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Research Reports |
JW Youdas, PT, MS, is Physical Therapist, Physical Therapy Program, Mayo School of Health-Related Sciences, and Assistant Professor of Physical Therapy, Mayo Medical School, Rochester, Minn. Address all correspondence to Mr Youdas at Mayo Clinic, 200 First St SW, Rochester, MN 55905 (USA) (youdas.james{at}mayo.edu)
TR Garrett, PT, BA, is Physical Therapist, Physical Therapy Program, Mayo School of Health-Related Sciences, and Assistant Professor of Physical Therapy, Mayo Medical School
KS Egan, MPhil, is Statistician, Department of Health Sciences Research, Mayo Clinic and Mayo Foundation
TM Therneau, PhD, is Consultant, Department of Health Sciences Research, Mayo Clinic and Mayo Foundation, and Associate Professor of Biostatistics, Mayo Medical School
Submitted October 20, 1998;
Accepted October 12, 1999
 | Abstract |
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Key Words: Chronic low back pain • Kinesiology/biomechanics • Lumbar spine mobility • Muscle performance
| Introduction |
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 TopAbstract Introduction MethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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Several studies have questioned some of the relationships Kendall et al1 and others2–4 have described regarding faults observed during standing postural alignment. Walker et al5 were the first investigators to examine the relationship between lumbar lordosis and pelvic inclination in standing and abdominal muscle performance. Repeated measurements were made of lumbar lordosis and pelvic tilt in standing on 31 physical therapist students without symptoms of low back pain (23 women and 8 men) between the ages of 20 and 33 years. Abdominal muscle force was assessed with the double-leg lowering test originally described by Kendall et al.1 All measurements were reliable. Spearman rho correlation of abdominal muscle force measurements with pelvic tilt and with lumbar lordosis yielded values of .18 and .06, respectively. The Pearson product-moment correlation coefficient was .32 for the relationship between lordosis and pelvic tilt. Walker et al5 concluded that no relationship existed between lumbar lordosis and pelvic inclination in a standing position and abdominal muscle force.
Similarly, Heino et al6 examined the relationship between hip extension range of motion (ROM) and 3 determinants of standing postural alignment—standing pelvic tilt, depth of lumbar lordosis, and abdominal muscle force—in 25 adults without symptoms of low back pain (15 women and 10 men) between the ages of 21 and 49 years. The Pearson product-moment correlation coefficient was .01 for the relationship between lumbar lordosis and pelvic tilt. The Pearson product-moment correlation coefficient between abdominal muscle force and pelvic tilt was .30, whereas the correlation between abdominal muscle force and lumbar lordosis was .27. No relationship was found among clinical variables commonly observed by physical therapists during a standing postural evaluation of the lumbopelvic complex.
Youdas et al7 sought to expand on the study by Walker et al5 and to examine the association between pelvic inclination and lumbar lordosis during relaxed standing and 8 variables thought to contribute to standing postural alignment. Ninety subjects (45 women and 45 men) between the ages of 40 and 69 years and without back pain or a history of surgery were examined. Multiple linear regression modeling was used to assess the association of pelvic inclination and size of lumbar lordosis in standing with age, sex, body mass index (BMI), physical activity level, back and one-joint hip flexor muscle length, and force and length of abdominal muscles. Abdominal muscle force was associated with angle of pelvic inclination for women (R2=.23) but not for men. Standing lumbar lordosis was associated with abdominal muscle length in women (R2=.40); it was associated multivariately with length of abdominal and one-joint hip flexor muscle and physical activity level in men (R2=.38). Youdas et al used joint range of motion to estimate or reflect muscle length; however, length was not measured directly. The correlation coefficient between pelvic inclination and size of lumbar lordosis was .06 for women and –.08 for men.
Evidence from these 3 studies5–7 challenges the assumption that standing postural malalignments of the pelvis and lumbar spine in subjects without low back pain are linked to abdominal muscle force or tightness of the back and one-joint hip flexor muscles.
Investigators have claimed that anthropometric characteristics such as height and body weight,8 increased lumbar lordosis,9 diminished abdominal muscle force,10 and reduced mobility of the lumbar spine11 by themselves can increase the risk of chronic low back pain (CLBP). It would be important for physical therapists to know whether clusters of these characteristics, which can be objectively measured during a routine clinical examination, are commonly associated with CLBP.
The primary aims of this study were to expand on the study by Youdas et al7 and to determine in patients with CLBP whether an association exists between pelvic inclination or lumbar lordosis during relaxed standing and the following 9 factors: age, sex, BMI, Oswestry Back Pain Disability Questionnaire (ODQ) scores, physical activity level, abdominal muscle force, lumbar extension ROM, lumbar flexion ROM, and one-joint hip flexor muscle length. Furthermore, using data gathered from 90 adults with healthy backs from a previous study,7 we compared the subjects with and without CLBP on the basis of anthropometric characteristics, magnitude of lumbar lordosis, abdominal muscle force, lumbar spine mobility, and physical activity level. We hypothesized that subjects with CLBP would have larger BMIs; an increase in the magnitude of the lumbar lordosis and size of pelvic inclination; and reduced abdominal muscle force, lumbar spine ROM, and levels of physical activity compared with their counterparts without symptoms of low back pain.
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TopAbstractIntroductionMethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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=18.7 years, SD=14.3 years, range=6 months to 44.5 years), and the median duration of back pain for the women was 11 years (=15.4 years, SD=12.7 years, range=1–49 years).
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Subjects were recruited through advertisements placed weekly on bulletin boards at our institution, in monthly newsletters received by our employees, and in a local daily newspaper. All subjects were queried by one of the authors to confirm that they fulfilled each admission criterion: (1) were not currently receiving any treatment for their back pain, (2) had CLBP for at least 4 months,13 (3) were free from major illness, (4) had no previous back surgery, and (5) lacked a spinal fracture, infection, or cancer or occult disease, as determined by plain radiographs, magnetic resonance imaging, or computed tomogram. Written informed consent was obtained from all subjects.
Questionnaires
To allow us to describe the sample more completely, each subject completed 2 brief questionnaires. In the first questionnaire, the Lipid Research Clinics Physical Activity Questionnaire,14 subjects were asked to rate their level of physical activity relative to peers at work and at leisure and to indicate whether they regularly performed (ie, at least 3 times a week) strenuous exercise or hard physical labor (Appendix 2). Based on their answers to the questionnaire, subjects were classified as "very active" if they answered "yes" to questions 3 and 4, "moderately active" if they answered "yes" to question 3 and "no" to question 4, "low active" if they answered "no" to question 3 and rated themselves as active as their peers for questions 1 and 2, and "very low active" if they rated themselves as less active than their peers at work and outside of work and answered "no" to question 3. Ainsworth et al14 reported that data obtained with the Lipid Research Clinics Physical Activity Questionnaire were reliable and valid for predicting cardiorespiratory fitness and body fat. Fifty percent of the women and 60% of the men who volunteered for this study reported engaging in strenuous exercise or hard physical labor at least once a week.
The second questionnaire was the ODQ.15 This instrument was selected so that we could describe the disability level of our subjects with CLBP for the purpose of comparing our results with those of other studies. Subjects completed a self-report that resulted in an index of a patient's perceived disability based on 10 areas of limitation in performance. Each section was scored on a 6-point scale (0–5), with 0 indicating no limitation and 5 indicating maximal limitation. The combined subscales add up to a maximum score of 50. The score was doubled and interpreted as a percentage of patient-perceived disability: the higher the score, the greater the patient's disability. Although the ODQ is described as a disability index, the questionnaire enables the investigator to examine the measures of impairment (eg, pain), functional limitations (eg, sitting, standing, lifting), and disability (eg, personal care, sex life, traveling).
The reliability and validity of scores obtained with the ODQ have been described by Fairbank et al.16 A group of 25 patients with an initial episode of acute low back pain demonstrated a near-linear decrease in their mean ODQ score in a 3-week interval. These authors suggested the ODQ yielded reliable estimates of back pain disability. Twenty-two patients with CLBP completed the ODQ at the same time on 2 consecutive days; the test-retest reliability was estimated by the Pearson product-moment correlation coefficient (r=.99). Grönblad et al17 also examined the reliability for the ODQ in 20 patients with CLBP who completed the ODQ on 2 separate occasions 1 week apart. The test-retest reliability of the disability assessments was estimated by the intraclass correlation coefficient (ICC=.83). These findings suggest that the ODQ provides valid and reliable measurements for predicting disability due to low back pain.
Body Mass Index
We defined body mass index as the ratio of weight (in kilograms) divided by height squared (in square meters).18 Subjects were classified as underweight if the BMI was less than or equal to 20, as having normal weight if the BMI was greater than 20 but less than or equal to 25, as overweight if the BMI was greater than 25 but less than or equal to 30, and as obese if the BMI was greater than 30.19
Physical Activity Status
The physical activity status is a categorical variable with 4 levels (very low, low active, moderate, and highly active). Because only 2 subjects rated themselves as very low active and 5 subjects rated themselves as moderately active, the stability of any model containing categorical variables for levels would be questionable. Therefore, the physical activity status was collapsed to 2 levels. Subjects were classified as either low active (very low to low active on the original scale) or active (moderately to highly active).
Examiners
Measurements were made by 2 of the authors (JWY and TRG), who each had at least 25 years of teaching and clinical experience in physical therapy. Some measurements required the combined effort of both examiners.
Procedure
After the questionnaires were completed, all subjects changed from their street attire into shorts (men) or shorts and a gown (women) to provide adequate exposure of the low back and abdomen. The body height (in inches) and weight (in pounds) of each subject were measured with a standard clinical scale.* The accuracy of this device was checked on a weekly basis. The 2 examiners then measured the following 6 variables: (1) angle of pelvic inclination in a standing position, (2) magnitude of the lumbar lordosis in a standing position, (3) lumbar flexion ROM in a sitting position, (4) lumbar extension ROM in a prone position, (5) length of anterior hip joint soft tissues in a supine position, and (6) force of abdominal muscles in a supine position. Youdas et al7 described the specific procedure for obtaining measurements of each of these variables.
Measurement of pelvic inclination.
Pelvic inclination was measured using an inclinometer (the Back Range of Motion [BROM] II
) and a platform device to control postural sway. Each subject stood barefoot on the platform and was asked to assume a comfortable, erect posture, with body weight evenly distributed between both feet.
Measurement of lumbar lordosis.
Lumbar lordosis was measured with a flexible curve molded to the contour of the subject's lumbosacral spine. Sites along the flexible curve that intersected with adhesive dots marking the spinous processes of T-12, L-4, and S-2 were marked with twist-ties attached to the flexible curve. The shape of the curve's outline was traced on a piece of posterboard, and marks corresponding to the spinous processes were made along the curve's contour. Quantification of the curve (in degrees) was done with a previously described technique that involved drawing tangent lines to the curve at the points representing the spinous processes of T-12, L-4, and S-2.20 Intersections of the 3 tangent lines to the curve at the points representing the spinous processes of T-12, L-4, and S-2 were measured with a protractor, and the sum of the 2 angles was the estimate of the magnitude of the lumbar lordosis.21
Measurement of lumbar spine flexion.
Peak lumbar flexion ROM was also obtained with the flexible curve. With feet flat on the floor and spread to shoulder width, each subject bent the trunk forward, attempting to place the head between the knees. The flexible curve was molded to the contour of the lumbar spine, and its shape subsequently transferred by tracing it onto a piece of posterboard. The curve was quantified (in degrees) using the technique of tangent lines and measuring the angle with a protractor.
Measurement of lumbar spine extension.
Peak lumbar extension ROM was obtained with the subject positioned prone. The subject performed a press-up by placing the palms of the hands at shoulder width, pushing against the table, and passively extending the lumbar spine. The flexible curve was molded to the contour of the subject's lumbar spine. The magnitude of the lumbar extension ROM was obtained by tracing the curve on a piece of posterboard; drawing tangent lines to the marks for spinous processes T-12, L-4, and S-2; and calculating the angles (in degrees) with a protractor.
Measurement of length of one-joint hip flexor muscles.
The procedure to reflect the length of the one-joint hip flexors was patterned after the procedure described by Kendall et al.1 This angular measure was an indirect measurement of muscle length. The subject was initially positioned supine on the treatment table with the hips and knees straight and arms folded across the chest. When assessing the right-side one-joint hip flexors, the examiner passively flexed the subject's left knee so the calf rested against the posterior thigh. The right trunk-thigh angle was obtained with a 360-degree universal goniometer. The angle was used to reflect muscle length.
Measurement of abdominal muscle force.
Abdominal muscle force was measured with the subject positioned supine on a padded wooden treatment table according to a technique originally described by Kendall et al1 and subsequently used by other investigators.5–7 An examiner passively elevated the subject's fully extended legs to a point not exceeding 90 degrees of hip flexion. The subject lowered the legs to the tabletop at the start of a 10-second count, using an eccentric contraction of the hip flexors. During leg lowering, the subject attempted to keep the lumbar spinous processes pressed tightly against the tabletop by maintaining the pelvis in a posterior tilt. Abdominal muscle force was reflected by the angle at the point where the lower back began to extend and the lumbar spinous processes were no longer in contact with the examiner's fingertips. We believe this position change indicated that the abdominal muscles could no longer hold the pelvis in a posterior tilt in response to the ever-increasing external extension moment acting on the lumbar spine primarily through the pull of the psoas major muscles.
For this study, 2 measurements, as described by Youdas et al,7 of each variable were obtained from each subject to permit estimation of intratester reliability in the subjects with CLBP. The time between successive measurements was generally between 2 and 3 minutes. Red adhesive dots used to mark the spinous processes of T-12, L-4, and S-2 were removed after the first examination and replaced by fresh dots before the second examination. The measurement scale of the universal goniometer was blinded from the examiner, and the recorder wrote down the results without conveying any feedback to the examiner. The goniometric measurements did not require the examiner to make any marks on the subject's skin surface. A precursor to answering the main questions was the need to establish the reliability of measurements of the 6 major attributes described in this section.
Except for the indirect measurement of length of the right and left one-joint hip flexors (.60 and .54, respectively), all ICCs were greater than .89 (Tab. 3). The ICC for lumbar extension ROM in the prone position was initially calculated as .73. However, this relationship was highly influenced by 4 outliers. These outliers occurred because the subjects' efforts were inconsistent between the first and second measurements of lumbar extension. Two subjects improved by 16 and 31 degrees, whereas 2 subjects became worse by 14 and 27 degrees. On eliminating these 4 measurements, the remaining 56 measurements yielded an ICC (1,1) of .90.
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Data Analysis
Our study had 2 parts: (1) examining the relationships among variables for people with CLBP and (2) using an unmatched case-control study to determine the relationship of predictor variables to CLBP.
Relationships among variables for subjects with CLBP.
Only the right trunk-thigh angle for estimating the lengths of the one-joint hip flexor muscles was used in the modeling, because the values for left and right sides were highly correlated (r=.66, P=.0001).
Sex was the strongest predictor of pelvic inclination and lumbar lordosis and was highly correlated (P<.0001) with the other independent variables. Therefore, assessment of what other variables might be associated with sizes of lumbar lordosis and pelvic inclination was performed separately for men and women.
The Pearson product-moment correlation coefficient was used to assess the association between lumbar lordosis and degree of pelvic inclination for both men and women. For men (n=30) and women (n=30), each dependent variable was plotted against the 2 measurements (pelvic inclination and lordosis). Following the suggestions of Chambers et al,24 the plots were augmented with a smooth curve to help reveal the pattern of association. The Spearman rank order correlation and associated probability value were used to test for an association between the predictor and pelvic inclination or lumbar lordosis, respectively. Multivariate associations were examined using forward and backward stepwise regression. The study had 80% power to detect a correlation of .35 or greater between a covariate and the response.
Comparing subjects with and without CLBP.
Descriptive statistics for men and women with and without CLBP were compared using the Wilcoxon rank sum test. To examine the relationship of predictor variables to the likelihood of CLBP, the current and prior data sets were analyzed together as an unmatched case-control study. We felt justified in combining the 2 data sets, because their inclusion criteria were identical except the second data set was composed of volunteers with CLBP. Both groups of men and women contained 75 subjects: 30 subjects with CLBP and 45 subjects with healthy backs.
Both univariate and multivariate relationships were examined using the logistic regression model25:
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The smooth functions, S(x), are based on splines. The amount of "wiggle" in the smooth function is controlled by the degrees of freedom (df) for the fit. For a fit with Kdf, place K push pins onto the plot of the data and then spread through them a resilient, flexible metal strip or "spline," attaching it to each of the pins. Two degrees of freedom (pins) lead to a straight line, 3 degrees of freedom lead to a curve with one bend, and n degrees of freedom lead to a curve that intersects every data point. In this analysis, we used 4 degrees of freedom for the smooth terms. All data analyses were performed using the SAS
and S-PLUS
statistical packages.
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TopAbstractIntroductionMethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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Pelvic inclination versus predictor variables.
Figure 1 illustrates the plot of standing pelvic inclination versus each independent variable for both men and women. The Spearman rank order correlation coefficients for men varied from .01 for both abdominal muscle performance and right trunk-thigh angle to .42 for lumbar extension ROM in the prone position. Age (r=.37) and lumbar extension ROM (r=.42) demonstrated an association with pelvic inclination. The correlation coefficients for women varied from .10 for right trunk-thigh angle to .41 for BMI; BMI (r=.41) showed an association with pelvic inclination. There was no observable relationship between standing pelvic inclination and physical activity level.
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Pelvic inclination.
In women, BMI, age, and ODQ scores were associated univariately and multivariately with pelvic inclination (Tab. 5). Once they were accounted for, however, no other variables were significant in the multiple regression model. In men, lumbar extension ROM was related to pelvic inclination. When lumbar extension ROM was accounted for, both age and ODQ scores were significant in the stepwise model.
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Comparing Subjects With and Without CLBP
Descriptive statistics.
Descriptive statistics for men with CLBP (n=30) and men without CLBP (n=45) were compared (Tab. 1) by the Wilcoxon rank sum test. The subjects with CLBP demonstrated weaker abdominal muscles (from 53.9° to 39.4°) and had less lumbar extension ROM (from 42.7° to 50.1°) during a prone press-up than men without CLBP. The BMI (from 28.9 kg/m2 to 26.1 kg/m2) and weight (from 76.7 kg to 67.8 kg) were greater and right (from 180.2° to 180.9°) and left (from 180.4° to 181.6°) trunk-thigh angles and abdominal muscle force were less in women with CLBP (Tab. 2) than in women without CLBP.
Generalized additive models.
The GAMs for men and women were studied separately using the variables weight, height, abdominal muscle force, lumbar lordosis, pelvic inclination, and lumbar extension ROM. Height and weight were selected rather than BMI because they had a greater effect than BMI alone. Right and left trunk-thigh angles were excluded because we failed to detect hip flexion deformity in either the control group or the experimental group. Age was excluded from the model because it was not related univariately to back pain for men or women. Figure 3 shows the plot of the odds ratio of CLBP versus each independent variable for the men. The final model for men was: log[P/(1-p)]=
+ weight + S (height) + abdominal muscle force + S (standing lumbar lordosis) + S (pelvic inclination) + lumbar extension ROM. Height, standing lumbar lordosis, and pelvic inclination demonstrated a nonlinear relationship. Figure 4 shows the plot of the odds ratio of CLBP versus each independent variable for the women. The final model for women was: log[P/(1-p)]= + weight + height + abdominal muscle force + standing lumbar lordosis + pelvic inclination + lumbar extension ROM. All relationships for women were linear. If the odds ratio is 1, then the control subjects are just as likely to experience back pain as those with CLBP. An odds ratio of less than 1 indicates that the subjects are less likely to experience back pain, whereas an odds ratio of greater than 1 indicates that subjects are more likely to have CLBP.
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TopAbstractIntroductionMethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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Relationships Among Variables in Patients With CLBP
Issues involving the ODQ.
The mean ODQ score for the men was 15%, which according to Fairbank et al16 represents minimal disability due to CLBP, whereas the mean ODQ score for women was 26.7% and represents moderate disability. According to Fairbank et al,16 the men in this study should be able to cope with the majority of daily activities (with proper education on how to lift and sit) and maintain a more active lifestyle. In contrast, the women, according to Fairbank et al,16 should experience more pain with lifting, sitting, and standing and may miss work. Nevertheless, their CLBP usually can be managed by conservative treatment.
Issues involving abdominal muscle force.
Contrary to often-expressed opinions,1–4 our data failed to suggest an association between abdominal muscle force and angle of pelvic inclination or lumbar lordosis in relaxed standing in men and women with CLBP. This observation seems counterintuitive to the idea that the abdominal muscles, by pulling upward on the pelvis anteriorly, should have a major effect on the lumbar lordotic curve or angle of pelvic inclination. Some authors have suggested that weak abdominal muscles alter the normal standing postural alignment such that those patients with CLBP demonstrate a visible increase in the standing lumbar lordosis and pelvic inclination.1–4
We argue that assessment of standing postural alignment alone should not be used to prescribe therapeutic strengthening and stretching exercise programs for the trunk muscles in patients with CLBP. Instead, the physical therapist should perform additional tests and measurements to assess the force of the abdominal muscles and the ROM of the lumbar spine.
Issues involving standing lumbar lordosis and lumbar ROM.
Peak prone lumbar extension ROM was univariately and multivariately associated with standing lumbar lordosis for both the men and women. For both groups, the magnitude of standing lumbar lordosis was generally equivalent to the amount of prone back extension. Our data suggest that, at least in patients with moderate disability due to CLBP, the magnitude of the standing lumbar lordosis is equivalent to peak passive lumbar extension in a prone position.
Descriptive Statistics for Comparisons of Subjects With and Without CLBP
Abdominal muscle force.
According to our data, men and women with CLBP had weaker abdominal muscles than their counterparts without low back pain. This finding is consistent with other reports that documented weakness in the abdominal muscles of subjects with CLBP.27–29 It is possible that the poor abdominal muscle force, as measured by the double-leg lowering test, was influenced by pain inhibition rather than being a true decrease in muscle force. This was a potential source of error in this study and is a limitation in any study that measures muscle force in patients with pain.
Standing lumbar lordosis.
Neither the women nor the men with CLBP demonstrated an increased lumbar lordotic curve or angle of pelvic inclination compared with the control subjects. Day et al30 also reported no difference in lumbar lordosis and pelvic inclination in relaxed standing between 32 men without low back pain and 15 men with at least a 3-year history of CLBP. Likewise, Pope et al31 found no difference in the magnitude of lumbar lordosis between 106 adults without low back pain and 215 patients with CLBP.
According to our data, women had a larger mean value for standing lumbar lordosis than men. Using the flexible curve method, our mean value (±SD) for standing lumbar lordosis (37.5°±11°) in 30 men without low back pain, aged 40 to 69 years, was comparable to that from Link et al,32 who examined 61 men without low back pain, aged 20 to 30 years, and reported a mean value of 34.4±9.85 degrees. Frey and Tecklin33 also used the flexible curve technique and reported a mean value of 31.2±14.8 degrees for standing lumbar curvature in 44 subjects without low back pain (22 men and 22 women) whose mean age was 20±2 years. In contrast, the magnitude of lumbar lordosis as measured by the flexible curve is much smaller when compared with values obtained by radiographic techniques. Pope et al31 reported a mean value of 54±11.9 degrees for standing lumbar curvature in 106 subjects without low back pain and a mean value of 53±8.8 degrees for standing lumbar curvature in 144 subjects with moderate low back pain, whereas Jackson and McManus34 reported mean values (±SEM) of 60±12 degrees for 100 adults without low back pain and 56.3±12 degrees for 100 patients with CLBP.
Lumbar spinal mobility.
The effect of CLBP on spinal ROM is not clear. Some investigators35,36 have reported that spinal ROM is diminished in patients with CLBP. In contrast, Esola et al37 reported that patients with CLBP had no less spinal flexion ROM than their counterparts without low back pain. Our results indicated that there was no difference in spinal flexion in both men and women between the subjects with CLBP and the control subjects. Furthermore, women with CLBP had no less lumbar extension ROM from a prone position than their counterparts without low back pain, yet men with CLBP had less lumbar extension ROM than the men without low back pain. This finding is consistent with results reported by Pope et al,31 who also noted diminished lumbar extension ROM in 215 patients with CLBP compared with 106 control subjects. Our data also indicated that peak lumbar extension ROM for both subjects with CLBP and control subjects was considerably greater than peak flexion ROM. Our results are similar to values reported by Troup et al.38
Generalized Additive Models
Through the use of a graphically oriented analytic approach (GAM), we were able to demonstrate some clear patterns regarding the odds ratio of developing CLBP in subjects with minimal to moderate disability according to the ODQ. For both men (Fig. 3) and women (Fig. 4), the odds of developing CLBP decreased as body weight decreased. In terms of height, the odds of having CLBP increased considerably for both men and women above 1.8 m. This relationship was nonlinear for men, as the odds ratio for CLBP was greater than 1 for heights between 1.8 and 1.85 m; however, the ratio diminished sharply thereafter. Men were less likely to have CLBP if their abdominal muscle force, measured by the double-leg lowering test, was less than 50 degrees; for women, we found that the odds ratio of having CLBP was reduced when the abdominal muscle force was less than 60 degrees. These values indicate the point where the lower back began to extend and lumbar spinous processes were no longer in contact with the examiner's fingertips during the double-leg lowering test. In regard to standing lumbar lordosis, the odds ratio of CLBP in women increased once the lumbar curve exceeded 65 degrees. For men, this relationship was nonlinear and the peak lumbar lordosis for subjects with and without CLBP was 60 degrees. For both men and women, the odds of having CLBP was greater with angles of pelvic inclination near 0 degrees. According to our data, the odds ratio of not having CLBP increases in women if the angle of pelvic inclination is greater than 20 degrees. In contrast, for men, the odds ratio for having CLBP increases substantially if the angle of pelvic inclination is greater than 20 degrees. Lastly, both men and women are less likely to have CLBP as passive lumbar extension ROM in the prone position increases. The critical value for men was 30 degrees, whereas the critical value for women was 45 degrees.
Limitations
Our findings regarding the relationships between the independent variables and standing lumbar lordosis and pelvic inclination in patients with CLBP are based on findings from patients with minimal to moderate disability according to the ODQ. Subjects with more severe impairment may demonstrate a stronger relationship between abdominal muscle force and the dependent variables lumbar lordosis and pelvic inclination.
We chose the double-leg lowering test to assess abdominal muscle force because it is familiar to physical therapists. Previous investigators5–7 used this test; although it is complex and requires good neuromuscular control, these investigators documented acceptable intratester reliability in patients with CLBP and their counterparts without low back pain. Nevertheless, physical therapists lack an estimate of the validity of measurements obtained with the double-leg lowering test if it is supposed to be used to predict the size of a subject's lumbar lordosis in standing knowing the grade assigned to the abdominal muscle force.39 In our study, men and women with CLBP statistically demonstrated less force in the abdominal muscles than their counterparts without low back pain. Such weakness may be attributed to low back pain caused by increased abdominal pressure created during the double-leg lowering test.
Another limitation of our study was the use of subjects with CLBP who were not receiving medical treatment at the time the study was conducted. Patients with acute low back pain or CLBP who are receiving medical care may present different findings than our subjects. Furthermore, because our subjects had minimal (men) to moderate (women) disability as a result of CLBP, care must be taken not to generalize our findings to all patients with acute low back pain or CLBP. Furthermore, we also believe there are limitations to using multiple regression analysis with fewer than 10 subjects per covariate; we had 8 covariates and studied 30 men and 30 women. Out findings contribute new information to understanding muscle imbalances associated with standing posture. However, this information should not be considered definitive evidence until additional studies are conducted with larger numbers of subjects.
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TopAbstractIntroductionMethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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Nevertheless, using the GAM analysis, we found that the odds of having CLBP are enhanced as body weight exceeds 100 kg in women and height exceeds 1.8 m for both men and women. Furthermore, the odds ratio of having CLBP is increased if the score on the double-leg lowering test for the abdominal muscles exceeds 50 degrees for men and 60 degrees for women. Additionally, the odds of having CLBP are diminished for both men and women if their passive lumbar extension ROM is greater than 40 degrees.
Abdominal muscle strengthening exercises are routinely recommended by physical therapists to correct faulty standing posture in patients with CLBP. These recommendations are often based on assessment of standing posture. We urge physical therapists to avoid prescribing therapeutic exercise programs of muscle strengthening of abdominal muscles in patients with CLBP based solely on assessment of relaxed standing posture.
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TopAbstractIntroductionMethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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TopAbstractIntroductionMethodResultsDiscussionConclusionAppendix 1Appendix 2References |
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| Footnotes |
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This study was approved by the Mayo Clinic Institutional Review Board.
This research was presented, in part, at Physical Therapy '99: Annual Conference and Exposition of the American Physical Therapy Association; June 7, 1999; Washington, DC.
* Continental Scale Corp, Bridgeview, IL 60455. 
Performance Attainment Associates, 958 Lydia Dr, Roseville, MN 55113.
SAS Institute Inc, PO Box 8000, Cary, NC 27511.
MathSoft Inc, StatSci Division, 1700 Westlake Ave, Seattle, WA 98109.
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