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The ‘empty can’ and ‘full can’ tests do not selectively activate supraspinatus
Available online at www.sciencedirect.com
Journal of Science and Medicine in Sport 12 (2009) 435–439
Original paper
The ‘empty can’ and ‘full can’ tests do not selectively activate supraspinatus Craig E. Boettcher a,∗ , Karen A. Ginn a , Ian Cathers b a
Discipline of Biomedical Science, Faculty of Medicine, The University of Sydney, Australia b Faculty of Health Sciences, The University of Sydney, Australia
Received 26 June 2008; received in revised form 28 August 2008; accepted 1 September 2008
Abstract Based on previous electromyographic studies the ‘empty can’ (EC) and ‘full can’ (FC) tests have been promoted as being able to isolate activity to supraspinatus and are therefore diagnostic of supraspinatus dysfunction. However, there is evidence to suggest that these positions do not selectively activate supraspinatus, and that they may have poor diagnostic accuracy, bringing into question the validity of these tests. Due to limitations in the original EMG papers describing the EC and FC tests the current study aimed to further examine shoulder muscle activity during these tests to determine their ability to selectively activate supraspinatus. EMG activity was recorded from 13 muscles in 15 normal subjects while performing these two tests. Results showed that during the EC and FC muscle tests nine and eight other shoulder muscles, respectively, were equally highly activated as supraspinatus. It was concluded from these results that the EC and FC tests do not primarily activate supraspinatus with minimal activation from other shoulder muscles and therefore, do not satisfy basic criteria to be valid diagnostic tools for supraspinatus pathology. Therefore, these tests should not be interpreted as definitive tests for the clinical diagnosis of supraspinatus pathology. They may, however, be beneficial during shoulder muscle strengthening programs. © 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. Keywords: Shoulder; Supraspinatus; Empty can test; Full can test; Rotator cuff
1. Introduction Shoulder disorders are common and are often the result of rotator cuff tendinopathy, with the supraspinatus tendon most often affected.1–3 As a result clinical tests aimed at isolating activity in the supraspinatus musculotendinous unit to diagnose pathology4–6 and to strengthen the supraspinatus muscle7,8 have been developed. Jobe and Moynes (1982) first described a position of 90◦ arm abduction, 30◦ horizontal flexion, and full shoulder internal rotation, with resistance being applied to elevation, now known as the “empty can” (EC), “Jobe’s” or “supraspinatus” test (Fig. 1a). They claimed that with this test position the activity of the supraspinatus ‘can be isolated to some degree’5 . However, to support this conclusion, they reported only traces of raw EMG signal from all the rotator cuff muscles in only one subject and without further analysis. ∗
Corresponding author. E-mail address: [email protected] (C.E. Boettcher).
Further to this in 1996 Kelly et al. compared the EC test to a modification involving 45◦ external rotation instead of full internal rotation, termed the “full can” (FC) test (Fig. 1b). They found this position to activate the supraspinatus to a similar level to the EC test, but to activate the infraspinatus to a lesser degree. They also argued that the FC position would be less pain provoking than the EC test by avoiding the impingement position caused by the greater tuberosity rotating under the coraco-acromial arch during internal rotation, and thus would be a more reliable test of supraspinatus function. Although these researchers recorded from eight shoulder muscles they failed to report on the relative level of activity between the supraspinatus and muscles other than infraspinatus. Largely based on the results of these two studies the EC and FC tests have become commonly used clinical tests for diagnosing supraspinatus pathology. Current orthopedic physical assessment textbooks describe these tests as definitive for supraspinatus pathology9–11 —“the empty can test is a manual resistive test to assess the integrity of the
1440-2440/$ – see front matter © 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jsams.2008.09.005
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in the clinical evaluation of supraspinatus pathology. Based on the premise that to be valid diagnostic tools to identify supraspinatus pathology, the EC and FC tests must be capable of primarily activating supraspinatus with minimal activation from other shoulder muscles,6 the aim of this study was to examine muscles from each of the major muscle groups of the shoulder during performance of the EC and FC tests to assess their ability to selectively activate supraspinatus.
2. Materials and methods
Fig. 1. Illustration of the “empty can” (EC) test (a) and “full can” (FC) test (b).
supraspinatus muscle-tendon unit”.11 However, the results of the EMG studies by Jobe et al. and Kelly et al. provide insufficient data to support the conclusion that the EC and/or FC tests isolate supraspinatus activity. Indeed, EMG evidence exists to suggest that the EC and/or FC tests highly activate deltoid,8,12,13 infraspinatus,12,14,15 subscapularis8,15 and serratus anterior12,15 as well as supraspinatus. In addition to the EMG evidence indicating that the EC and FC tests do not selectively activate supraspinatus, clinical studies raise doubt about the ability of these tests to determine supraspinatus pathology. Studies examining the diagnostic validity of the EC and FC tests using surgical and/or MRI findings to confirm supraspinatus pathology, indicate that they have poor to moderate specificity16–18 and accuracy.19,20 Tennent et al.21 makes the observation that many clinical tests lack an evidence base and have become, and remain, a part of the examination procedure through teaching without reference to the original descriptive papers. In light of weak EMG evidence to indicate that the EC and FC tests selectively activate supraspinatus, that other muscles are highly activated during these tests, and clinical studies questioning their validity as tests of supraspinatus pathology, it would seem that this may be the case for the EC and FC tests. Therefore, this comprehensive EMG study assessing shoulder muscle activation during the EC and FC tests was designed to determine the validity of the use of these tests
The data for the EC and FC tests examined in this paper are a subset of those from a previous study undertaken in our lab.15 Further details to those described here regarding experimental arrangements and procedures are provided in this earlier paper. Nine males and six females subjects with normal dominant shoulder function were recruited for this study (mean age 28.4 years, range 19–47 years). Testing was performed on normal subjects as it was determined that interpretation of the EC and FC tests in patients with shoulder pathology has to be based on an accurate understanding of normal muscle activation. This is in keeping with previous EMG studies examining these tests.5,6 The study was approved by The University of Sydney Human Research Ethics Committee and all subjects signed a University of Sydney approved informed consent form prior to participation. Electromyographic data were collected simultaneously from 12 shoulder muscles using a combination of surface and intramuscular fine-wire electrodes. Intramuscular electrodes were used to record activity from supraspinatus, infraspinatus, subscapularis, middle trapezius, lower trapezius, serratus anterior and latissimus dorsi. Surface electrodes were used for upper trapezius, anterior deltoid, middle deltoid, posterior deltoid and pectoralis major. Surface and intramuscular electrodes were attached to amplifiers (two Iso-DAM 8 amplifiers, World Precision Instruments). EMG signals were amplified (gain = 100) and filtered (HP = 10 Hz, LP = 1 kHz). Data was acquired on a personal computer with a 16 bit analog to digital converter (1401, Cambridge Electronics Design) at a sampling rate of 3571 Hz using Spike2 software (version 4.00, Cambridge Electronics Design) and stored for later off-line analysis. The test positions of abduction in the scapular plane (30◦ horizontal flexion) with internal rotation (EC position) and abduction in the scapular plane with external rotation (FC position) were examined in random order along with 13 other shoulder test positions as part of the larger study.15 Manual resistance was applied by one of the researchers at the wrist. Each contraction was held for 5 s with a gradual increase of resistance over 1 s, a sustained maximal contraction with resistance for 3 s, and a gradual release over the final second. Three repetitions of each test were performed, with a minimum rest interval of 30 s between each repetition. To ensure consistency of positioning during each isometric
C.E. Boettcher et al. / Journal of Science and Medicine in Sport 12 (2009) 435–439
test, subjects were closely monitored to ensure they did not attempt compensatory movements of the scapula or trunk. If it was determined that a test was being done incorrectly it was ceased and repeated. All raw EMG data was visually inspected and a confirmatory power spectral analysis performed when there was doubt regarding the validity of the signal from a channel. As a result of inspection 41 (3.5%) of the 1170 individual trials (15 subjects × 2 muscle tests × 13 muscle sites × 3 trials) were discarded due to movement artifact or a channel being lost during the experiment. These data were excluded from further analysis. The EMG signals were high pass filtered (20 Hz, 8th order Butterworth), rectified, and low pass filtered (3 Hz, 8th order Butterworth). The maximum value of the resulting EMG envelope was determined and this was averaged across the trials for each test. Values were normalised using the maximum activity level (MVC) generated for each muscle across the four isometric Shoulder Normalisation Tests recently validated to generate maximum activity in all muscles tested in this study.15 These tests were: abduction at 90◦ in full internal rotation, internal rotation at 90◦ abduction, flexion at 125◦ with scapula resistance, and horizontal adduction at 90◦ flexion. A two-way repeated measures ANOVA (with muscles and tests as factors) was undertaken (Statistica version 7.1, StatSoft). This was followed by Tukey post hoc tests. Statistical significance was accepted at a probability less than 0.05.
3. Results The mean activation levels (95% confidence levels) for the 13 shoulder muscle sites tested for both the EC and FC tests are illustrated in Fig. 2. Both tests activated supraspinatus and nine other muscle sites to above 70% of their maxima (Fig. 2).
Fig. 2. Activation levels for the 13 muscles in the “empty can” and “full can” tests. Bars indicate 95% confidence intervals.
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Results of the ANOVA indicated that there is very strong evidence of a difference in activation levels across all muscles (F(12,168) = 34.8; p < 0.001), with post hoc tests revealing that the mean activity in supraspinatus was only higher than that in latissimus dorsi, pectoralis major and lower subscapularis (p < 0.001), with no significant difference between levels of supraspinatus activity and the other muscles tested. While there was no evidence of a difference in the muscle activation levels between the EC and FC tests (F(1,14) = 2.10; p = 0.17), there was very strong evidence of a difference in muscle activation pattern in the two tests (F(12,168) = 3.33; p < 0.001) which post hoc testing revealed to be only for posterior deltoid (p < 0.05).
4. Discussion The results of this study have definitively determined that the EC and FC tests do not selectively activate supraspinatus. While both EC and FC tests activated supraspinatus to levels approximately 90% MVC, eight other shoulder muscles tested including other rotator cuff muscles (infraspinatus and upper subscapularis), scapular positioning muscles (upper, middle and lower trapezius, and serratus anterior), and abduction torque producing muscles (anterior and middle deltoid) were activated to similarly high levels. In addition, supraspinatus and posterior deltoid were activated to similarly high levels in the EC test. As would be expected, for both EC and FC tests the prime movers for adduction (pectoralis major and latissimus dorsi) were only recruited at low levels (18–39% MVC). The stringent normalisation procedures15 and statistical analysis used in this study allow the conclusion that the EC and FC tests do not selectively activate supraspinatus. Therefore, the results of this study indicate that the EC and FC tests do not satisfy the stated criteria to be valid diagnostic tools for supraspinatus pathology, i.e. the EC and FC tests do not primarily activate supraspinatus with minimal activation from other shoulder muscles.6 The current study has demonstrated that the EC test highly activates anterior, middle and posterior deltoid, infraspinatus and serratus anterior as well as supraspinatus, and thus is broadly supported by the findings of previous EMG research.8,12,13 In addition, this study has demonstrated that the EC test activates the anterior rotator cuff (subscapularis) and another scapular positioning muscle (trapezius) to levels greater than 70% MVC, and except for posterior deltoid the EC and FC tests similarly activate all muscles tested. In examining the EC and FC tests for their ability to determine the presence of a tear in supraspinatus past researchers concluded that weakness should be used as an indicator of a positive test finding.22 However, it is clear from the results of the current paper that the EC and FC tests require high levels of activity in many muscles. Therefore, weakness in any of these muscles would affect the strength of the test and may then be interpreted as a positive test irrespective of whether a supraspinatus tear was present or not. For example, previous
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research23 has demonstrated that the position of the scapula can affect the strength of the EC test. Therefore, weakness in the scapular muscles, which could alter the optimal alignment of the scapula, could result in a positive test finding of supraspinatus pathology. As all scapular muscles tested in this study were recruited at high levels, weakness in any of these muscles is likely to have a major influence on the ability to generate force during the EC and FC tests. Similarly, our results indicate that all the rotator cuff muscles tested were activated at high levels during the EC and FC tests. As all the rotator cuff muscles are active during shoulder abduction24 weakness in any rotator cuff muscle could result in pain and weakness during these tests due to decreased dynamic support at the shoulder joint. Once again this could lead to a false positive interpretation of the EC and FC tests as indicating supraspinatus pathology. The results of the current study provide evidence to explain the poor specificity16–18 and accuracy19,20 demonstrated by both the EC and FC tests in diagnosing supraspinatus pathology. Clinical studies indicate that while these tests are likely to be positive if pathology in supraspinatus is present (high sensitivity) they will also be positive when pathologies exist in other structures (low specificity). Since many other shoulder muscles are highly activated during both these tests the presence of pathology in any of these muscles, or other joint structures influenced by these muscles, e.g. articular surface alignment, would contribute to the lack of specificity demonstrated by the EC and FC tests in these clinical studies. The EC and FC are often recommended as positions for strengthening supraspinatus.12,25,26 The results of the current study confirm that the EC and FC positions are effective in highly activating the supraspinatus and therefore, can be used for strengthening this muscle. However, this study also confirms that supraspinatus activation does not occur in isolation to other shoulder muscles during the EC and FC tests but in combination with them. The finding that many of the shoulder muscles, including other rotator cuff muscles, abduction torque producing muscles and the scapular positioning muscles are highly activated during these tests increases the potential use of the EC and FC test positions in shoulder exercise programs. As many muscles can be strengthened simultaneously, use of the EC and FC test positions may reduce the number of exercises required during a strengthening program. In addition, by activating muscles from each of the three main shoulder muscle groups, the EC and FC test positions may be useful in promoting the coordinated muscle activity necessary for normal asymptomatic shoulder function.27 Practical implications • EMG examination of muscle activation during the ‘empty can’ and ‘full can’ tests indicates that these tests do not selectively activate supraspinatus.
• The ‘empty can’ and ‘full can’ tests should not be interpreted as definitive tests of supraspinatus pathology. • Results showing many muscles are activated during these positions suggest they may be useful for strengthening many shoulder muscles simultaneously. Acknowledgments This project has received no financial support. The authors wish to thank the subjects for the time they volunteered to participate in this study. References 1. Ellman H. Diagnosis and treatment of incomplete rotator cuff tears. Clin Orthop 1990;(May (254)):64–74. 2. Gschwend N, Ivosevi-Radovanovi D, Patte D. Rotator cuff tear–relationship between clinical and anatomopathological findings. Arch Orthop Trauma Surg 1988;107(March (1)):7–15. 3. Neer II CS. Impingement lesions. Clin Orthop 1983;173(March):70–7. 4. Hertel R, Ballmer FT, Lambert SM, Gerber Ch. Lag signs in the diagnosis of rotator cuff rupture. J Shoulder Elbow Surg 1996;5(4 (July–August)):307–13. 5. Jobe FW, Moynes DR. Delineation of diagnostic criteria and a rehabilitation program for rotator cuff injuries. Am J Sports Med 1982;10(November–December (6)):336–9. 6. Kelly BT, Kadrmas WR, Speer KP. The manual muscle examination for rotator cuff strength: an electromyographic investigation. Am J Sports Med 1996;24(September–October (5)):581–8. 7. Blackburn Jr TA. Rehabilitation of the shoulder and elbow after arthroscopy. Clin Sports Med 1987;6(July (3)):587–606. 8. Townsend H, Jobe FW, Pink M, Perry J. Electromyographic analysis of the glenohumeral muscles during a baseball rehabilitation program. Am J Sports Med 1991;19(May–June (3)):264–72. 9. Brukner P, Khan K. Clinical sports medicine. 3rd ed. Sydney: The McGraw-Hill Companies, Inc.; 2007. 10. Donatelli RA. Physical therapy of the shoulder. 4th ed. St. Louis: Churchill Livingstone; 2004. 11. Ellenbecker TS. Clinical examination of the shoulder. St. Louis: Elsevier Saunders; 2004. 12. Malanga GA, Jenp YN, Growney ES, An K. EMG analysis of shoulder positioning in testing and strengthening the supraspinatus. Med Sci Sports Exerc 1996;28(June (6)):661–4. 13. Reinold MM, Macrina LC, Wilk KE, Fleisig GS, Dun S, Barrentine SW, et al. Electromyographic analysis of the supraspinatus and deltoid muscles during 3 common rehabilitation exercises. J Athlet Train 2007;42(October–December (4)): 464–9. 14. Rowlands LK, Wertsch JJ, Primack SJ, Spreitzer AM, Roberts MM. Kinesiology of the empty can test. Am J Phys Med Rehabil 1995;74(July–August (4)):302–4. 15. Boettcher C, Ginn KA, Cathers I. Standard maximum isometric voluntary contraction tests for normalizing shoulder muscle EMG. J Orthop Res 2008. Published online doi:10.1002/jor.20675. 16. Holtby R, Razmjou H. Validity of the supraspinatus test as a single clinical test in diagnosing patients with rotator cuff pathology. J Orthop Sports Phys Ther 2004;34(April (4)):194–200. 17. Itoi E, Minagawa H, Yamamoto N, Seki N, Abe H. Are pain location and physical examinations useful in locating a tear site of the rotator cuff? Am J Sports Med 2006;34(February (2)):256–64. 18. Leroux JL, Thomas E, Bonnel F, Blotman F. Diagnostic value of clinical tests for shoulder impingement syndrome. Rev Rhum (Engl Ed) 1995;62(June (6)):423–8.
C.E. Boettcher et al. / Journal of Science and Medicine in Sport 12 (2009) 435–439 19. Park HB, Yokota A, Gill HS, Rassi GE, McFarland EG. Diagnostic accuracy of clinical tests for the different degrees of subacromial impingement syndrome. J Bone Joint Surg Am 2005;87(July (7)):1446–55. 20. Kim EJH, Lee KW, Song JS. Interpreting positive signs of the supraspinatus test in screening for torn rotator cuff. Acta Med Okayama 2006;60(4):223–8. 21. Tennent TD, Beach WR, Meyers JF. A review of the special tests associated with shoulder examination. Part 1: The rotator cuff tests. Am J Sports Med 2003;31(1):154–60. 22. Itoi E, Kido T, Sano A, Urayama M, Sato K. Which is more useful, the “full can test” or the “empty can test” in detecting the torn supraspinatus tendon? Am J Sports Med 1999;27(January–February (1)):65–8. 23. Kibler WB, Sciascia A, Dome D. Evaluation of apparent and absolute supraspinatus strength in patients with shoulder injury using the
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scapular retraction test. Am J Sports Med 2006;34(October (10)): 1643–7. Sharkey NA, Marder RA, Hanson PB. The entire rotator cuff contributes to elevation of the arm. J Orthop Res 1994;12(September (5)):699–708. Burke WS, Vangsness CT, Powers CM. Strengthening the supraspinatus: a clinical and biomechanical review. Clin Orthop 2002;(September (402)):292–8. Takeda Y, Kashiwaguchi S, Endo K, Matsuura T, Sasa T. The most effective exercise for strengthening the supraspinatus muscle: evaluation by magnetic resonance imaging. Am J Sports Med 2002;30(May–June (3)):374–81. Ludewig PM, Borstead, John D. Upper extremity joint complexes. In: Levangie PK, Norkin C, editors. The shoulder complex in joint structure and function: a comprehensive analysis. Philadelphia: F.A. Davis Company; 2005. p. 233–71.
Journal of Science and Medicine in Sport 12 (2009) 435–439
Original paper
The ‘empty can’ and ‘full can’ tests do not selectively activate supraspinatus Craig E. Boettcher a,∗ , Karen A. Ginn a , Ian Cathers b a
Discipline of Biomedical Science, Faculty of Medicine, The University of Sydney, Australia b Faculty of Health Sciences, The University of Sydney, Australia
Received 26 June 2008; received in revised form 28 August 2008; accepted 1 September 2008
Abstract Based on previous electromyographic studies the ‘empty can’ (EC) and ‘full can’ (FC) tests have been promoted as being able to isolate activity to supraspinatus and are therefore diagnostic of supraspinatus dysfunction. However, there is evidence to suggest that these positions do not selectively activate supraspinatus, and that they may have poor diagnostic accuracy, bringing into question the validity of these tests. Due to limitations in the original EMG papers describing the EC and FC tests the current study aimed to further examine shoulder muscle activity during these tests to determine their ability to selectively activate supraspinatus. EMG activity was recorded from 13 muscles in 15 normal subjects while performing these two tests. Results showed that during the EC and FC muscle tests nine and eight other shoulder muscles, respectively, were equally highly activated as supraspinatus. It was concluded from these results that the EC and FC tests do not primarily activate supraspinatus with minimal activation from other shoulder muscles and therefore, do not satisfy basic criteria to be valid diagnostic tools for supraspinatus pathology. Therefore, these tests should not be interpreted as definitive tests for the clinical diagnosis of supraspinatus pathology. They may, however, be beneficial during shoulder muscle strengthening programs. © 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. Keywords: Shoulder; Supraspinatus; Empty can test; Full can test; Rotator cuff
1. Introduction Shoulder disorders are common and are often the result of rotator cuff tendinopathy, with the supraspinatus tendon most often affected.1–3 As a result clinical tests aimed at isolating activity in the supraspinatus musculotendinous unit to diagnose pathology4–6 and to strengthen the supraspinatus muscle7,8 have been developed. Jobe and Moynes (1982) first described a position of 90◦ arm abduction, 30◦ horizontal flexion, and full shoulder internal rotation, with resistance being applied to elevation, now known as the “empty can” (EC), “Jobe’s” or “supraspinatus” test (Fig. 1a). They claimed that with this test position the activity of the supraspinatus ‘can be isolated to some degree’5 . However, to support this conclusion, they reported only traces of raw EMG signal from all the rotator cuff muscles in only one subject and without further analysis. ∗
Corresponding author. E-mail address: [email protected] (C.E. Boettcher).
Further to this in 1996 Kelly et al. compared the EC test to a modification involving 45◦ external rotation instead of full internal rotation, termed the “full can” (FC) test (Fig. 1b). They found this position to activate the supraspinatus to a similar level to the EC test, but to activate the infraspinatus to a lesser degree. They also argued that the FC position would be less pain provoking than the EC test by avoiding the impingement position caused by the greater tuberosity rotating under the coraco-acromial arch during internal rotation, and thus would be a more reliable test of supraspinatus function. Although these researchers recorded from eight shoulder muscles they failed to report on the relative level of activity between the supraspinatus and muscles other than infraspinatus. Largely based on the results of these two studies the EC and FC tests have become commonly used clinical tests for diagnosing supraspinatus pathology. Current orthopedic physical assessment textbooks describe these tests as definitive for supraspinatus pathology9–11 —“the empty can test is a manual resistive test to assess the integrity of the
1440-2440/$ – see front matter © 2008 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jsams.2008.09.005
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in the clinical evaluation of supraspinatus pathology. Based on the premise that to be valid diagnostic tools to identify supraspinatus pathology, the EC and FC tests must be capable of primarily activating supraspinatus with minimal activation from other shoulder muscles,6 the aim of this study was to examine muscles from each of the major muscle groups of the shoulder during performance of the EC and FC tests to assess their ability to selectively activate supraspinatus.
2. Materials and methods
Fig. 1. Illustration of the “empty can” (EC) test (a) and “full can” (FC) test (b).
supraspinatus muscle-tendon unit”.11 However, the results of the EMG studies by Jobe et al. and Kelly et al. provide insufficient data to support the conclusion that the EC and/or FC tests isolate supraspinatus activity. Indeed, EMG evidence exists to suggest that the EC and/or FC tests highly activate deltoid,8,12,13 infraspinatus,12,14,15 subscapularis8,15 and serratus anterior12,15 as well as supraspinatus. In addition to the EMG evidence indicating that the EC and FC tests do not selectively activate supraspinatus, clinical studies raise doubt about the ability of these tests to determine supraspinatus pathology. Studies examining the diagnostic validity of the EC and FC tests using surgical and/or MRI findings to confirm supraspinatus pathology, indicate that they have poor to moderate specificity16–18 and accuracy.19,20 Tennent et al.21 makes the observation that many clinical tests lack an evidence base and have become, and remain, a part of the examination procedure through teaching without reference to the original descriptive papers. In light of weak EMG evidence to indicate that the EC and FC tests selectively activate supraspinatus, that other muscles are highly activated during these tests, and clinical studies questioning their validity as tests of supraspinatus pathology, it would seem that this may be the case for the EC and FC tests. Therefore, this comprehensive EMG study assessing shoulder muscle activation during the EC and FC tests was designed to determine the validity of the use of these tests
The data for the EC and FC tests examined in this paper are a subset of those from a previous study undertaken in our lab.15 Further details to those described here regarding experimental arrangements and procedures are provided in this earlier paper. Nine males and six females subjects with normal dominant shoulder function were recruited for this study (mean age 28.4 years, range 19–47 years). Testing was performed on normal subjects as it was determined that interpretation of the EC and FC tests in patients with shoulder pathology has to be based on an accurate understanding of normal muscle activation. This is in keeping with previous EMG studies examining these tests.5,6 The study was approved by The University of Sydney Human Research Ethics Committee and all subjects signed a University of Sydney approved informed consent form prior to participation. Electromyographic data were collected simultaneously from 12 shoulder muscles using a combination of surface and intramuscular fine-wire electrodes. Intramuscular electrodes were used to record activity from supraspinatus, infraspinatus, subscapularis, middle trapezius, lower trapezius, serratus anterior and latissimus dorsi. Surface electrodes were used for upper trapezius, anterior deltoid, middle deltoid, posterior deltoid and pectoralis major. Surface and intramuscular electrodes were attached to amplifiers (two Iso-DAM 8 amplifiers, World Precision Instruments). EMG signals were amplified (gain = 100) and filtered (HP = 10 Hz, LP = 1 kHz). Data was acquired on a personal computer with a 16 bit analog to digital converter (1401, Cambridge Electronics Design) at a sampling rate of 3571 Hz using Spike2 software (version 4.00, Cambridge Electronics Design) and stored for later off-line analysis. The test positions of abduction in the scapular plane (30◦ horizontal flexion) with internal rotation (EC position) and abduction in the scapular plane with external rotation (FC position) were examined in random order along with 13 other shoulder test positions as part of the larger study.15 Manual resistance was applied by one of the researchers at the wrist. Each contraction was held for 5 s with a gradual increase of resistance over 1 s, a sustained maximal contraction with resistance for 3 s, and a gradual release over the final second. Three repetitions of each test were performed, with a minimum rest interval of 30 s between each repetition. To ensure consistency of positioning during each isometric
C.E. Boettcher et al. / Journal of Science and Medicine in Sport 12 (2009) 435–439
test, subjects were closely monitored to ensure they did not attempt compensatory movements of the scapula or trunk. If it was determined that a test was being done incorrectly it was ceased and repeated. All raw EMG data was visually inspected and a confirmatory power spectral analysis performed when there was doubt regarding the validity of the signal from a channel. As a result of inspection 41 (3.5%) of the 1170 individual trials (15 subjects × 2 muscle tests × 13 muscle sites × 3 trials) were discarded due to movement artifact or a channel being lost during the experiment. These data were excluded from further analysis. The EMG signals were high pass filtered (20 Hz, 8th order Butterworth), rectified, and low pass filtered (3 Hz, 8th order Butterworth). The maximum value of the resulting EMG envelope was determined and this was averaged across the trials for each test. Values were normalised using the maximum activity level (MVC) generated for each muscle across the four isometric Shoulder Normalisation Tests recently validated to generate maximum activity in all muscles tested in this study.15 These tests were: abduction at 90◦ in full internal rotation, internal rotation at 90◦ abduction, flexion at 125◦ with scapula resistance, and horizontal adduction at 90◦ flexion. A two-way repeated measures ANOVA (with muscles and tests as factors) was undertaken (Statistica version 7.1, StatSoft). This was followed by Tukey post hoc tests. Statistical significance was accepted at a probability less than 0.05.
3. Results The mean activation levels (95% confidence levels) for the 13 shoulder muscle sites tested for both the EC and FC tests are illustrated in Fig. 2. Both tests activated supraspinatus and nine other muscle sites to above 70% of their maxima (Fig. 2).
Fig. 2. Activation levels for the 13 muscles in the “empty can” and “full can” tests. Bars indicate 95% confidence intervals.
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Results of the ANOVA indicated that there is very strong evidence of a difference in activation levels across all muscles (F(12,168) = 34.8; p < 0.001), with post hoc tests revealing that the mean activity in supraspinatus was only higher than that in latissimus dorsi, pectoralis major and lower subscapularis (p < 0.001), with no significant difference between levels of supraspinatus activity and the other muscles tested. While there was no evidence of a difference in the muscle activation levels between the EC and FC tests (F(1,14) = 2.10; p = 0.17), there was very strong evidence of a difference in muscle activation pattern in the two tests (F(12,168) = 3.33; p < 0.001) which post hoc testing revealed to be only for posterior deltoid (p < 0.05).
4. Discussion The results of this study have definitively determined that the EC and FC tests do not selectively activate supraspinatus. While both EC and FC tests activated supraspinatus to levels approximately 90% MVC, eight other shoulder muscles tested including other rotator cuff muscles (infraspinatus and upper subscapularis), scapular positioning muscles (upper, middle and lower trapezius, and serratus anterior), and abduction torque producing muscles (anterior and middle deltoid) were activated to similarly high levels. In addition, supraspinatus and posterior deltoid were activated to similarly high levels in the EC test. As would be expected, for both EC and FC tests the prime movers for adduction (pectoralis major and latissimus dorsi) were only recruited at low levels (18–39% MVC). The stringent normalisation procedures15 and statistical analysis used in this study allow the conclusion that the EC and FC tests do not selectively activate supraspinatus. Therefore, the results of this study indicate that the EC and FC tests do not satisfy the stated criteria to be valid diagnostic tools for supraspinatus pathology, i.e. the EC and FC tests do not primarily activate supraspinatus with minimal activation from other shoulder muscles.6 The current study has demonstrated that the EC test highly activates anterior, middle and posterior deltoid, infraspinatus and serratus anterior as well as supraspinatus, and thus is broadly supported by the findings of previous EMG research.8,12,13 In addition, this study has demonstrated that the EC test activates the anterior rotator cuff (subscapularis) and another scapular positioning muscle (trapezius) to levels greater than 70% MVC, and except for posterior deltoid the EC and FC tests similarly activate all muscles tested. In examining the EC and FC tests for their ability to determine the presence of a tear in supraspinatus past researchers concluded that weakness should be used as an indicator of a positive test finding.22 However, it is clear from the results of the current paper that the EC and FC tests require high levels of activity in many muscles. Therefore, weakness in any of these muscles would affect the strength of the test and may then be interpreted as a positive test irrespective of whether a supraspinatus tear was present or not. For example, previous
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research23 has demonstrated that the position of the scapula can affect the strength of the EC test. Therefore, weakness in the scapular muscles, which could alter the optimal alignment of the scapula, could result in a positive test finding of supraspinatus pathology. As all scapular muscles tested in this study were recruited at high levels, weakness in any of these muscles is likely to have a major influence on the ability to generate force during the EC and FC tests. Similarly, our results indicate that all the rotator cuff muscles tested were activated at high levels during the EC and FC tests. As all the rotator cuff muscles are active during shoulder abduction24 weakness in any rotator cuff muscle could result in pain and weakness during these tests due to decreased dynamic support at the shoulder joint. Once again this could lead to a false positive interpretation of the EC and FC tests as indicating supraspinatus pathology. The results of the current study provide evidence to explain the poor specificity16–18 and accuracy19,20 demonstrated by both the EC and FC tests in diagnosing supraspinatus pathology. Clinical studies indicate that while these tests are likely to be positive if pathology in supraspinatus is present (high sensitivity) they will also be positive when pathologies exist in other structures (low specificity). Since many other shoulder muscles are highly activated during both these tests the presence of pathology in any of these muscles, or other joint structures influenced by these muscles, e.g. articular surface alignment, would contribute to the lack of specificity demonstrated by the EC and FC tests in these clinical studies. The EC and FC are often recommended as positions for strengthening supraspinatus.12,25,26 The results of the current study confirm that the EC and FC positions are effective in highly activating the supraspinatus and therefore, can be used for strengthening this muscle. However, this study also confirms that supraspinatus activation does not occur in isolation to other shoulder muscles during the EC and FC tests but in combination with them. The finding that many of the shoulder muscles, including other rotator cuff muscles, abduction torque producing muscles and the scapular positioning muscles are highly activated during these tests increases the potential use of the EC and FC test positions in shoulder exercise programs. As many muscles can be strengthened simultaneously, use of the EC and FC test positions may reduce the number of exercises required during a strengthening program. In addition, by activating muscles from each of the three main shoulder muscle groups, the EC and FC test positions may be useful in promoting the coordinated muscle activity necessary for normal asymptomatic shoulder function.27 Practical implications • EMG examination of muscle activation during the ‘empty can’ and ‘full can’ tests indicates that these tests do not selectively activate supraspinatus.
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