MUSCULAR RESPONSE TO SUDDEN LOAD - A TOOL TO EVALUATE FATIGUE AND REHABILITATION

Study Design. Subjects were exposed to fatiguing and restorative inter ventions to assess their response to sudden loads. Objectives. To inve stigate the erector spinae and rectus abdominis response characteristi cs to ''sudden load'' and the effect of fatigue and rehabilitation.Sum mary of Background Data. Unexpected loads, which people often experien ce, can lead to high forces in the spine and may be a cause of low bac k injury. Methods. Muscle responses to sudden load were mediated by fa tigue, walking, expectation, method of load application, exposure to v ibration, and cognitive-behavioral rehabilitation in patients with chr onic low back pain. A novel technique, perfected in this work, called wavelet analysis, was used to analyze these data. Results. Reaction ti me was affected by fatigue and expectation. Vibration exposure signifi cantly increased the muscle response time. Walking was able to amelior ate that effect. Back muscles responded differently, depending on whet her loads were applied to the back through the hands or through the tr unk, Electromyographic reaction time and magnitude decreased in patien ts after a 2-week rehabilitation program. Conclusions. Sudden loads ca n exacerbate fatigue effects, Walking after driving reduces the risk t o the back caused by handling unpredictable loads. Vibration exposure guidelines should be more conservative. Patients have longer response times than healthy subjects, but patients can improve their response t o sudden loads via rehabilitation. Patients exhibit flexion-extension oscillation at 5 Hz in response to a sudden load, suggesting that the 5-Hz, seated, natural frequency observed during whole-body vibration m ay result from neurophysiologic control limits.