Functional changes in back muscle activity correlate with pain intensity and prediction of low back pain during pregnancy.

OBJECTIVE To assess low back pain (LBP) intensity and subjective disability during pregnancy and compare the pain scores with lumbar motion patterns. DESIGN A prospective study of pregnant back pain sufferers and healthy controls. SETTING Kuopio University Hospital, Kuopio, Finland. PARTICIPANTS Study group consisted of 32 pregnant women with LBP; control group consisted of 21 healthy pregnant women. MAIN OUTCOME MEASURES Back pain intensity was assessed by visual analog scale (VAS), and subjective disability index was measured by Oswestry Low Back Disability Questionnaire, at 20 and 36 weeks of pregnancy. Back muscle activities were recorded by surface electromyography, and movement sensors were used to detect lumbar motion. RESULTS In the study group current pain scores (VAS) at first and last trimester correlated strongly (r = .82, p < .00). Pain scores correlated with body weight at the first trimester (r = .54, p = .003) and at the last trimester (r = .67, p < .00). Significant correlation was noted between current pain intensity and back muscle activity level during forward body flexion at first trimester (r = .704, p < .00). Back muscle activity during bending measured at first trimester significantly correlated with pain intensity at last trimester (r = .703, p < .00). Back muscle activity during the first trimester of pregnancy had a negative correlation with current (r = -.57, p = .002) and later subjective disability index (r = -.42, p = .02). It correlated inversely (r = -.54, p = .003) with pain score at last trimester of pregnancy, ie, the lower the back muscle activity at the beginning of pregnancy, the more pain and disability throughout pregnancy. In the control group, three women developed LBP and disability feelings during pregnancy. They had increased muscle activity during flexion at delivery, ie, disturbed flexion relaxation. CONCLUSIONS Prepregnancy LBP predicts renewed pain during pregnancy, and dysfunction of back muscles has been established in LBP. In this study, disturbance in the relaxation of the back muscles was linearly related to current, and also to later, pain scores. In addition, back muscle activity level was inversely related to the disability index. For the first time, it has been shown prospectively that the function pattern of back extensors seems to predict, and is related to, future back pain. Simple function testing is promising and might be valuable in identifying mothers with a high risk of pregnancy-related back pain and in directing preventive intervention to high risk women by making them aware of self-treatment methods.