The thesis describes the electrical activity in nerve cells (motoneurons) that control the deep back muscles in humans. The experiments were conducted using thin wire electrodes that were implanted deep in the spinal muscles in nine acute low back pain patients and in nine healthy, pain free volunteers. The main focus was on the spontaneous, free activation of the postural muscles, which was also compared with voluntary activation. We studied the activity of motoneurons when subjects stood or sat quietly and during voluntary movements. The thesis describes the overall activity, firing discharge, variability in firing and the extent of common drive signals. A main finding was that activity in individual motoneurons to some extent appears to be independent of common control signals, i.e. the nerve cells maintain their activity independently (self-sustained activity). This suggests that the nervous system is able to distribute activity and rest between motoneurons over time (rotation) in the postural muscles of the spine.
We also compared the activity in healthy volunteers with the activity in acute low back pain patients before and after manipulation. The thesis describes a difference in the common drive between nerve cells on opposite sides of the spine in acute low back pain and a difference in firing variability after spinal manipulation. We also describe a different control strategy when the motoneurons fire in free activation of the postural muscles as opposed to under voluntary force production. The possible underlying neurophysiology of these findings is discussed in the thesis.
List of papers. The papers are removed from the thesis due to publisher restrictions.
I: Lothe LR, Raven TJL and Eken T. Single-motor-unit discharge characteristics in human lumbar multifidus muscle. (Submitted).
II: Lothe LR, Raven TJL, Sandbæk G and Eken T. Single-motor-unit discharge characteristics in lumbar multifidus muscle of acute low back pain patients. (Submitted)
III: Lothe LR, Raven TJL, Sandbæk G and Eken T. Single-motor-unit discharge characteristics in lumbar multifidus muscle of acute low back pain patients after spinal manipulation. (Submitted)