Journal of Occupational Rehabilitation, Vol. 1, No. 2, 1991
Psychological Factors Affecting Isokinetic Trunk Strength Testing in Patients with Work-Related Chronic Low Back Pain Anthony S. Papciak I and Michael Feuerstein t,2
Psychological factors are assumed to play a major role in pain-related work disability. Assessment of pain-related disability using a functional capacity evaluation, usually includes assessment of trunk strength and range of motion. Isokinetic strength testing is a method used to measure strength and function of isolated muscles and has been reported to be an objective, quantifiable assessment of mtnk function. Given that psychological factors are purported to play a role in pain-related disability, it would be important to assess their influence on measurement of physical function. The present study was conducted to assess the influence of psychological variables on isokinetic trunk strength performance. One hundred and eighty-six consecutive male outpatients referred to a work-rehabilitation center were given a functional capacity evaluation. All patients had been out of work for at least 3 months with the chief complaint of low back pain. The evaluation included isokinetic trunk strength testing and measurement o f psychological variables (pain levels, distress, pain coping, pain behaviot, somatization, expectation to return to work) that have been known to contribute to pain-related disability. Data analyses revealed significant correlations among psychological variables and measures of trunk strength and function. The findhNs provide support for a relationship between psychological variables and isokinetic strength testing performance. KEY WORDS: pain; distress; functional capacity evaluation; isokinetic trunk strength tesling.
INTRODUCTION Recently, there has been an increased emphasis on the use of an active rehabilitation approach for those individuals experiencing pain-related work disability. This emphasis on "functional restoration" (1) in work rehabilitation has produced dramatic return to work outcome results (2, 3) with the ability to maintain high 1Center for Occupational Rehabilitation, University of Rochester Medical Center, Rochester, New York. 2Correspondence should be directed to M. Feuerstein, Ph.D., Center for Occupational Rehabilitation, University of Rochester Medical Center, 2337 Clinton Ave. South, Rochester, New York 14618. 95
1053-0487/91/0600-0095506.50/09 1991PlenumPublishingCorporation
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return to work rates at 1-year (2, 3) and 2-year follow-up (4). Integral to the design of individualized rehabilitation programs is the information received from a multidisciplinary functional capacity evaluation. While the scope of information gleaned from such an evaluation varies from practitioner to practitioner, an important measure in the assessment of low back pain disability is trunk strength and range of motion. A commonly observed practice for the objective and quantifiable assessment of trunk function is isokinetic trunk strength testing using a computer-interfaced dynamometer. Isokinetic trunk strength testing is reported to be an advanced method of measuring true spinal range of motion and trunk strength (5). Isokinetic exercise allows for the control of the speed of muscular performance (6). Thus, an isokinetic trunk dynamometer provides a means of objectively measuring the full muscular force potential of a body segment throughout a range of motion but without allowing acceleration to occur. It has been suggested that by testing a muscular system isokinetically, one will obtain an accurate, quantifiable assessment of the isolated muscle system which will indicate the individual's functional capacity (7). It has been suggested that such a measurement is less confounded by response bias and secondary gain influence as are simple self-report measures of pain and dysfunction (5). Isokinetic trunk strength and range of motion are measures used to monitor progress in active work rehabilitation programs (2, 3). A number of psychological variables have been found to be associated with chronic low back pain (8). Pain levels have been reported to lead to decreases in activity levels (9) or avoidance of activity due to fear of future episodes of pain (10). It has been shown that catastrophizing in response to pain is associated with greater distress and poorer adjustment to pain (11). Additionally, patients successfully treated in either an operant behavioral or cognitive-behavioral group format displayed decreased catastrophizing and decreased physical and psychosocial impairment (12). Depression is commonly associated with chronic pain (13), however, there remains much controversy regarding its frequency and etiological significance. Researchers, while analyzing the association between low back pain and other symptoms, found report of frequent worry or tension (anxiety) to be associated with low back pain (14). The tendency to somaticize is associated with report of back pain (15). Personal self-efficacy has been found to influence performance in a physical endurance task (16) and is hypothesized to maintain exercise avoidance in chronic pain patients (17). It appears that psychological variables can exert a potentially significant influence on physical performance in individuals with chronic low back pain. The present study was an investigation of the relationship among psychological variables commonly reported to influence function in individuals with chronic low back pain, and isokinetic trunk strength testing variables. To date, there has been no data reported on the influence of pain level, mood state, belief about managing returning to work, and perception of family's beliefs in ability to return to work on isokinetic trunk strength testing. Such an investigation appears warranted given that isokinetic trunk strength testing has been presented as a "truly objective" means of measuring trunk strength and range of motion.
Isokinetic Trunk Testing
97
METHODS Subjects One hundred and eighty-six consecutive male clients were referred for a functional capacity evaluation at a work rehabilitation center (see Table I for subject characteristics). All subjects were physician referred with the chief complaint of low back pain and had been unable to return to work despite conservative and/or surgical management. All subjects had been out of work at least 3 months and were receiving Worker's Compensation benefits. Informed consent was received by all subjects to participate in a functional capacity evaluation.
Psychometric Instruments The Work Reentry Questionnaire (18) is completed by each subject prior to undergoing an evaluation. It includes questions about demographic variables (age, marital status, education, and date since last worked), pain levels (10-cm visual analog scales rating level of average pain, least pain, and worst pain), and selfefficacy ratings of return to work. These include 10-cm visual analog scale ratings of (1) subject's expectation to return to the workforce (WRQ 26), (2) subject's belief in ability to manage once at work (WRQ 27), (3) subject's rating of family's belief that subject is too ill even to think about returning to work (WRQ 28), and (4) subject's rating of family's belief that subject's condition will deteriorate if subject starts working (WRQ 29). The Millon Clinical Multiaxial Inventory-II (MCMIII) (19) was used to measure anxiety and depression (Anxiety and Dysthymia subscales). The Pain Behavior Scale (20) was used to measure verbal and non-verbal pain behaviors yielding a total score. The Coping Strategies Questionnaire (11) was used to measure cognitive and behavioral coping strategies, as well as the effectiveness of these strategies to control and decrease pain.
Isokinetic Variables Peak Torque represents the maximum muscular force that the muscle or muscle group is capable of producing at the specified speed expressed in footpounds. Peak Torque to Body Weight Ratio is the ratio of peak torque to body weight for both directions of movement (flexion and extension) in a percentage. This ratio divides the peak torque by the body weight for each movement, thus allowing for normalization of torque value by body weight. Range of Motion is the range of movement of a joint expressed in degrees. Coefficient of variation is a statistical term which is an indication of repeatability of measurement (standard deviation divided by the mean) which allows one to determine variability across repetitions (21).
98
Papciak and Feuerstein
Table 1. Subject Characteristics Number of male subjects
186
Age (years) a
38.11(9.5)
Height (inches)~
70.07(3.0)
Weight (pounds)~
195.82(42.2)
Months from last workeda to evaluation
13.86(11.1)
Educational levelb Grade 0-8 Grade 9-11 High school graduate Grade 13-15 (A.A. degree) Grade 16 (B.AJI3.S.) or higher
15(8.2%) 44(23.9%) 94(51.1%) 26(14.1%) 5(2.7%)
Marital statusb Single Married Divorced Widowed Separated
33(18.1%) 121(66.5%) 22(12.1%) I(0.5%) 5(2.7%)
Type of jobb Managerial/professional Technical Service Craft Assembly Farming
16(14.2%) 3(2.7%) 21(18.6%) 39(34.5%) 32(28.3%) 2(1.8%)
a Mean (standard deviation). b Values expressed as percentages.
Apparatus The Loredan Biomedical (Davis, California) isokinetic trunk dynamometer, Model No. 200 300 A, was used to measure trunk muscle performance in the sagittal plane. Subjects were positioned standing in the dynamometer with knees slightly flexed. The axis of rotation of the dynamometer was aligned with the subject's iliac crest. Stabilization was provided by a waist belt and a bolster on the anterior surface of the tibia just distal to the knee. The upper trunk was fastened securely inside a padded carriage attached to the lever arm of the dynamometer. The test speed used in this study was 30 degrees per second. Subjects were allowed five practice trials prior to the collection of the data. Data collection at 30 degrees per second was based on three maximal repetitions of reciprocal flexion and extension followed by one submaximal repetition. The dynamometer was computer interfaced and provided a printout of the test results.
Isokinetic Trunk Testing
99
PROCEDURES Assessment for all subjects proceeded in a standard order. During the study, the same evaluators were used for each subject. Subjects were first weighed and their pulse and blood pressure were recorded. They were given a brief medical screening by a physiatrist and rule-out criteria for evaluation were implemented. If a subject was cleared for evaluation, an informed consent was read, and the subject was asked to voluntarily participate in the remainder of the functional capacity evaluation. The consent form was then signed. The subject was administered a battery of paper and pencil measures by a psychologist. The measures included: Millon Clinical Multiaxial Inventory-II (MCMMI), Work Reentry Questionnaire (ratings for pain levels and likelihood of returning to work), Coping Strategies Questionnaire (pain coping strategies), and Pain Behavior Scale (measures observable pain behaviors). Finally, the subject's trunk strength and range of motion were measured by an exercise physiologist using an isokinetic.trunk dynamometer. At the end of the evaluation, the subjects were debriefed as to the purpose and results of the evaluation.
Statistical Analyses Correlational analyses were performed to assess a relationship among psychological variables and measures of isokinetic trunk strength and range of motion.
RESULTS Pain Report and Pain Behavior Average level of reported pain and pain behavior were negatively correlated with measures of trunk strength (peak torque, peak torque/body weight) and range of motion in flexion and extension. In addition, pain behavior was positively correlated with coefficient of variation in flexion but not extension. Report of worst level of pain was negatively associated with measures of trunk strength and range of motion in extension and flexion except for the measure of peak torque in flexion. Ratings of least pain were negatively associated with range of motion and peak torque to body weight in flexion and extension (see Table II).
Distress Anxiety was negatively correlated "with trunk strength but not range of motion in flexion and extension. Dysthymia was negatively associated with trunk strength in flexion but not extension (see Table III).
Papciak and Feuersteln
100
Table II. P a i n R e p o r t , Pain Behavior, and Isokinetic T r u n k S t r e n g t h Coefficient of variation
Peak torque
Range of motion
Peak torque/body weight
.11 .06 .15 .21 a
-.18 a -.16 -.11 -.37 c
-.28 c -.28 c -.21 a -.42 c
-.24 b -.20 a -.17 a -.45 c
.09 .03
-.25 b -.22 b
-.28 c -.28 c
-.28 c -.26 b
-.01 -.05
-.14 -.41 c
-.21 a -.42 r
-. 19a -.46 c
Flexion VASAVG VASWORST VASLEAST PAIN BEHAVIOR
Extension VASAVG VASWORST VASLEAST PAIN BEHAVIOR
ap
Psychological Factors Affecting Isokinetic Trunk Strength Testing in Patients with Work-Related Chronic Low Back Pain Anthony S. Papciak I and Michael Feuerstein t,2
Psychological factors are assumed to play a major role in pain-related work disability. Assessment of pain-related disability using a functional capacity evaluation, usually includes assessment of trunk strength and range of motion. Isokinetic strength testing is a method used to measure strength and function of isolated muscles and has been reported to be an objective, quantifiable assessment of mtnk function. Given that psychological factors are purported to play a role in pain-related disability, it would be important to assess their influence on measurement of physical function. The present study was conducted to assess the influence of psychological variables on isokinetic trunk strength performance. One hundred and eighty-six consecutive male outpatients referred to a work-rehabilitation center were given a functional capacity evaluation. All patients had been out of work for at least 3 months with the chief complaint of low back pain. The evaluation included isokinetic trunk strength testing and measurement o f psychological variables (pain levels, distress, pain coping, pain behaviot, somatization, expectation to return to work) that have been known to contribute to pain-related disability. Data analyses revealed significant correlations among psychological variables and measures of trunk strength and function. The findhNs provide support for a relationship between psychological variables and isokinetic strength testing performance. KEY WORDS: pain; distress; functional capacity evaluation; isokinetic trunk strength tesling.
INTRODUCTION Recently, there has been an increased emphasis on the use of an active rehabilitation approach for those individuals experiencing pain-related work disability. This emphasis on "functional restoration" (1) in work rehabilitation has produced dramatic return to work outcome results (2, 3) with the ability to maintain high 1Center for Occupational Rehabilitation, University of Rochester Medical Center, Rochester, New York. 2Correspondence should be directed to M. Feuerstein, Ph.D., Center for Occupational Rehabilitation, University of Rochester Medical Center, 2337 Clinton Ave. South, Rochester, New York 14618. 95
1053-0487/91/0600-0095506.50/09 1991PlenumPublishingCorporation
96
Papciak and Feuerstein
return to work rates at 1-year (2, 3) and 2-year follow-up (4). Integral to the design of individualized rehabilitation programs is the information received from a multidisciplinary functional capacity evaluation. While the scope of information gleaned from such an evaluation varies from practitioner to practitioner, an important measure in the assessment of low back pain disability is trunk strength and range of motion. A commonly observed practice for the objective and quantifiable assessment of trunk function is isokinetic trunk strength testing using a computer-interfaced dynamometer. Isokinetic trunk strength testing is reported to be an advanced method of measuring true spinal range of motion and trunk strength (5). Isokinetic exercise allows for the control of the speed of muscular performance (6). Thus, an isokinetic trunk dynamometer provides a means of objectively measuring the full muscular force potential of a body segment throughout a range of motion but without allowing acceleration to occur. It has been suggested that by testing a muscular system isokinetically, one will obtain an accurate, quantifiable assessment of the isolated muscle system which will indicate the individual's functional capacity (7). It has been suggested that such a measurement is less confounded by response bias and secondary gain influence as are simple self-report measures of pain and dysfunction (5). Isokinetic trunk strength and range of motion are measures used to monitor progress in active work rehabilitation programs (2, 3). A number of psychological variables have been found to be associated with chronic low back pain (8). Pain levels have been reported to lead to decreases in activity levels (9) or avoidance of activity due to fear of future episodes of pain (10). It has been shown that catastrophizing in response to pain is associated with greater distress and poorer adjustment to pain (11). Additionally, patients successfully treated in either an operant behavioral or cognitive-behavioral group format displayed decreased catastrophizing and decreased physical and psychosocial impairment (12). Depression is commonly associated with chronic pain (13), however, there remains much controversy regarding its frequency and etiological significance. Researchers, while analyzing the association between low back pain and other symptoms, found report of frequent worry or tension (anxiety) to be associated with low back pain (14). The tendency to somaticize is associated with report of back pain (15). Personal self-efficacy has been found to influence performance in a physical endurance task (16) and is hypothesized to maintain exercise avoidance in chronic pain patients (17). It appears that psychological variables can exert a potentially significant influence on physical performance in individuals with chronic low back pain. The present study was an investigation of the relationship among psychological variables commonly reported to influence function in individuals with chronic low back pain, and isokinetic trunk strength testing variables. To date, there has been no data reported on the influence of pain level, mood state, belief about managing returning to work, and perception of family's beliefs in ability to return to work on isokinetic trunk strength testing. Such an investigation appears warranted given that isokinetic trunk strength testing has been presented as a "truly objective" means of measuring trunk strength and range of motion.
Isokinetic Trunk Testing
97
METHODS Subjects One hundred and eighty-six consecutive male clients were referred for a functional capacity evaluation at a work rehabilitation center (see Table I for subject characteristics). All subjects were physician referred with the chief complaint of low back pain and had been unable to return to work despite conservative and/or surgical management. All subjects had been out of work at least 3 months and were receiving Worker's Compensation benefits. Informed consent was received by all subjects to participate in a functional capacity evaluation.
Psychometric Instruments The Work Reentry Questionnaire (18) is completed by each subject prior to undergoing an evaluation. It includes questions about demographic variables (age, marital status, education, and date since last worked), pain levels (10-cm visual analog scales rating level of average pain, least pain, and worst pain), and selfefficacy ratings of return to work. These include 10-cm visual analog scale ratings of (1) subject's expectation to return to the workforce (WRQ 26), (2) subject's belief in ability to manage once at work (WRQ 27), (3) subject's rating of family's belief that subject is too ill even to think about returning to work (WRQ 28), and (4) subject's rating of family's belief that subject's condition will deteriorate if subject starts working (WRQ 29). The Millon Clinical Multiaxial Inventory-II (MCMIII) (19) was used to measure anxiety and depression (Anxiety and Dysthymia subscales). The Pain Behavior Scale (20) was used to measure verbal and non-verbal pain behaviors yielding a total score. The Coping Strategies Questionnaire (11) was used to measure cognitive and behavioral coping strategies, as well as the effectiveness of these strategies to control and decrease pain.
Isokinetic Variables Peak Torque represents the maximum muscular force that the muscle or muscle group is capable of producing at the specified speed expressed in footpounds. Peak Torque to Body Weight Ratio is the ratio of peak torque to body weight for both directions of movement (flexion and extension) in a percentage. This ratio divides the peak torque by the body weight for each movement, thus allowing for normalization of torque value by body weight. Range of Motion is the range of movement of a joint expressed in degrees. Coefficient of variation is a statistical term which is an indication of repeatability of measurement (standard deviation divided by the mean) which allows one to determine variability across repetitions (21).
98
Papciak and Feuerstein
Table 1. Subject Characteristics Number of male subjects
186
Age (years) a
38.11(9.5)
Height (inches)~
70.07(3.0)
Weight (pounds)~
195.82(42.2)
Months from last workeda to evaluation
13.86(11.1)
Educational levelb Grade 0-8 Grade 9-11 High school graduate Grade 13-15 (A.A. degree) Grade 16 (B.AJI3.S.) or higher
15(8.2%) 44(23.9%) 94(51.1%) 26(14.1%) 5(2.7%)
Marital statusb Single Married Divorced Widowed Separated
33(18.1%) 121(66.5%) 22(12.1%) I(0.5%) 5(2.7%)
Type of jobb Managerial/professional Technical Service Craft Assembly Farming
16(14.2%) 3(2.7%) 21(18.6%) 39(34.5%) 32(28.3%) 2(1.8%)
a Mean (standard deviation). b Values expressed as percentages.
Apparatus The Loredan Biomedical (Davis, California) isokinetic trunk dynamometer, Model No. 200 300 A, was used to measure trunk muscle performance in the sagittal plane. Subjects were positioned standing in the dynamometer with knees slightly flexed. The axis of rotation of the dynamometer was aligned with the subject's iliac crest. Stabilization was provided by a waist belt and a bolster on the anterior surface of the tibia just distal to the knee. The upper trunk was fastened securely inside a padded carriage attached to the lever arm of the dynamometer. The test speed used in this study was 30 degrees per second. Subjects were allowed five practice trials prior to the collection of the data. Data collection at 30 degrees per second was based on three maximal repetitions of reciprocal flexion and extension followed by one submaximal repetition. The dynamometer was computer interfaced and provided a printout of the test results.
Isokinetic Trunk Testing
99
PROCEDURES Assessment for all subjects proceeded in a standard order. During the study, the same evaluators were used for each subject. Subjects were first weighed and their pulse and blood pressure were recorded. They were given a brief medical screening by a physiatrist and rule-out criteria for evaluation were implemented. If a subject was cleared for evaluation, an informed consent was read, and the subject was asked to voluntarily participate in the remainder of the functional capacity evaluation. The consent form was then signed. The subject was administered a battery of paper and pencil measures by a psychologist. The measures included: Millon Clinical Multiaxial Inventory-II (MCMMI), Work Reentry Questionnaire (ratings for pain levels and likelihood of returning to work), Coping Strategies Questionnaire (pain coping strategies), and Pain Behavior Scale (measures observable pain behaviors). Finally, the subject's trunk strength and range of motion were measured by an exercise physiologist using an isokinetic.trunk dynamometer. At the end of the evaluation, the subjects were debriefed as to the purpose and results of the evaluation.
Statistical Analyses Correlational analyses were performed to assess a relationship among psychological variables and measures of isokinetic trunk strength and range of motion.
RESULTS Pain Report and Pain Behavior Average level of reported pain and pain behavior were negatively correlated with measures of trunk strength (peak torque, peak torque/body weight) and range of motion in flexion and extension. In addition, pain behavior was positively correlated with coefficient of variation in flexion but not extension. Report of worst level of pain was negatively associated with measures of trunk strength and range of motion in extension and flexion except for the measure of peak torque in flexion. Ratings of least pain were negatively associated with range of motion and peak torque to body weight in flexion and extension (see Table II).
Distress Anxiety was negatively correlated "with trunk strength but not range of motion in flexion and extension. Dysthymia was negatively associated with trunk strength in flexion but not extension (see Table III).
Papciak and Feuersteln
100
Table II. P a i n R e p o r t , Pain Behavior, and Isokinetic T r u n k S t r e n g t h Coefficient of variation
Peak torque
Range of motion
Peak torque/body weight
.11 .06 .15 .21 a
-.18 a -.16 -.11 -.37 c
-.28 c -.28 c -.21 a -.42 c
-.24 b -.20 a -.17 a -.45 c
.09 .03
-.25 b -.22 b
-.28 c -.28 c
-.28 c -.26 b
-.01 -.05
-.14 -.41 c
-.21 a -.42 r
-. 19a -.46 c
Flexion VASAVG VASWORST VASLEAST PAIN BEHAVIOR
Extension VASAVG VASWORST VASLEAST PAIN BEHAVIOR
ap
