement (SEM) of M.99 kg. The posttest ICC was.96 with an SEM of f 1.70 kg. This indicates high reliability of both pretest and posttest measurement sessions. The pretest measurements in Group A ranged from 6.80 to 28.20 kg. The mean force was 20.49 f 5.87 kg. The pretest measurements in Group B ranged from 7.60 to 41.00 kg. The mean force value was 19.61 k 6.79 kg. The ANOVA showed a significant interaction between group and time (f= 10.73, p =.003). Because of this significant interaction, further analysis was done using simple main effects, which examine differences in one variable at each level of the other variables. The two groups were not significantly different at pretest (f =.16, p =.6955). The two groups were, however, significantly different at posttest (f=4. 8 9, ~=.0345). Group A showed significantimprovement from pretest to posttest (f = 65.46, p =.000), as did Group B (f = 44.29, p =.000). Figure 6 graphs the mean values for each group at pretest and posttest. Discussion Both training groups made gains in isometric scapular adductor strength; however, Group A made a larger gain (11.24 kg). It is possible that the latissimus dorsi was more active in Group B since shoulder extension was performed with scapular adduction. Thus, when the isometric strength evaluation was performed and the latissimus dorsi activity was eliminated, there was not as great a strength improvement in Group B. It appears that performing shoulder extension with
1 250 Zrnierski, Kegerreis, and Scarpaci Pre test OGroup A a Group B Post test Figure 6 - Comparison of mean force values. scapular adduction primarily trained the latissimus dorsi and did not offer a significant stimulus to strengthen the scapular adductors. Diveta and colleagues (4) showed that the position of the scapula is not related to isometric strength of the pectoralis minor, the middle trapezius, or the pectoralis minorlmiddle trapezius strength ratio. They performed a static measurement of scapula position and compared this measurement to muscle force production of the two aforementioned groups. They did not measure scapula position before and after a training program for the scapula adductors. It would be interesting to note scapula position before and after such a training program to see if there is a change. Scapular orientation is also a factor to consider when strengthening the scapular adductors. Even though during the testing procedures a neutral scapular position was maintained, during the dynamic training an individual may have had more medial or lateral rotation of the scapula. This may have resulted in more recruitment of the middle trapezius with lateral rotation of the scapula or more recruitment of the rhomboid with medial rotation of the scapula (3). Since the isometric make test assessed the strength of the scapular adductors as a whole, we did not attempt to differentiate between the rhomboids or the middle trapezius. Our results suggest that it is more effective to isokinetically strengthen the scapular adductors by utilizing the movements of scapular adduction with horizontal shoulder abduction rather than scapular adduction with shoulder extension. The efficiency of the latissimus is reduced in shoulder horizontal abduction possibly resulting in greater recruitment of the middle trapezius, rhomboid major,
Scapular Muscle Strengthening 251 and rhomboid minor. If it is the therapist's intent to strengthen the scapular adductors, it would be advantageous to utilize shoulder horizontal abduction. Therapists strengthen the scapular adductors for various reasons. Impingement of the anterior structures of the shoulder secondary to abnormal scapular motion or rhythm is one of the pathologies that may benefit from such a program. If the therapist can train the individual to actively contract the scapular adductors during elevation of the shoulder, this may reduce compression of the subacromial structures. Individuals who have pain in the midscapular area from muscular fatigue may also benefit from this program. We often see patients who have midscapular pain after prolonged sitting or standing. This pain may be due to weakness of the scapular adductors resulting in chronic strain of the muscles or to an increase in thoracic kyphosis, which may cause pain from numerous tissues being placed under tension in the thoracic spine. We realize that in today's cost-conscious health care environment it may be impractical for a patient to return to the clinic several times a week to perform an isokinetic exercise. A follow-up study in which subjects perform scapular adduction exercise with free weights at home would be interesting. This may prove not only more cost effective but more convenient for the patient as well. References 1. Bohannon, R.W. The clinical measurement of strength. Clin. Rehabil. 1:s-16, 1987. 2. Brunet, M.E., R.J. Haddad, and E. Porche. Rotator cuff impingement syndrome in sports. Phys. Sportsmed. 10536-93, 1982. 3. Daniels, L., and C. Worthingham. Muscle Testing Techniques of Manual Examination. Philadelphia: Saunders, 1986. 4. Diveta, J., M.L. Walker, and B. Skibinski. Relationship between performance of selected scapular muscles and scapular abduction in standing subjects. Phys. Ther. 70(8): 15-24, 1990. 5. Fowler, P. Swimmer problems. J. Sports Med. 7:141-142, 1979. 6. Greipp, J.F. Swimmers shoulder: The influence of flexibility and weight training. Phys. Sportsmed. 13:92-105, 1985. 7. Jenkins, W., M. Thackabeny, and C. Killian. Speed specific isokinetic training. J. Orthop. Sports Phys. Ther. 6:181-183, 1984. 8. Kendall, F.P., and E.K. McCreary. Muscles Testing and Function (3rd ed.). Baltimore: Williams & Wilkins, 1983. 9. McMahon, L.M., R.G. Burdett, and S.L. Whitney. Effects of muscle group and placement site on reliability of hand held dynamometer on strength measurements. J. Orthop. Sports Phys. Ther. 15(5):236-242, 1992. 10. Neviaser, R. Painful conditions affecting the shoulder. Clin. Orthop. Rel. Res. 173:63-69, 1983. 11. Perry, J. Normal upper extremity kinesiology. Phys. Ther. 58:265-278, 1978. 12. Portney, W., and N.P. Watkins. Foundation of Clinical Research: Applications to Practice. E. Norwalk, CT: Appleton and Lange, 1993.
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