Novel methods for quantifying neurophysiologic properties of the human lumbar paraspinal muscles

Utilizing Transcranial Magnetic Stimulation to Study the Human Neuromuscular System

“…For the FCR muscle we place surface electrodes on the forearm using a bipolar electrode arrangement located longitudinally over the muscle on shaved and abraded skin as we have previously described 7,11 . For the erector spinae muscles we use a similar electrode arrangement located longitudinally over the muscles at the L3-L5 vertebral level on shaved and abraded skin 8 . 3.…”

“…Accordingly, when the TMS pulse is delivered during a background contraction, when cortical excitability is increased, the MEP size will dramatically increase. For the ES muscles, we deliver a single TMS pulse to the vertex at an intensity 40 or 50% above the sub-motor threshold intensity 8 . Unfortunately, because peripheral nerves innervating the ES muscles are not accessible to electrical stimulation we are not able to normalize these motor evoked potentials to the compound muscle fiber action potential.…”

“…This conditioning pulse delivered at this time period prior to the test pulse will increase, or facilitate, the amplitude of the motor evoked potential more than a single unconditioned pulse of the same intensity. For the ES muscle group the conditioning pulse intensity is set to the observed sub-motor threshold intensity (either 40% or 50% of stimulator output) and the test pulse intensity is set to 40% above the sub-motor threshold level (80% or 90% of stimulator output) 8 . We should note that the intensity of the conditioning pulses could be varied depending on the objective of the study.…”

“…Additionally, recent advances in magnetic stimulation now allows for partitioning of cortical versus spinal excitability 4,5 . For example, paired-pulse TMS can be used to assess intracortical facilitatory and inhibitory properties by combining a conditioning stimulus and a test stimulus at different interstimulus intervals 3,4,[6][7][8] . In this video article we will demonstrate the methodological and technical aspects of these techniques.…”

“…Specifically, we will demonstrate singlepulse and paired-pulse TMS techniques as applied to the flexor carpi radialis (FCR) muscle as well as the erector spinae (ES) musculature. Our laboratory studies the FCR muscle as it is of interest to our research on the effects of wrist-hand cast immobilization on reduced muscle performance 6,9 , and we study the ES muscles due to these muscles clinical relevance as it relates to low back pain 8 . With this stated, we should note that TMS has been used to study many muscles of the hand, arm and legs, and should iterate that our demonstrations in the FCR and ES muscle groups are only selected examples of TMS being used to study the human neuromuscular system.…”