Precontractile optical response during excitation-contraction in human muscle revealed by non-invasive high-speed spatiotemporal NIR measurement

Abstract

During muscle contraction the excitation-contraction process mediates the neural input and mechanical output. Proper muscle function and body locomotion depends on the status of the elements in the same process. However, non-invasive and in-vivo methods to study this are not available. Here we show the existence of an optical response occurring during the excitation-contraction process in human biceps brachii muscle. We developed a non-invasive instrument from a photodiode array and light emitting diodes to detect spatially propagating (~5 m/s) and precontractile (~6 ms onset) optical signals closely related to the action potential during electrostimulation. Although this phenomenon was observed 60 years ago on isolated frog muscle cells in the lab, it has not been shown in-vivo before now. We anticipate our results to be a starting point for a new category in-vivo studies, characterising alterations in the excitation-contraction process in patients with neuromuscular disease and to monitor effects of therapy.

Combining Ultrafast Ultrasound and High-Density EMG to Assess Local Electromechanical Muscle Dynamics: A Feasibility Study

“…CMAP conduction velocities were found to be within the physiological range, as reported in literature [1], [31]. The highly repeatable EMG recordings were comparable to other studies that used transcutaneous muscle stimulation [31]- [34]. The stimulation was done on the motor point with low current (< 10mA), and consequently, only superficial muscle fibers were stimulated.…”

“…Since the AP propagates, we expect that the LR effect will propagate as well, resulting in the propagating precontractile response that we observed. LR has been measured extensively in isolated frog muscles, but recently evidence of a similar precontractile response in vivo was found using near-infrared techniques [34]. Using this optical technique a precontractile response temporally coinciding with the EMG activity was found.…”

A Method for Identification of Mechanical Response of Motor Units in Skeletal Muscle Voluntary Contractions Using Ultrafast Ultrasound Imaging—Simulations and Experimental Tests

“…1). Upon neural activation, the muscle fibers are electrically depolarized and give rise to a contraction [3] that results in force production through shortening and thickening of the fibers (mechanical twitch), which is a subtle (micrometer amplitude) and tran-…”

“…Today, electromyography (EMG) is the gold standard to study MUs, and there are multiple techniques available. Invasive needle EMG typically samples electrical potentials at the tip of a needle with a sampling volume of about one mm 3 [6] but provides no quantitative depth or spatial information. Scanning EMG is a spatial extension of the needle EMG The motor unit comprise a bundle of muscle fibers located within a territory and they are controlled by a motor neuron coordinating the activation by a firing pattern.…”

A Deep Learning Pipeline for Identification of Motor Units in Musculoskeletal Ultrasound

“…1A) originating in the spinal cord mediated by the motor neuron. The corresponding output is characterized by repeated electrical depolarizations of the fibers and subsequent repeated shortening and thickening of the fibers (mechanical twitch train) [4] (Fig. 1A and B).…”