Electromyography of the muscle spindle

Abstract

In needle electromyography, there are two spontaneous waveforms, miniature end plate potentials and “end plate spikes”, appearing usually together. Miniature end plate potentials are local, non-propagating postsynaptic waves, caused by spontaneous exocytosis of acetylcholine in the neuromuscular junction. The prevailing hypothesis states that “end plate spikes” are propagated postsynaptic action potentials of muscle fibers, caused by presynaptic irritation of the motor nerve or nerve terminal. Using several small concentric needle electrodes in parallel with the muscle fibers, most “end plate spikes” are strictly local or propagating for 2–4 mm. At the end plate zone, there are miniature end plate potentials without “end plate spikes”. Local “end plate spikes” are junctional potentials of intrafusal gamma neuromuscular junctions of the nuclear bag fibers, and propagated “end plate spikes” are potentials of nuclear chain muscle fibers of muscle spindles. Miniature end plate potentials without “end plate spikes” at the end plate zone derive from alpha neuromuscular junctions. These findings contrast with the prevailing hypothesis. The history of observations and different hypotheses of the origin of end plate spikes are described.

Associations between Deformation of the Thoracolumbar Fascia and Activation of the Erector Spinae and Multifidus Muscle in Patients with Acute Low Back Pain and Healthy Controls: A Matched Pair Case-Control Study

“…We also hypothesize that a possible mechanism behind the observed effects may be adhesions between the fascial layers of the TLF and ESM epimysium, which alters muscle spindle function. Partanen et al [55] recently presented a new method for identifying muscle spindle activity using EMG. It would be interesting to directly investigate the relationships between fascial deformation and muscle spindle activation using this method in a future study and confirm our hypothesis.…”

Associations between Deformation of the Thoracolumbar Fascia and Activation of the Erector Spinae Muscle in Patients with Acute Low Back Pain and Healthy Controls. A Matched Pair Case-Control Study

“…We also hypothesize that a possible mechanism behind the observed effects may be adhesions between the fascial layers of the TLF and ES epimysium, which alters muscle spindle function. Partanen et al [48] recently presented a new method for identifying muscle spindle activity using EMG. It would be interesting to directly investigate the relationships between fascial deformation and muscle spindle activation using this method in a future study and confirm our hypothesis.…”

What if muscle spindles were also involved in the sense of effort?

“…More research is therefore needed to precisely identify the role of fusimotor‐driven afferents in effort perception, especially during such exercises. To that end, the development of muscle spindle electromyography (Partanen et al., 2022) associated with progress in high‐density electromyographic techniques seems promising. According to Cheval and Boisgontier (2021), the current lack of physical activity in high‐income countries may be due in part to people's natural preference for activities associated with low effort perception.…”