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The reproducibility of assessing arm elevation in the scapular plane on the Cybex 340 Chris J. Duralla,b,c,∗,1 , George J. Davies b,c, Thomas W. Kernozek b, Mark H. Gibsona,d , Dennis C.W. Fatera,b and J. Scott Strakerb,c a
Gundersen-Lutheran Medical Center, LaCrosse, WI, USA b Physical Therapy Program, University of Wisconsin-LaCrosse, LaCrosse, WI, USA c Clinical and Research Services, Gundersen-Lutheran Sports Medicine, LaCrosse, WI, USA d Department of Sport and Exercise Science, Athletic Training Program, University of Wisconsin-LaCrosse, LaCrosse, WI, USA Isokinetic testing of arm elevation in the scapular plane offers several advantages over the frontal plane. The purpose of this investigation was to determine the intraexaminer reproducibility of scapular plane (30◦ anterior to frontal plane) elevation peak torques using a Cybex 340 isokinetic dynamometer. Twelve female and three male (N = 15) noninjured college students were tested on three separate occasions over a six week interval. Dominant shoulder scapular plane elevation was measured with participants seated utilizing a modified abduction/adduction protocol. Testing consisted of four gradient sub-maximum to maximum warm-ups followed by five maximum repetitions at 60◦ /sec, 180◦ /sec, and 300◦ /sec. Intraclass correlation coefficients (ICCs) indicated that scapular plane elevation peak torques may be measured using these techniques with good reproducibility at 60◦ /sec (0.870) and 180◦ /sec (0.827), and fair reproducibility at 300◦ /sec (0.708). Results suggest that scapular plane arm elevation isokinetic testing should be conducted at slower angular-velocities to obtain more reproducible measurements. Keywords: Isokinetic, scapular plane elevation, reproducibility
∗ Corresponding author: Chris Durall, Graduate Physical Therapy Program, University of Wisconsin-LaCrosse, 2036 Cowley Hall, LaCrosse, WI 54601, USA. Tel.: +1 608 785 8470; E-mail:
[email protected]. 1 This author was a graduate student in Physical Therapy Program at the University of Wisconsin-LaCrosse at the time this study was conducted.
Isokinetics and Exercise Science 8 (2000) 7–11 ISSN 0959-3020 / $8.00 2000, IOS Press. All rights reserved
1. Introduction In medical testing and scientific investigations, isokinetic devices have greatly added to the understanding of dynamic muscle function with their capacity to measure torque through a range of motion at various angular-velocities [4,10,15]. The isokinetic assessment of torque production during arm elevation is often performed with the arm in the coronal plane [26, 28]. Several investigators [4,7,8,13,15,16,27], however, have recommended isokinetic testing arm elevation in the scapular plane. There is a lack of consensus within the literature on the location of the scapular plane with a range of 30 ◦ to 45◦ anterior to the coronal plane being reported [4,5,7,8,15,16,27]. Cited benefits of testing and exercising in the scapular plane include (1) maximal congruency between the humeral head and glenoid [14,17,20,22], (2) optimal length-tension relationships of the humeral abductors and rotators [7,20], (3) approximation of a functional movement plane for many activities [4], (4) decreased stress on the anterior glenohumeral capsule [20], and (5) greater patient comfort during testing [14,15]. In addition, greater peak torques have been reported during arm elevation in the scapular plane compared to the coronal plane [25]. The validity of using isokinetic devices to provide objective data on dynamic muscle function has been well established [4,10,15]. Some isokinetic testing procedures, however, lack evidence of reproducibility. The reproducibility of the Cybex 340 isokinetic dynamometer (Lumex, Inc., Ronkonkoma, NY) has been reported previously for measurements of shoulder elevation in the coronal plane [26], however, the reproducibility of testing arm elevation in the scapular plane on a Cybex 340 has not been reported. 1.1. Purpose The objective of this investigation was to determine the intra-examiner reproducibility of peak torque measurements of arm elevation in the scapular plane on the Cybex 340. Measurements were taken during three
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C.J. Durall et al. / The reproducibility of assessing arm elevation in the scapular plane on the Cybex 340 Table 1 Participant characteristics (mean ± SD) Females Males
N 12 3
Age (yr) 22.75 ± 2.25 21.33 ± 0.58
Height (cm) 137.3 ± 22.3 164.0 ± 23.3
Weight (kg) 64.1 ± 4.02 69.3 ± 2.52
testing sessions over a six-week interval to study the consistency of measurements over time. With reference to the glenohumeral joint, scapular plane elevation is operationally defined as the elevation of the arm in the scapular plane, 30 ◦ anterior to the coronal plane [8, 14].
2. Methods 2.1. Participants A convenient sample of 12 female (20–29 years of age, mean age 23.6 years) and three male (21–26 years of age, mean age 22.5 years) noninjured students at the University of Wisconsin-La Crosse participated in this study (Table 1). Prior to testing, each volunteer completed a questionnaire regarding present and past shoulder, elbow, and wrist/hand pathology; those with a history of injury were screened by the same licensed Physical Therapist. Screening consisted of shoulder and upper extremity range of motion, manual muscle testing as outlined by Daniels and Worthingham [3], and shoulder impingement testing as described by Hawkins and Kennedy [11] and Neer and Welch [19]. Exclusion criteria consisted of shoulder or upper extremity pain during screening or insufficient range of motion to perform the testing procedures. Following screening, testing procedures were explained. Each participant signed an informed consent form approved by the Institutional Review Board at the University of WisconsinLa Crosse. All participants agreed not to alter their current activity level or training program during their involvement in the study. 2.2. Testing procedure A calibrated Cybex 340 (Lumex Corp.,Ronkonkoma, NY) computerized isokinetic dynamometer was used to measure peak torque produced during scapular plane elevation. One investigator conducted each isokinetic testing session. Prior to data collection, participants performed a submaximal upper extremity warm-up for five minutes (2.5 minutes forward and 2.5 minutes reverse) on a Cybex Fitron (Lumex, Inc., Ronkonkoma, NY) modified for upper extremity exer-
cise at a metronome-guided cadence of 60 revolutions per minute. Similar warm-up protocols have been reported in related studies [6,9,12]. All testing was performed on the dominant arm as determined by throwing preference. Scapular plane elevation was tested with the participant seated and stabilized on the fully upright Upper-Body Exercise and Testing Table (UBXT) (CyR bex, Inc., Ronkonkoma, NY). Four-inch-wide Velcro straps were placed horizontally around the upper chest (through the axilla) and around the waist to minimize extraneous trunk movement. The dynamometer head was tilted 40◦ upward (equivalent to the UBXT backrest angle) and then raised or lowered until the input shaft of the dynamometer bisected the participant’s glenohumeral joint axis of rotation. The UBXT was positioned 60◦ from the coronal plane relative to the dynamometer head (Fig. 1). Tape was adhered to the floor to mark this angle to aid in alignment of each subject. Modifying the UBXT position in this manner allowed arm elevation to occur in the plane of the scapula 30 ◦ anterior to the coronal plane. The scapular plane angle was verified prior to each test by the same examiner using a standard hand-held 360 ◦ goniometer marked in 1◦ increments. A mechanical stop was set on the dynamometer to limit scapular plane elevation to 150 ◦ for each participant as described by Whitcomb et al. [28]. The safety cushion on the UBXT was used as a mechanical stop during arm adduction. Prior to each test, the participant’s arm and dynamometer attachment were weighed following the Cybex 340 protocol to eliminate the effect of gravity. To minimize the risk of subacromial impingement as described by Hawkins and Kennedy [11], participants used a rotating handgrip on the shoulder-testing accessory and long-input adapter attachment and were instructed to “lead with the thumb” during scapular plane elevation. The non-testing hand gripped an offset handle attached to the UBXT during testing. Dynamometer position, mechanical stop positions, and attachment settings were carefully recorded for each participant to ensure replication during subsequent testing. The testing protocol consisted of four gradient submaximal to maximal isokinetic warm-ups followed by five maximal effort test repetitions at angular velocities of 60◦ /sec, 180◦ /sec, and 300 ◦ /sec. Participants were given consistent verbal encouragement during each test repetition but no visual feedback of torque output. Using the pre-test settings, each participant was re-tested at three weeks and six weeks following pre-testing. These testing intervals were chosen to reflect typical clinical testing intervals.
C.J. Durall et al. / The reproducibility of assessing arm elevation in the scapular plane on the Cybex 340
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Fig. 1. Isokinetic testing position for scapular plane elevation on the Cybex 340. Table 2 Pre-test and Post-test mean (± SD) peak torques at three angularvelocity test conditions for female participants (N = 12) Angular-velocity 60◦ /sec 180◦ /sec 300◦ /sec
Peak torque mean ± SD (Nm) Pre-test Post-test 1 Post-test 2 23.75 ± 4.07 23.67 ± 2.84 24.17 ± 3.86 22.67 ± 4.61 21.42 ± 4.87 23.08 ± 4.27 16.00 ± 5.06 14.58 ± 5.23 17.92 ± 6.50
2.3. Data analysis R R for Windows (Version 8.0, SPSS, Inc., SPSS Chicago, IL) software was used to perform the statistical analysis. ICCs were calculated as described by Shrout and Fleiss [24] to determine the test-retest reproducibility of the peak torque measurements at each angular-velocity tested.
3. Results All 15 participants completed the required 3 testing sessions over the six-week interval (compliance = 100%). Reproducibility of peak torques generated during scapular plane elevation were ICC = 0.870 at 60◦ /sec, ICC = 0.826 at 180 ◦ /sec, and ICC = 0.708 at 300◦ /sec. Although no universally accepted ICC values have been established, Currier [2] reported that
coefficients between 0.90 to 0.99 indicate “high” reproducibility, 0.80 to 0.89 “good” reproducibility, 0.70 to 0.79 “fair” reproducibility, and 0.69 “poor” reproducibility. Based on this criteria, the coefficients values in the present investigation indicate good reproducibility at 60 ◦ /sec and 180◦ /sec, and fair reproducibility at 300 ◦ /sec. Lower reproducibility coefficients were found at higher angular velocities, demonstrating an inverse relationship between reproducibility and angular-velocity (Fig. 2).
4. Discussion The ICC indicates the dependability, repeatability, or reproducibility of the measuring instrument and describes the consistency with which an individual maintains his position within a group when the measurement procedure is repeated [2,21,24]. The calculated coefficient is interpreted as the variability between and within measurements. The closeness of the measurements indicates the dependability of the procedure. Ideally, the measurement should remain constant across time, reflected in a higher coefficient close to 1. The ICCs obtained from repeated testing during scapular plane elevation are similar to the values reported by Kuhlman et al. [15]. They reported ICCs
C.J. Durall et al. / The reproducibility of assessing arm elevation in the scapular plane on the Cybex 340
Correlation Coefficients
10
0.9 0.85 0.8
ICCs
0.75 0.7 60
180
300
Angular Velocity r(degrees pe sec) Fig. 2. Intraclass correlation coefficients at three angular-velocity test conditions.
of 0.88 at 90 ◦ /sec and 0.76 at 210 ◦ /sec with repeated testing of scapular plane elevation on a Lido 2.0 (Loredan Biomedical, Davis, CA) isokinetic dynamometer. Mayer et al. [18] reported a 15% variability in the reproducibility of peak torque measurements for concentric isokinetic shoulder abduction at 60 ◦ /sec in non-injured subjects. The scapular plane elevation peak torque values of the female participants in this study (Table 2) are similar to those reported by Cahalan et al. [1]. They tested dominant shoulder scapular plane elevation (defined as elevation 30 ◦ anterior to the coronal plane) in a group of non-injured subjects. Mean peak torque values of female participants at 60 ◦ /sec, 180◦ /sec, and 300 ◦ /sec were 27.2, 17.7, 10.9 Nm respectively. Although the sample in the present study was comprised of both males and females, the majority of participants were female. The observed trend of declining reproducibility as isokinetic angular-velocity increased has been reported by other investigators as well [15,18,26]. This trend may be due to problems with torque overshoot [23]. As the pre-set angular-velocity increases, greater freelimb acceleration must be generated to reach the preset angular-velocity. When limb acceleration exceeds the pre-set angular-velocity,the dynamometer feedback mechanism is activated and a resistive torque is applied by the dynamometer to decelerate the limb to the pre-set angular-velocity. When this occurs, the torque generated by the dynamometer to decelerate the limb produces an “overshoot” in measured torque [23]. During isokinetic testing, torque overshoot may be interpreted as actual peak torque values rather than an artifact associated with the instrumentation. Because more free-limb acceleration occurs at higher pre-set angular velocities, torque overshoot and peak torque variabil-
ity may increase. Other sources of variability include subject fatigue, experience in using the apparatus, subject positioning, time of day (which may affect circadian rhythms), and testing-room conditions. Although steps were taken to standardize subject positioning and testing-room conditions, there is no possible way to eliminate all of these sources of variability. There are several limitations to the present study including (1) a small sample size, precluding extrapolation to a large population; (2) a disproportionate ratio of male and female participants, also precluding extrapolation to a large population; and (3) a sample of uninjured participants, precluding extrapolation to patients with glenohumeral dysfunction. Results of this investigation suggest that isokinetic assessment of arm elevation in the scapular plane should be conducted at slower angular-velocities (e.g. 60 ◦ /sec, 120◦/sec, 180◦ /sec) to obtain more reproducible measurements.
Acknowledgements Gratitude is owed to Dan Dahle, Shawn Rankin, and Jennifer Smader for their assistance with data collection.
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