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Technical Reports |
SP O'Leary, MPhty(Manip), BPhty(Hons), is a doctoral student at The University of Queensland
BT Vicenzino, PhD, MSc, GradDipPhty(Sports), BPhty, is Senior Lecturer, Division of Physiotherapy, The University of Queensland
GA Jull, PhD, MPhty, GradDipAdvManipTher, is Professor and Head, Division of Physiotherapy, The University of Queensland
Address all correspondence to Mr O'Leary at Department of Physiotherapy, The University of Queensland, Brisbane, Queensland, 4072 Australia (s.oleary{at}shrs.uq.edu.au)
Submitted February 23, 2004;
Accepted November 19, 2004
 | Abstract |
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Key Words: Craniocervical flexor muscles • Isometric dynamometry
| Introduction |
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 TopAbstract Introduction MethodResultsDiscussionConclusionReferences |
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Because of their specific function, there has been a trend in research and in clinical practice to evaluate the CC flexor muscles separately from the cervicothoracic flexors.10–17 When compared with subjects with no history of neck pain, subjects with idiopathic11,13,16 and traumatic onset14,17 neck disorders have shown deficits in the contractile capacity of their CC flexor muscles. These deficits include reductions in maximal voluntary isometric contractions (MVIC)16 and decreases in the capacity to sustain maximal16 and submaximal13,14,17 CC flexion contractions. However, there currently are no clinical procedures for measuring the performance of the CC flexor muscles over a range of contraction intensities. We believe that conventional cervical flexion dynamometry methods,18,19 which resist muscle forces at the forehead, may not isolate contraction of the CC flexor muscles specifically enough to adequately assess their performance.
Watson and Trott16 described a dynamometry method used with the person being tested in the supine position that specifically assesses CC flexor muscle performance. This method measured the force the CC flexor muscles could exert on a force-sensitive metal bar positioned on the undersurface of the mandible. A pressure sensor, placed under the supporting surface of the head, simultaneously monitored changes in the head pressure on the supporting surface to ensure an isolated CC flexion action. Using this method, Watson and Trott16 demonstrated intraexaminer reliability (Pearson correlation coefficient [r]=.93) and found reductions in the MVIC of the CC flexor muscles in patients diagnosed with cervicogenic headache compared with subjects with no history of neck pain. As Mayhew and Rothstein20 pointed out, however, the measurement of muscle force can be problematic because it depends on the distance that the resistance is from the axis of rotation (AOR) of the muscles. Force measurements may vary considerably unless the device is applied at the exact anatomical position for each test, even if muscle tension is identical. Consequently, it may be difficult to compare measurements of force at different points within individuals or at the same point between individuals, and this difficulty compromises the method's potential to be used for dynamic through-range muscle tests in the future.
The purpose of this technical report is to describe a new dynamometry method designed to measure the torque-generating capacity of the CC flexor muscles about the AOR of cranium-C1, with the intent of ascertaining their performance. Muscle forces exert torque to the skeletal system about articular axes. Isometric dynamometry measures torque exerted by muscle groups on the static skeleton in a single plane. In complex multisegmental regions, such as the cervical spine, the torque-generating capacity of planar muscle groups can be simplified by resolving all moments to a single point.18,19,21 Several researchers have used this method for the cervical flexor muscles by resisting forces at the forehead and resolving moments to the cervicothoracic junction (C7–T1),18 the C7 vertebra,19 or the level of the C4 vertebra.21 These methods refer to isometric tests of cervical flexor muscle performance that, if unrestrained, would produce flexion of the head and cervical spine together on the thorax (cervicothoracic flexors), as is the case with conventional cervical flexion dynamometry. The method of isometric dynamometry described in this technical report resists forces at the undersurface of the mandible that, if unrestrained, would produce flexion of the head on the cervical spine (CC flexors), while resolving all moments to the 0/C1 motion segment, the principal articulation of CC flexion. We believe that this is the most appropriate method to physically measure the contractile performance of the CC flexor muscles and that it has potential to be used in the future as a clinical measure of these important muscles.
This article is in 2 parts: the first part describes the specifications of the device and calibration procedure, and the second part discusses the reliability of the measurements obtained during the CC flexor muscle performance tests. Muscle performance tests include the measurement of CC flexor muscle MVIC at 3 different points in the CC flexion range and measurement of the steadiness of a sustained isometric contraction (standard deviation of the sustained torque amplitude) at low (20% MVIC) and moderate (50% MVIC) intensities of contraction in the middle neutral position of the CC flexion range. Maximal voluntary isometric contraction of this muscle group has previously been investigated,16 as have tests of sustained submaximal contractions.13,14,17 We believe the muscle performance tests, performed as described in this article and using this new technology, may reflect aspects of daily CC flexor muscle function and, therefore, are potential clinical tests of their performance.
| Method |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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A subject's CC flexion effort was resisted at the inferior border of the mandible by the application pad of the dynamometer. The force that the mandible exerted on the application pad was transferred by way of the lever arm, producing torque at the dynamometer axis, which was locked to the load cell deflection arm of the dynamometer. This torque, via the load cell deflection arm, deflected one end of a thin-beam load cell (TBS Series
), causing a change in voltage across the load cell. The voltage change was amplified (PM4-SG-240-5E-A
) and transmitted to a personal computer equiped with a custom-written LabVIEW (LabVIEW 6i Virtual Instruments
) program calibrated to convert the amplified voltage to the corresponding torque measurement (in newton-meters). The data were recorded and displayed in real time at a rate of 20 Hz. In addition, the dynamometer axis was adjustable so that it could be freely rotated to the appropriate point in the CC flexion range and then locked to the load cell deflection arm, allowing torque to be measured at the inner, middle, and outer positions of CC flexion range. The LabVIEW software was programmed to zero the torque measurement with the subject completely relaxed immediately prior to applying force to the dynamometer application pad to negate the effects of gravity on the lever arm at different positions relative to the horizontal. The measurement of torque exerted by a subject to the dynamometer axis then could be measured accurately.
Dorsal head force measurement.
A secondary feature of the device was a force-sensitive supporting surface for the head included to monitor extraneous motion of the head during the performance of the craniocervical flexor muscle test. Changes in dorsal force on the supporting surface by the head resulting from flexion (a reduction in force) or extension (an increase in force) of the head and neck together in the sagittal plane were measured by a second load cell (ESP Series) attached under the head platform of the dynamometer. The head platform was secured to one end of the load cell, and the other end of the load cell was secured to the bench. The dorsal force that the head exerted on the head platform deflected one end of the load cell, causing a change in the voltage across the load cell that was amplified and converted to the appropriate force (in newtons). In addition, the supporting surface of the head platform was positioned on ball bearings to allow CC flexion effort with minimal frictional effects at the head-platform interface.
Calibration and linearity of the instrument.
Amplified voltage outputs of the instrument were recorded for known torque increments at the dynamometer axis, which was achieved by positioning calibrated weights on the horizontal dynamometer resistance arm at staged distances from the axis. Mass ranging from 0.5 to 15 kg was used over lever arm distances of 75 to 135 mm. These parameters adequately covered the range of the lever arm length or force variables observed in pilot trials. The relationship between voltage output recordings and torque increments was modeled by linear regression to determine the least squares regression equation for the voltage data. The LabVIEW program used this equation to convert the amplified voltage to the appropriate torque measurements. The accuracy and linearity of the dynamometer–computer software instrument to measure static torque was then tested by reapplying the weights at various lever arm lengths. The relationship between the recorded torque and the expected torque was modeled by linear regression. The measurement system demonstrated linearity (R>.99) with an offset of –0.072 N·m.
Part 2: Test-Retest Reliability Study
Subjects.
Twenty subjects (15 women, 5 men) participated in the study. Subjects were recruited by printed and electronic advertising within the university. The subjects' mean age was 27.9 years (range=18–47 years), and they were 12 subjects with neck pain and a control group of 8 subjects with no history of neck pain. Subjects with and without neck pain were included because the intended use of the technology is to compare CC flexor muscle performance between these groups in future studies, and thus the reliability of data obtained with the method in both subject groups warrants investigation. Subjects in the neck pain group were included if they currently had neck pain of greater then 3 months' duration; scored 10 or greater (out of a possible total score of 100) on the Neck Disability Index (average=20.4, range=10–46), indicative of at least mild neck pain and disability25; and demonstrated signs of cervical spine dysfunction on a physical examination of the neck (abnormal cervical motion, abnormal resistance, and pain provocation to palpation of cervical motion segments).26 Subjects in the control group were included if they reported no history of neck pain, scored less than 10 on the Neck Disability Index (average=3.5, range=0–8), and had no signs of cervical spine dysfunction on a physical examination of the neck. Volunteers were not considered if they demonstrated neck pain from nonmusculoskeletal causes, neurological signs, any medical disorder that contraindicated physical exercise, or a history of surgery to the cervical spine. After receiving verbal and written information, each subject signed a consent form. This study was granted ethical clearance by the Institute Review Board of The University of Queensland.
Experimental procedure.
A test-retest design was used. All 20 subjects were tested on 2 separate occasions spaced 2 weeks apart to minimize training or fatigue effects between sessions. In each session, MVIC recordings were made in the inner, middle, and outer ranges of CC flexion. Sustained submaximal test recordings (20% and 50% of MVIC) were made in the middle range (craniocervical neutral position) only. The MVIC recordings were always completed first, and the order of testing was randomized among subjects but was consistent within subjects and between sessions. The same investigator (SOL) conducted all measurement sessions.
All tests were performed with the subject in a supine position. To minimize the effects of limb movements on CC flexor muscle performance, the subject's legs were suspended on slings so that the knees and the hips were flexed to 45 degrees and the arms were folded across the chest. Soft straps were attached to the supporting surface and were secured lightly over the subject's shoulders to avoid movement of the trunk on the supporting surface. The subject's AOR landmark (concha of the ear) and the dynamometer axis were aligned with the head in a neutral CC flexion/extension position according to a standard anthropometric neutral position of the head (Frankfort plane).27 In this craniocervical position, with the subject positioned supine, a vertical line bisects the orbitale and the tragion anatomical landmarks to position the craniocervical spine in a neutral flexion/extension position.27 The dynamometer-subject axes were aligned with the aid of a Web camera (QuickCam Pro 4000||) erected perpendicular to the axis of the dynamometer (Figure). Custom-written software (Visual Basic 6.0#) permitted the location of anatomical landmarks on the head (AOR landmark and nostril) and dynamometer reference points (dynamometer axis and lever arm) to be recorded from the Web camera image and replicated on subsequent sessions.
Once the dynamometer lever arm was fitted in a CC spine-neutral position, the location of the anatomical and dynamometer reference points was recorded as the position for isometric torque measurements in the middle CC flexion range. For inner-range measurements, the subject's head and lever arm was positioned in 10 degrees of head flexion from the neutral position. For outer-range measurements, the subject's head and lever arm was positioned in 10 degrees of head extension from the neutral position. The location of the anatomical and lever arm reference points were recorded for each of the 3 positions in the CC flexion range. Ten degrees to either side of the neutral CC position was chosen to represent inner and outer CC flexion ranges, based on reported cranium-C1 extension-to-flexion ranges of motion in the vicinity of 20 degrees (18.63°±1.51°).1
A visual display unit was then set up in the subject's view. When the subject performed a CC flexion effort against the dynamometer resistance arm, a visual feedback graph was displayed on the screen, increasing or decreasing in accordance with torque production. To avoid bias of performance, the visual feedback graph had no visible units or markings of scale so that, for MVIC tests, subjects were unable to grade the distance the graph moved up the screen visually either between repetitions or between measurement sessions. For sustained submaximal tests (20% and 50% MVIC), visual indicators were displayed on the visual display unit so that the subjects knew how intensely they had to perform a CC flexor contraction to achieve contraction intensities of 20% and 50% of their peak MVIC effort.
All subjects were given standard instructions, familiarization of the testing procedure, and a standard warm-up in all 3 ranges immediately before the trial in that range. Subjects were instructed to nod their head so that their mandible pushed downward on the application pad of the dynamometer to elevate the visual display column maximally. They practiced performing the task, ensuring that the head remained in contact with the head platform and that the teeth remained occluded to minimize the potential contribution of the mandibular depressors. Warm-up consisted of 4 submaximal repetitions, with each successive repetition at a greater intensity than the previous one, and a fifth repetition to their maximal ability. Three MVIC trials then were performed, with 60 seconds of rest between maximal efforts. Each contraction lasted between 3 and 5 seconds. Subjects were instructed to completely relax between repetitions, ensuring that no active force was placed on the application pad of the dynamometer until commencement of the next trial. The peak of the 3 MVIC trials was recorded as the MVIC score for the range for the session. In addition, the corresponding change in dorsal head force (force at peak torque – force at rest) was recorded. This was done to determine whether the measurements of isometric CC flexor muscle torque and dorsal head force at the moment of peak torque could be recorded consistently in order that the relationship between the 2 measures could be observed and questions about the possible need to control the dorsal head force variable could then be raised and investigated in future studies. This was repeated in all 3 ranges (inner, middle, and outer), with 5 minutes of rest between ranges.
A further 5 minutes of rest was given before subjects performed sustained CC flexor muscle contractions in the middle range position at 20% and 50% of the middle-range MVIC score. First, the contraction at 20% of MVIC was sustained for 65 seconds. Two minutes of rest was given before the subject sustained the 50% of MVIC for 35 seconds. The subject was allowed 5 seconds to reach the requested isometric CC flexor torque amplitude in both sustained tests. Data for this initial 5-second period were discarded; therefore, data from the sustained tests at 20% and 50% of MVIC were analyzed for a 60-second period and a 30-second period, respectively.
For all tests, subjects were blinded to the measurement of dorsal head force. Instead, the focus of the subject was on production of CC flexion torque with visual and standardized verbal encouragement given.
Data management and statistical analysis.
For the MVIC tests, means and 95% confidence intervals for both testing sessions (days 1 and 2) were calculated for CC flexor peak torque and corresponding change in dorsal head force in each range for both the neck pain group and the control group. The steadiness of the contraction was measured by computing the standard deviation of the torque amplitude for the 60-second and 30-second contraction periods for the sustained tests of 20% and 50% of MVIC, respectively. Corresponding dorsal head force data were transformed to a change value (in newtons) by calculating the difference between the dorsal head force measurement at rest immediately before commencing the test and the dorsal head force measurement recorded over the first and final 5-second periods of the sustained tests. Means and 95% confidence intervals for both standard deviation and dorsal head force data were calculated for both measurement sessions for the neck pain group, and the control group. Reliability for all measures was expressed for the neck pain and control groups separately by intraclass correlation coefficients (ICC, df=2,1) and standard error of the measurement (SEM) indexes.
| Results |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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| Discussion |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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The results of this study demonstrated that this new method has good reliability in the measurement of MVIC peak torque (ICC=.79–.93) with a relatively small SEM (0.6–1.4 N·m) and minimal disparities in reliability coefficients calculated for the neck pain and control groups (Tab. 2). These reliability coefficients are similar to those found by Watson and Trott16 in their measurement of MVIC force of the CC flexor muscles (r=.93); however, unlike our experiment, they ensured that the dorsal head forces remained steady during CC flexor force measurements. Because we wanted to determine the spontaneous dorsal head force response in this preliminary study, dorsal head force was not controlled in our study and subjects were blinded to this measure. A consistent finding across all tests was one of substantial increases in dorsal head force of 154% to 180% during MVIC tests compared with resting dorsal head force and of 38% and 97% during the final 5-second period of the sustained 20% and 50% MVIC tests, respectively. This increase in dorsal head force may be a strategy to improve the neuromuscular efficiency of the CC flexor muscles to gain maximal torque and to sustain torque over time.
In our preliminary investigation, this strategy would appear to be an inconsistent response during MVIC tests and a consistent response during sustained submaximal tests. Change in dorsal head force at peak torque demonstrated large disparities between the reliability coefficients of the neck pain group (ICC=.09–.87) and the control group (ICC=.49–.96) as well as large measurement error (Tab. 2). Very poor consistency of the dorsal head force measurement was noted for the control group in the inner range and for the neck pain group in the outer range. During the sustained 20% and 50% of MVIC tests, dorsal head force measurements at the initial 5-second period (ICC=.80–.90) and the final 5-second period (ICC=.77–.91) both had sound test-retest reliability for both groups. In future studies using this new method to compare CC flexor muscle performance, we will investigate, in large cohorts of subjects with and without neck pain, whether dorsal head force needs to be controlled (as well as the degree of control) to avoid compromising the sensitivity of the CC flexor torque measurement in detecting muscle impairment. We are cautious about adding the control of dorsal head force to the method, because we expect that it will add complexity to the test and may compromise its potential clinical application.
The reliability of data for a measure of contraction steadiness during sustained submaximal CC flexor muscle tests also was assessed by computing the standard deviation of the torque amplitude over the test periods. This measurement may reflect the capacity of the CC flexor muscle group to sustain the torque that may be required in prolonged postural tasks. The measurement showed sound reliability for the 20% of MVIC test (ICC=.74–.80), but large disparities were found between the neck pain group (ICC=.76) and the control group (ICC=.07) for the 50% of MVIC test, with the control group demonstrating very poor reliability coefficients. Again, the implications of not controlling dorsal head force during these tests are unknown at this stage.
We included subjects with and without a history of neck pain in the study because in subsequent studies we will compare muscle performance between these groups and it has been suggested that reliability studies should be performed on population groups of concern.28 The dynamometer data appeared to be equally reliable for both subject groups, indicating that meaningful comparisons of CC flexor muscle performance can be made in future studies between subjects with neck pain and control subjects. Meaningful group comparisons, however, cannot be made regarding CC flexor muscle performance from this data set because the groups were not matched for age, weight, or sex. This device appears to have application in the evaluation of neck pain and neck muscle impairment.
The technology described in this report is currently a research tool and is not commercially available for clinical application. Subject to device modifications, the technology has the potential to be used for both CC flexion and extension muscle performance, giving it considerable value for future clinical application in assessment and exercise.
| Conclusion |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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| Footnotes |
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* UniQuest Pty Ltd, Level 2, Cumbrae-Stewart Bldg, Research Rd, The University of Queensland, Brisbane, Queensland, 4072 Australia. 
Transducer Techniques Inc, 42480 Rio Nedo, Temecula, CA 92590.
Davidson Measurement Pty Ltd, 1-3 Lakewood Blvd, Braeside, Victoria, 3195 Australia.
National Instruments Corp, 11500 N Mopac Expwy, Austin, TX 78759.
|| Logitech Australia Computer Peripherals Pty Ltd, 3–6 The Strand, Dee Why, New South Wales, 2099 Australia.
# Microsoft Corp, One Microsoft Way, Redmond, WA 98052-6399.
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This article has been cited by other articles:
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  B. Cagnie, N. Dickx, I. Peeters, J. Tuytens, E. Achten, D. Cambier, and L. Danneels The use of functional MRI to evaluate cervical flexor activity during different cervical flexion exercises J Appl Physiol, January 1, 2008; 104(1): 230 - 235. [Abstract] [Full Text] [PDF]
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1) and Day 2 (