Quantitative assessment and training of isometric cervical extension strength

Effect of neck flexor muscle activation on impact velocity of the head during backward falls in young adults

Falls are a common cause of traumatic brain injuries (TBI) across the lifespan. A proposed but untested hypothesis is that neck muscle activation influences impact severity and risk for TBI during a fall. We conducted backward falling experiments to test whether activation of the neck flexor muscles facilitates the avoidance of head impact, and reduces impact velocity if the head contacts the ground. Young adults (n=8) fell from standing onto a 30cm thick gymnastics mat while wearing a helmet. Participants were instructed to fall backward and (a) prevent their head from impacting the mat ("no head impact" trials); (b) allow their head to impact the mat, but with minimal impact severity ("soft impact" trials); and (c) allow their head to impact the mat, while inhibiting efforts to reduce impact severity ("hard impact" trials). Trial type associated with peak magnitude of electromyographic activity of the sternocleidomastoid (SCM) muscles (p<0.017), and with the vertical and horizontal velocity of the head at impact (p<0.001). Peak SCM activations, expressed as percent maximal voluntary isometric contraction (%MVIC), averaged 75.3, 67.5, and 44.5%MVIC in "no head impact", "soft impact", and "hard impact" trials, respectively. When compared to "soft impact" trials, vertical impact velocities in "hard impact" trials averaged 87% greater (3.23 versus 1.73m/s) and horizontal velocities averaged 83% greater (2.74 versus 1.50m/s). For every 10% increase in SCM %MVIC, vertical impact velocity decreased 0.24m/s and horizontal velocity decreased 0.22m/s. We conclude that SCM activation contributes to the prevention and modulation of head impact severity during backward falls.

A randomized clinical trial of TENS and exercise for patients with chronic neck pain

Objective: To investigate the effect of transcutaneous electrical nerve stimulation (TENS) on acupuncture points and neck exercise in chronic neck pain patients.

Design: A randomized clinical trial.

Setting: Hospital-based practice.

Subjects: Two hundred and eighteen patients with chronic neck pain.

Interventions: Subjects were randomized into three groups, receiving either (1) TENS over the acupuncture points plus infrared irradiation (TENS group); (2) exercise training plus infrared irradiation (exercise group); or (3) infrared irradiation alone (control); twice a week for six weeks.

Outcome measures: The values of verbal numeric pain scale, Northwick Park Neck Pain Questionnaire, and isometric neck muscle strength were assessed before, at the end of the six-week treatment, and at the six-month follow-up.

Results: Results demonstrated that after the six-week treatment, significant improvement in the verbal numerical pain scale was found only in the TENS group (0.60±2.54, p=0.027) and the exercise group (1.57±2.67, p<0.001). Though significant reduction in Northwick Park Neck Pain Questionnaire score was found in all three groups, post-hoc tests showed that both the TENS and the exercise group produced better improvement (0.38±0.60% and 0.39±0.62% respectively) than the control group (0.23±0.63%). Significant improvement (p = <0.001 to 0.03) in neck muscle strength was observed in all three groups, however, the improvement in the control group was not clinically significant and it could not be maintained at the six-month follow-up.

Conclusions: After the six-week treatment, patients in the TENS and exercise group had a better and clinically relevant improvement in disability, isometric neck muscle strength, and pain. All the improvements in the intervention groups were maintained at the six-month follow-up.

RELIABILITY OF AN ADVANCED METHOD FOR ISOMETRIC NECK MUSCLE STRENGTH MEASUREMENT

This paper is a descriptive study involving repeated within and between studies of maximal isometric strength measurements to determine the reproducibility of an advanced mechanical device in assessing maximal isometric strength of the cervical musculature.

Measurements of neck muscular strength and endurance present unique challenges, due to the complexity of neck motion and absence of appropriate reference bony landmarks. Assessment of cervical musculature characteristics is further complicated by a lack of affordable and reliable measurement equipment. Previous methods commonly employed strain gauge measurement and customized helmet dynamometry, but no device, engaging a computer-controled dynamometer, has been presented so far.

A new device incorporating anthropometry measurements of the local population was constructed for neck strength evaluation on the Biodex isokinetic dynamometer (Biodex, Corp., Shirley, NY). Intratester repeatability testing of the device was conducted in four principal directions: flexion, extension and left and right lateral bending. The result for intraday and day-to-day studies was good for all measured parameters.

This new device can be used to measure isometric flexion, extension and lateral bending torque. By permitting the neck's 'natural' motions, it may also quantify maximal isokinetic strength and endurance ratios. Hence, the device can serve as a useful and practical tool for neck strength measurement, training and rehabilitation purposes.

The assessment of the cervical spine. Part 2: strength and endurance/fatigue

Quantitative documentation of physical deficits such as muscle strength and endurance/fatigue in the cervical spine may provide objective information, not only helping the diagnostic procedures, but also monitoring rehabilitation progress and documenting permanent impairments. The reliable and valid evaluation of muscle strength and endurance both in clinical and research environments are a difficult task since there are many factors that could affect the assessment procedure and the obtained values. The aim of the second part of this critical review is to identify the factors influencing the assessment of strength and endurance/fatigue of the muscles in the cervical spine.

Clinimetric evaluation of methods to measure muscle functioning in patients with non-specific neck pain: a systematic review

Background

Neck pain is a significant health problem in modern society. There is evidence to suggest that neck muscle strength is reduced in patients with neck pain. This article provides a critical analysis of the research literature on the clinimetric properties of tests to measure neck muscle strength or endurance in patients with non-specific neck pain, which can be used in daily practice.

Methods

A computerised literature search was performed in the Medline, CINAHL and Embase databases from 1980 to January 2007. Two reviewers independently assessed the clinimetric properties of identified measurement methods, using a checklist of generally accepted criteria for reproducibility (inter- and intra-observer reliability and agreement), construct validity, responsiveness and feasibility.

Results

The search identified a total of 16 studies. The instruments or tests included were: muscle endurance tests for short neck flexors, craniocervical flexion test with an inflatable pressure biofeedback unit, manual muscle testing of neck musculature, dynamometry and functional lifting tests (the cervical progressive iso-inertial lifting evaluation (PILE) test and the timed weighted overhead test). All the articles included report information on the reproducibility of the tests. Acceptable intra- and inter-observer reliability was demonstrated for t enduranctest for short neck flexors and the cervical PILE test. Construct validity and responsiveness have hardly been documented for tests on muscle functioning.

Conclusion

The endurance test of the short neck flexors and the cervical PILE test can be regarded as appropriate instruments for measuring different aspects of neck muscle function in patients with non-specific neck pain. Common methodological flaws in the studies were their small sample size and an inappropriate description of the study design.

An electromyographic comparison of neck conditioning exercises in healthy controls

The purpose of this study was to compare surface electromyography (EMG) activation levels of selected neck muscles for two common neck-training modalities (Thera-Band and Cybex). Seventeen asymptomatic subjects (eight men and nine women) with a mean age 23.4 years were recruited. EMG activation normalized to maximal voluntary isometric contraction (MVIC) was measured with subjects performing exercises with green, blue, and black Thera-Bands and 50%, 70%, and 90% of 3RM for the Cybex modality. Four variables were used to depict exercise intensity: average and peak EMG activation in the concentric and eccentric phases. Significant differences (P </= 0.05) in EMG activation were evident when comparing intensities of the Cybex modality with each other and when comparing the Cybex intensities with Thera-Band intensities in most cases. Minimal differences were found among differing intensities of Thera-Band. Thera-Band exercise resulted in low-level EMG activation (range, flexion 3.8-15.7% MVIC; range, extension 20.2-34.8% MVIC); therefore, such exercise may be useful in rehabilitation programs. Cybex exercise (range, flexion 20.9-83.5% MVIC; range, extension 40.6-95.8% MVIC) may be useful for occupation-related injury prevention. However, exercise prescription should be undertaken with care as the mechanical loading on passive spinal structures is unknown.

Measurement of cervical flexor endurance following whiplash

AIM

To investigate measurement properties of a practical test of cervical flexor endurance (CFE) in whiplash patients including inter-rater reliability, sensitivity to clinical change, criterion related validity against the Neck Disability Index (NDI), and discriminant validity for injured versus uninjured populations.

METHODS

Two samples were recruited, 81 whiplash patients, and a convenience sample of 160 subjects who were not seeking treatment and met criteria for normal pain and range of motion. CFE was measured using a stopwatch while the subject, in crook lying, held their head against gravity to fatigue.

RESULTS

Inter-rater reliability in whiplash patients was in a range considered 'almost perfect' (Intraclass Correlation=0.96). CFE had greater inter-subject variability than the NDI or range of motion in any of three planes. However, the effect size for improvement in CFE over treatment was as large as the effect sizes for all of those measures. In multivariate regression, CFE changes accounted for changes on the NDI better than the three ranges of motion. CFE discriminated whiplash patients who were within six months of injury (n=71) from age and gender matched normals with high effect size (ES=1.5).

CONCLUSIONS

These findings provide evidence of reliability and validity for CFE measurement, and demonstrate that CFE detects clinical improvements. Variance on CFE emphasizes the need to consider inter-, and intra-subject standard deviations to interpret scores.

Quantification of isometric cervical strength at different ranges of flexion and extension

BACKGROUND

Studies have demonstrated that cervical strength is affected by injury to the neck. Cervical strength measurements are influenced by the protocol used for the measurements. Previous studies have determined the isometric cervical strength only at a few degrees of range of neck motion. The present study was aimed at quantifying cervical strength at neutral, 25%, 50% and 75% of flexion and extension.

METHODS

Using a correlation study design, 39 volunteers in the age range of 18-30 years were recruited in two sessions, one for flexion and the other extension. Their sequence was randomized. The cervical strength was measured using a force measuring device. The device was firmly bolted in the floor. A rotating metal tube was pivoted, adjustably counterweighted and attached to the device at one end and an immovable object with a load cell in its path at the other. The neck was positioned in the desired posture and isometric efforts were exerted on the horizontal resistance arm.

FINDINGS

Cervical strength was found to be highest in the neutral posture for both flexion (19.8 N females and 31.4 N males) and extension (39.5 females and 45.1 males) and significantly decreased with an increasing angular deviation of the neck (P<0.01). Males exerted significantly higher forces than females. The overall flexion-extension ratio was 1:1.7 (P<0.01).

INTERPRETATION

The maximum force was exerted in the neutral posture of the neck and it was directionally dependent being less in flexion than extension (P<0.01). Males were stronger than females. The findings may assist in targeting rehabilitation goals.

Intratester and intertester reliability of neck isometric dynamometry

OBJECTIVE

To evaluate the reproducibility of measurement for maximum voluntary isometric contractions of the cervical musculature in different movements.

DESIGN

Repeated test-retest measurements.

SETTING

A department of physiotherapy.

PARTICIPANTS

Thirty-three healthy subjects (17 men, 16 women; age range, 19-63 y) for the intraexaminer study and 10 healthy subjects (4 men, 6 women; age range, 20-37 y) for the interexaminer study.

INTERVENTIONS

Maximum isometric strength in sitting and standing for flexion, extension, lateral flexion, and rotation using a custom isomyometer device. Three tests, performed 5 to 8 days apart, to assess intraexaminer reliability. Two examiners, each performing 1 trial, measuring on the same day to assess interexaminer reliability.

MAIN OUTCOME MEASURES

Intraexaminer and interexaminer reliability of neck muscle strength.

RESULTS

The standing position showed better reproducibility than the sitting position. The intraclass correlation coefficient (ICC1,3) was above .84 for all tests in any movement and position and above .93 when the first test was excluded. The standard error (SE) of measurement (<16.5 N; <.13 N-m for rotation) and smallest detectable difference (SDD) (<20.1%) were also small. For interexaminer reliability, the ICC(2,1) ranged from.88 to.94 and the SE from 10.7 to 20.8 N (<1.15 N-m for rotation); the SDD was less than 29.8% (except right rotation, which was 38.8%).

CONCLUSIONS

A reliable protocol for measuring neck strength has been developed. Standing position and a full practice session produces more reliable measurements.

Decreased isometric neck strength in women with chronic neck pain and the repeatability of neck strength measurements11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated

OBJECTIVES

To evaluate neck flexion, extension, and, especially, rotation strength in women with chronic neck pain compared with healthy controls and to evaluate the repeatability of peak isometric neck strength measurements in patients with neck pain.

DESIGN

Cross-sectional.

SETTINGS

Rehabilitation center and physical and rehabilitation medicine department at a Finnish hospital.

PARTICIPANTS

Twenty-one women with chronic neck pain and healthy controls matched for sex, age, anthropometric measures, and occupation.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Peak isometric strength of the cervical muscles was tested in rotation, flexion, and extension.

RESULTS

Significantly lower flexion (29%), extension (29%), and rotation forces (23%) were produced by the chronic neck pain group compared with controls. When the repeated test results were compared pairwise against their mean, considerable variation was observed in the measures on the individual level. Intratester repeatability of the neck muscle strength measurements was good in all the 4 directions tested in the chronic neck pain group (intraclass correlation coefficient range,.74-.94). The coefficient of repeatability was 15N, both in flexion and extension, and 1.8 Nm in rotation. On the group level, improvement up to 10% due to repeated testing was observed.

CONCLUSIONS

The group with neck pain had lower neck muscle strength in all the directions tested than the control group. This factor should be considered when planning rehabilitation programs. Strength tests may be useful in monitoring training progress in clinical settings, but training programs should be planned so that the improvement in results is well above biologic variation, measurement error, and learning effect because of repeated testing.

Physical function measurements in neck pain

The literature on physical and functional measurements for the cervical spine is more limited than for the lumbar spine. Most of the studies so far have dealt with the methods for range-of-motion measurements in the cervical spine. These studies indicate that newer computer-guided, three-dimensional measurements systems may provide more precise and reliable data than inclinometer-based techniques and visual estimation methods. The research available also shows a correlation between training and strength improvement in the cervical spine. In addition to physical measurements, several tests have been developed to measure pain level, psychologic factors, disability from neck pain, and generic health, which can assist the clinician in choosing the most appropriate treatment for patients with neck pain. Furthermore, functional measurement systems, such as FCEs, have been developed to describe the functional limitations that a patient may have as a result of a spinal injury. Except for the range-of-motion measurement methods, much more research is required to determine which measurement systems provide the optimal balance between reliability and validity and pragmatic considerations such as time and expense.

Evaluation of cervical range of motion and isometric neck muscle strength: reliability and validity

OBJECTIVE

To examine the test-retest reliability and construct validity of cervical active range of motion and isometric neck muscle strength as measured by the Multi Cervical Rehabilitation Unit (Hanoun Medical Inc., Ontario).

DESIGN

A cross-sectional study.

SETTING

Institutional practice.

SUBJECTS

Twenty-one patients with neck pain and 25 healthy volunteers.

METHODS

After a trial-run session, active range of motion (AROM) was measured in the subsequent two sessions, with 2-3 days in between. During each session, three measurements were taken for each direction (flexion, extension, lateral flexions and rotations). The measurement of isometric strength was after a 15-minute break following completion of the measurement of AROM. Three measurements were made for each of the six directions (flexion, extension, lateral flexions, protraction and retraction). The software of the Multi Cervical Rehabilitation Unit automatically recorded and calculated the maximum AROM and isometric strength.

RESULTS

There was a good to high level of reliability in the measurement of AROM for both groups of subjects, with intraclass correlation coefficients (ICCs) ranging from 0.81 to 0.96. Results also demonstrated very good to excellent reliability in isometric strength measurement (ICCs ranged from 0.92 to 0.99). Moreover, there was a significant difference in isometric neck muscle strength (p = 0.001) and in AROM (p = 0.034) between the two groups.

CONCLUSIONS

The Multi Cervical Rehabilitation Unit was found to be reliable and valid for testing the cervical active range of motion and isometric neck muscle strength for both normal and patient subjects.

Maximal isometric muscle strength of the cervical spine in healthy volunteers

OBJECTIVE

To describe the maximal isometric neck muscle strength in healthy Chinese volunteers, in six different directions, as measured by a Multi Cervical Rehabilitation Unit.

DESIGN

A standardized cross-sectional observational study.

SETTING

A university rehabilitation unit.

SUBJECTS

Ninety-one healthy volunteers aged 20-84.

METHODS

During the measurement the subject was instructed to do three consecutive steady contractions as hard as possible, with a 10-second rest in between each contraction and a 2-minute rest between different directions. The peak isometric strength for each of the six directions (flexion, extension, lateral flexions, protraction and retraction) was calculated.

RESULTS

No significant difference was found in muscle strength between different age groups. Isometric muscle strength in the direction of right lateral flexion was significantly greater than that to the left in men (p = 0.030), but no difference was found in women (p = 0.297). Isometric strength in all directions in men was 1.2-1.7 times that in women (all p < 0.028). Correlations between physical measurements (height and weight) and strength values were all insignificant in both genders.

CONCLUSION

Men have approximately 20-70% greater isometric neck muscle strength than women. Both men and women can maintain high levels of cervical muscle strength in six different directions up to their seventh decade. There is no significant correlation between physical measurements and isometric neck muscle strength.

Two-year follow-up of a randomized clinical trial of spinal manipulation and two types of exercise for patients with chronic neck pain

STUDY DESIGN

Randomized clinical trial.

OBJECTIVES

To compare the effects of spinal manipulation combined with low-tech rehabilitative exercise, MedX rehabilitative exercise, or spinal manipulation alone in patient self-reported outcomes over a two-year follow-up period.

SUMMARY OF BACKGROUND DATA

There have been few randomized clinical trials of spinal manipulation and rehabilitative exercise for patients with neck pain, and most have only reported short-term outcomes.

METHODS

One hundred ninety-one patients with chronic neck pain were randomized to 11 weeks of one of the three treatments. Patient self-report questionnaires measuring pain, disability, general health status, improvement, satisfaction, and OTC medication use were collected after 5 and 11 weeks of treatment and 3, 6, 12, and 24 months after treatment. Data were analyzed taking into account all time points using repeated measures analyses.

RESULTS

Ninety-three percent (178) of randomized patients completed the 11-week intervention phase, and 76% (145) provided data at all evaluation time points over the two-year follow-up period. A difference in patient-rated pain with no group-time interaction was observed in favor of the two exercise groups [F(2141) = 3.2; P= 0.04]. There was also a group difference in satisfaction with care [F(2143) = 7.7; P= 0.001], with spinal manipulation combined with low-tech rehabilitative exercise superior to MedX rehabilitative exercise (P = 0.02) and spinal manipulation alone (P < 0.001). No significant group differences were found for neck disability, general health status, improvement, and OTC medication use, although the trend over time was in favor of the two exercise groups.

CONCLUSION

The results of this study demonstrate an advantage of spinal manipulation combined with low-tech rehabilitative exercise and MedX rehabilitative exercise versus spinal manipulation alone over two years and are similar in magnitude to those observed after one-year follow-up. These results suggest that treatments including supervised rehabilitative exercise should be considered for chronic neck pain sufferers. Further studies are needed to examine the cost effectiveness of these therapies and how spinal manipulation compares to no treatment or minimal intervention.

Neck muscle strength across the sagittal and coronal planes: an isometric study

OBJECTIVE

To determine the maximal isometric strength of neck muscles across different anatomical positions in the body sagittal and coronal planes.

DESIGN

A descriptive study involving maximal isometric strength measurements of the cervical musculature in extension, flexion, and left and right lateral bending. Before measurements, the new device was tested for reliability.

BACKGROUND

The literature contains only a few studies on cervical musculature strength assessment. Of these, measurement methods have displayed weak reliability. No studies existed reporting neck strength at various positions in the body coronal plane.

METHODS

A new device incorporating local population anthropometry was developed for neck strength assessment on an isokinetic dynamometer. The device's repeatability attributes at measuring the strength of functionally different groups of neck muscles were first evaluated. The isometric apparatus was next used to determine the maximal strength of the cervical musculature of 17 healthy volunteers at different anatomical positions across the body sagittal and coronal motion planes.

RESULTS

The results showed good intratester repeatability for intraday and day-to-day studies for all measured parameters. Strength values demonstrated that extensor muscles yielded the greatest torque and that flexor muscles provided the least torque. Linear regression analyses showed strong association of isometric strength with anatomical positions in the two body planes.

CONCLUSIONS

Maximal isometric strength of neck muscles in four directions was quantified. Cervical musculature strength levels vary in discernible patterns with head-neck positions and contraction directions.

RELEVANCE

Knowledge of normative values of neck muscle strength is essential for designing and implementing appropriate rehabilitation programmes. Results from the present study contribute to such literature.

Normative database of isometric cervical strength in a healthy population

OBJECTIVES

This was a descriptive study involving maximal and average isometric strength measurements of the cervical musculature. The purpose of this study was 1) to determine the test-retest reliability of a computerized dynamometer for measuring muscular strength of the neck flexor and extensor muscles in a healthy population, and 2) to afford a normative database of the maximal and averaged isometric strength of the cervical flexors and extensors in a healthy population of 94 volunteers. The literature contains only a few descriptive studies pertaining to strength levels of the cervical musculature; none of these studies used a computerized dynamometer to determine cervical isometric strength. Only a few studies include cervical flexor and extensor isometric strength, evaluating its normal ratio as well as their correlation to body mass index.

METHODS

Testing was carried out using a computerized dynamometer to measure isometric cervical strength at 0 degrees (neutral), 5 degrees, and 10 degrees of flexion and extension of the neck.

RESULTS

Men show approximately 30 to 40% more strength than women both for flexion and extension at all angles and age groups. Neutral positioning showed the maximum strength values for both flexion and extension.

CONCLUSION

There was a significant negative correlation between age and cervical strength and a significant positive correlation between weight and strength and between height and strength. However, the flexor/extensor ratio was maintained around 0.6 in all ages.

Intra- and inter-tester reliability and reference values for isometric neck strength

BACKGROUND AND PURPOSE

Age- and sex-specific reference values for neck strength based on reliable measurements in the upright position are lacking. The aim of the present study was to determine intra- and inter-tester reliability and age- and sex-specific reference values for isometric neck strength in extension, flexion and lateral flexion in sitting position measured with the David Back Clinic 140 (DBC 140) equipment.

METHOD

The reliability of the DBC 140 equipment was investigated in 30 healthy volunteers and reference values were obtained from 101 healthy men and women.

RESULTS

The reliability study showed that neck strength measured with the DBC 140 equipment has almost perfect intra- and inter-tester reliability (ICC values between 0.85 and 0.97). The mean value of the first in a series of three measurements was the highest for all three test leaders and for almost all directions. Results from the reference value study showed that gender is a much more important determinant of neck strength than age, body weight or body mass index (BMI). Neck strength in women was, on average, 55% of that in men, and when adjusted for body weight or BMI, the percentages were 70% and 59%, respectively. In all directions observed, neck strength decreased by approximately 20% from age 25 to 64 years.

CONCLUSIONS

Measurements of neck strength taken in upright position with the DBC 140 equipment have almost perfect intra- and inter-tester reliability and justify the use of this test procedure. The use of the first measurement in a test series can be recommended for use in clinical practice since it was shown to be the maximal test value and thus, had a very low intra-tester difference. The use of reference values for neck strength when evaluating patients with neck disorders needs to take gender into account.

Three-dimensional isometric strength of neck muscles in humans

STUDY DESIGN

Three-dimensional moments were measured experimentally during maximum voluntary contractions of neck muscles in humans.

OBJECTIVES

To characterize the maximum moments with attention paid to subject size and gender, to calculate moments at different locations in the neck, and to quantify the relative magnitudes of extension, flexion, lateral bending, and axial rotation moments.

SUMMARY OF BACKGROUND DATA

Few studies of neck strength have measured moments in directions other than extension, and it is difficult to compare results among studies because moments often are resolved at different locations in the cervical spine. Further, it is not clear how subject size, gender, and neck geometry relate to variations in the moment-generating capacity of neck muscles.

METHODS

Maximum moments were measured in 11 men and 5 women with an average age of 31 years (range, 20-42 years). Anatomic landmarks were digitized to resolve moments at different locations in the cervical spine.

RESULTS

When moments were resolved about axes through the midpoint of the line between the C7 spinous process and the sternal notch, the maximum moments were as follows: extension (men, 52 +/- 11 Nm; women, 21 +/- 12 Nm), flexion (men, 30 +/- 5 Nm; women, 15 +/- 4 Nm), lateral bending (men, 36 +/- 8 Nm; women, 16 +/- 8 Nm), and axial rotation (men 15 +/- 4; women, 6 +/- 3) Nm). The magnitudes of extension, flexion, and lateral bending moments decreased linearly with vertical distance from the lower cervical spine to the mastoid process.

CONCLUSIONS

Moments in three dimensions were quantified with regard to subject size and location along the cervical spine. These data are needed to characterize neck strength for biomechanical analysis of normal and pathologic conditions.

Maximal isometric strength of the cervical musculature in 100 healthy volunteers

STUDY DESIGN

A descriptive study involving maximal isometric strength measurements of the cervical musculature.

OBJECTIVES

To determine the maximal isometric strength of the flexors and extensors and of the cervical musculature in 100 healthy volunteers (50 men and 50 women).

SUMMARY OF BACKGROUND DATA

The literature contains only a few descriptive studies pertaining to strength levels of the cervical musculature. These studies include small subject populations, and measurement methods have demonstrated weak reliability.

METHODS

Testing was carried out using strain-gauge technology on a neck muscle training apparatus.

RESULTS

A reliability study demonstrated acceptable intraday and day-to-day values. Maximal isometric strength was approximately 20% to 25% higher in male subjects than female subjects in both flexion and extension from the third to the sixth decades. In the seventh decade, the women's strength levels surpassed values for men in both flexion and extension. Extension-flexion ratios were approximately 1.7 to 1 in both the men and women participants. The men demonstrated a significant decrease in maximal isometric strength with increasing age in both flexion and extension, whereas the women were able to maintain strength values in the ages tested.

CONCLUSIONS

Men and women demonstrate impressive levels of muscular strength in the flexors and extensors of the cervical spine and can maintain these values until the seventh decade of life. Successful rehabilitation of the cervical musculature will require considerable resistance for sufficient stimulation of the cervical musculature.

Can spinal surgery be prevented by aggressive strengthening exercises? A prospective study of cervical and lumbar patients

OBJECTIVE

To determine if patients recommended for spinal surgery can avoid the surgery through an aggressive strengthening program.

SETTING

A privately owned clinic, staffed by physicians and physical therapists, that provides treatment for patients with neck and/or back pain.

METHODS

Over a period of 2 1/2 years, consecutive patients referred to the clinic for evaluation and treatment were enrolled in the study if they (1) had a physician's recommendation for lumbar or cervical surgery, (2) had no medical condition preventing exercise, and (3) were willing to participate in the approximately 10-week outpatient program. Treatment consisted mainly of intensive, progressive resistance exercise of the isolated lumbar or cervical spine. Exercise was continued to failure, and patients were encouraged to work through their pain. Third-party payors in Minneapolis were surveyed for average costs. Average follow-up occurred 16 months after discharge.

RESULTS

Forty-six of the 60 participants completed the program; 38 were available for follow-up and three required surgery after completing the program.

DISCUSSION/CONCLUSIONS

Despite methodologic limitations, the results are intriguing. A large number of patients who had been told they needed surgery were able to avoid surgery in the short term by aggressive strengthening exercise. This study suggests the need to define precisely what constitutes "adequate conservative care."

Prescription of resistance training for health and disease

When prescribed appropriately, resistance training is effective for developing fitness, health, and for the prevention and rehabilitation of orthopedic injuries. Because resistance training is an integral component in the comprehensive health program promoted by the major health organizations (e.g., American College of Sports Medicine, American Heart Association, American Association of Cardiovascular and Cardiopulmonary Rehabilitation, Surgeon General's Office), population-specific guidelines have recently been published. The current research indicates that, for healthy persons of all ages and many patients with chronic diseases, single set programs of up to 15 repetitions performed a minimum of 2 d x wk(-1) are recommended. Each workout session should consist of 8-10 different exercises that train the major muscle groups. Single set programs are less time consuming and more cost efficient, which generally translates into improved program compliance. Further, single set programs are recommended for the above-mentioned populations because they produce most of the health and fitness benefits of multiple set programs. The goal of this type of program is to develop and maintain a significant amount of muscle mass, endurance, and strength to contribute to overall fitness and health. Patients with chronic diseases (e.g., arthritis) may have to limit range of motion for some exercises and use lighter weights with more repetitions.

Influence of muscle morphometry and moment arms on the moment-generating capacity of human neck muscles

STUDY DESIGN

The function of neck muscles was quantified by incorporating experimentally measured morphometric parameters into a three-dimensional biomechanical model.

OBJECTIVE

To analyze how muscle morphometry and moment arms influence moment-generating capacity of human neck muscles in physiologic ranges of motion.

SUMMARY OF BACKGROUND DATA

Previous biomechanical analyses of the head-neck system have used simplified representations of the musculoskeletal anatomy. The force- and moment-generating properties of individual neck muscles have not been reported.

METHODS

A computer graphics model was developed that incorporates detailed neck muscle morphometric data into a model of cervical musculoskeletal anatomy and intervertebral kinematics. Moment arms and force-generating capacity of neck muscles were calculated for a range of head positions.

RESULTS

With the head in the upright neutral position, the muscles with the largest moment arms and moment-generating capacities are sternocleidomastoid in flexion and lateral bending, semispinalis capitis and splenius capitis in extension, and trapezius in axial rotation. The moment arms of certain neck muscles (e.g., rectus capitis posterior major in axial rotation) change considerably in the physiologic range of motion. Most neck muscles maintain at least 80% of their peak force-generating capacity throughout the range of motion; however, the force-generating capacities of muscles with large moment arms and/or short fascicles (e.g., splenius capitis) vary substantially with head posture.

CONCLUSION

These results quantify the contributions of individual neck muscles to moment-generating capacity and demonstrate that variations in force-generating capacity and moment arm throughout the range of motion can alter muscle moment-generating capacities.

Objectification of functional improvement after nonoperative care

STUDY DESIGN

In this article, the authors review the three broad categories of measures that have been used to objectify functional improvement after nonoperative care of painful spinal disorder patients-physical, psychological, and socioeconomic. For each of the three categories, the major measures used are discussed, as well as research relating to the efficacy of the measures.

OBJECTIVE

To point out the many differences that still exist among research studies regarding which functional outcome measures to use and when to use them.

SUMMARY OF BACKGROUND DATA

During the past few decades, it has been made abundantly clear that painful spinal disorders, particularly when associated with work disability and/or financial benefits, result from a complex interaction of medical, psychological, and social factors. This has resulted in frequent confusion regarding what constitutes the primary roots of the disabling process. Currently, a more comprehensive biopsychosocial perspective of chronic pain and disability has emerged that has significant implications for diagnostic and treatment philosophies of practitioners.

METHODS

Identifying the measures frequently used to address the important biopsychosocial factors, and evaluating their relative benefits and drawbacks.

RESULTS AND CONCLUSIONS

It is demonstrated that there has been an overall trend in recent years toward using more objective, quantifiable instruments, encompassing the physical, psychological, and socioeconomic parameters of outcomes research in painful spinal disorders. These changes will certainly improve the ability of researchers to tease out which factors tap more directly into such tissue as physical impairment, as well as create greater uniformity of measures that will permit direct comparisons between studies.

Strength training: rationale for current guidelines for adult fitness programs

Strength training is an effective method for developing musculoskeletal strength and is often prescribed for fitness, health, and the prevention and rehabilitation of orthopedic injuries. Because strength training is an integral component in the comprehensive health program promoted by the major health organizations (eg, American College of Sports Medicine, American Heart Association, Centers for Disease Control and Prevention, US Surgeon General's Office), population-specific guidelines have recently been published. For the average adult beginning a strength training program, current research indicates that single-set programs performed a minimum of two times per week are recommended over multiple-set programs because they are less time-consuming, more cost-efficient, and produce most of the health and fitness benefits. The goal of this type of program is to develop and maintain a significant amount of muscle mass, endurance, and strength to contribute to overall fitness and health, not to optimize strength, power, and hypertrophy. By incorporating exercise prescription into patient counseling, clinicians can further increase their effectiveness as prevention-oriented healthcare providers.

Neck flexor muscle strength, efficiency, and relaxation times in normal subjects and subjects with unilateral neck pain and headache

OBJECTIVE

To determine the test-retest reliability of a new method for measuring muscular strength, efficiency, and relaxation times of the neck flexor musculature of healthy adults, and to compare these neck flexor muscle properties in subjects who have unilateral neck pain and headache with those in controls.

DESIGN

Subjects lay supine and isometrically flexed their necks against a force transducer attached to the back of a webbing and velcro helmet. Electromyograms (EMGs) were recorded from surface electrodes on the sternocleidomastoid (SCM) muscles. Two consecutive sessions of five contractions of varying levels of effort from minimal through moderate and maximal effort were analyzed.

SETTING

Ambulatory referral center.

PARTICIPANTS

Volunteer control subjects (n = 10, 3 men and 7 women) were recruited from hospital and university personnel. Volunteer neck pain subjects (n = 10, 3 men and 7 women) were recruited from a physiatric chronic pain practice and a hospital outpatient physical therapy practice.

RESULTS

In the controls, the intraclass correlation coefficients (ICCs) for the first two maximum neck flexion contractions were; peak force ICC = .81; peak force/body weight ICC = .75; average force ICC = .75; force relaxation time ICC = .73; SCM EMG relaxation times: right ICC = .60 and left ICC = .67. Comparing sessions 1 and 2 the intraclass correlations for SCM efficiencies were right ICC = .58 and left ICC = .97. The peak force in controls (mean = 45.3 +/- 17.6N) was reduced by 50% in the neck pain subjects (mean = 22.4 +/- 13.1N) (p = .004). Similarly, peak force/body weight in the neck pain subjects (X = 0.3 +/- 0.2N/kg) was 46% of control (mean = 0.7 +/- 0.2N/kg) (p = .001), and average force in the neck pain subjects (X = 12.1 +/- 7.5N) was 43% of controls (mean = 28.5 +/- 11.0N) (p = .001). In two neck pain subjects. SCM, EMG and force relaxation times were abnormally long in both the affected and the unaffected SCM muscles, exceeding the control values by greater than 3 standard deviations. The difference between the right SCM efficiency of the control subjects (mean = 0.3 +/- 0.2N/ microV) and the affected SCM efficiency of the neck pain subjects (mean = 0.1 +/- 0.1 N/microV) approached the p < .05 criterion for significance (p = .055).

CONCLUSION

The technique was found to be highly reliable for the measurement of neck flexor peak force, peak force/body weight, average force, and force relaxation time, and moderately reliable for the quantitation of SCM EMG relaxation times and SCM efficiency. All force values were significantly lower in the neck pain population compared with the controls. In the neck pain population, force and SCM EMG relaxation times, as well as efficiencies, suggested abnormalities. Neck pain subjects showed no significant differences in SCM EMG relaxation time or SCM efficiency between affected and unaffected SCM muscles.

Isometric cervical extension strength of recreational and experienced cyclists

The effect for cyclists of the typical forward sitting position on neck strength and its possible relationship to neck pain have not been examined. The purpose of this study was to measure the peak isometric cervical extension strength (PICES) of both recreational and experienced road cyclists and to compare these values to those of noncyclists. Subjects, 45 men between the ages of 18 and 40, were tested for voluntary PICES through a 126 degrees range of motion on a MedX cervical extension machine. No significant differences were found between the three groups in PICES at any angle. When expressed relative to body weight, significant differences in PICES were found at 126 degrees between the control group and the recreational cyclist group (p < 0.05), and between the control group and the experienced cyclist group (p < 0.01), but not at any other angle. Furthermore, no significant differences in strength were found between cyclists experiencing neck pain and those who did not. These data indicate that the cervical muscles of cyclists have not adapted by increasing maximal isometric strength above that of noncyclists, and that the neck pain frequently reported may be due to fatigue from sustained muscular contractions associated with time spent cycling, rather than from muscle weakness.

Dynamic neck strength training effect on pain and function

This study examined whether neck resistance training could increase strength and reduce pain in workers with a high prevalence of neck disorders. Middle-aged women workers (n = 17) exercised twice weekly for 8 weeks. Each session (12min) consisted of three sets of 12 repetitions of resisted rotation, flexion, and extension muscles using hydraulic dampers. Resistance was set individually and progressively increased every second week. Angle-specific maximal isometric rotator, extensor, and flexor torque was measured before and after training. Torque during rotation, flexion and extension increased (p < .05) on average 35%, 27%, and 19%, respectively, after training. Perceived pain, assessed using a four-graded scale, was reduced (p < .05) after training. It is suggested that 12 minutes of specific neck strength training twice weekly for 8 weeks increases strength of rotator, extensor, and flexor muscles of the neck. Also all individuals who had pain reported reduced perceived neck pain after training.

Frequency and volume of resistance training: effect on cervical extension strength

Quantification of cervical extension (CERV EXT) strength is complicated by the inability to stabilize the torso and isolate the CERV EXT muscles. A newly developed machine designed to stabilize the torso and isolate the CERV EXT muscles was used to evaluate the effect of frequency and volume of resistance training on CERV EXT strength. Fifty men (age, 26 +/- 9 years; height, 174 +/- 16 cm; weight, 74 +/- 9 kg) and 28 women (age, 30 +/- 9 years; height, 152 +/- 32 cm; weight, 62 +/- 7 kg) volunteered to participate. Subjects were randomly stratified to one of four training groups or a control group (CONT, n = 19) that did not train. Each training group exercised for 12 weeks as follows; once per week using one set of dynamic exercise (DYN 1x/wk, n = 14), once per week using one set of DYN and one set of maximal isometric (IM) exercise at eight angles through a 126 degrees-range of CERV EXT (DYN-IM 1x/wk, n = 16), DYN 2x/wk (n = 19), or DYN-IM 2x/wk (n = 10). Maximal IM torque was measured at eight angles initially and after 12 weeks of training. All training groups improved CERV EXT strength (p < or = 0.05) at all angles tested compared to the CONT except for DYN once per week at 0 degree of CERV flexion. A greater increase in strength was found when the groups that trained two times a week were compared to those that trained once per week.(ABSTRACT TRUNCATED AT 250 WORDS)

Validity of Isokinetic and Isometric Testing modalities for Assessing Short-term Resistance Exercise Strength Gains

Although it is generally accepted that human performance must be assessed in a manner specific to the training, previous studies have violated this principle. In order to determine the validity of evaluating short-term resistance training programs with isometric and isokinetic measures, 23 recreationally active males participated in an 8-week training program. Subjects were randomly divided into barbell squat, hip sled, leg extension, and control groups. Pre- and posttesting of quadriceps strength was performed with a Cybex isokinetic dynamometer. Six angle-specific torques (N.m) were determined at 0 rad-s-1 and 1.05 rad-s-1. Ten RM training loads increased significantly for all groups that trained. Isometric torque values differed significantly from isokinetic torque values at 30, 60, 75, and 90° of leg flexion for all groups. No significant torque increases from pre- to posttest were observed for any group at any limb angle for either isometric or isokinetic testing, or for isokinetic peak torque. This indicates that strength increases during short-term dynamic external resistance exercise are not adequately assessed with either isometric or isokinetic evaluations.