The contribution of the tendon electrode to M-wave characteristics in the biceps brachii, vastus lateralis and tibialis anterior.

In some compound muscle action potentials (M waves) recorded using the belly-tendon configuration, the tendon electrode makes a noticeable contribution to the M wave. However, this finding has only been demonstrated in some hand and foot muscles. Here, we assessed the contribution of the tendon potential to the amplitude of the vastus lateralis, biceps brachii and tibialis anterior M waves, and we also examined the role of this tendon potential in the shoulder-like feature appearing in most M waves. M waves were recorded separately at the belly and tendon locations of the vastus lateralis, biceps brachii and tibialis anterior from 38 participants by placing the reference electrode at a distant (contralateral) site. The amplitude of the M waves and the latency of their peaks and shoulders were measured. In the vastus lateralis, the tendon potential was markedly smaller in amplitude (∼75%) compared to the belly M wave (P = 0.001), whereas for the biceps brachii and tibialis anterior, the tendon and belly potentials had comparable amplitudes. In the vastus lateralis, the tendon potential showed a small positive peak coinciding in latency with the shoulder of the belly-tendon M wave, whilst in the biceps brachii and tibialis anterior, the tendon potential showed a clear negative peak which coincided in latency with the shoulder. The tendon potential makes a significant contribution to the belly-tendon M waves of the biceps brachii and tibialis anterior muscles, but little contribution to the vastus lateralis M waves. The shoulder observed in the belly-tendon M wave of the vastus lateralis is caused by the belly potential, the shoulder in the biceps brachii M wave is generated by the tendon potential, whereas the shoulder in the tibialis anterior M wave is caused by both the tendon and belly potentials. NEW FINDINGS: What is the central question of this study? Does a tendon electrode make a noticeable contribution to the belly-tendon M wave in the vastus lateralis, biceps brachii and tibialis anterior muscles? What is the main finding and its importance? Because the patellar tendon potential is small in amplitude, it hardly influences the amplitude and shape of the belly-tendon M wave of the vastus lateralis. However, for the biceps brachii and tibialis anterior muscles, the potentials at the tendon sites show a large amplitude, and thus have a great impact on the corresponding belly-tendon M waves.

Far-field potentials in hypothenar motor unit number estimation.

INTRODUCTION: Contamination by far-field potentials (FFPs) may interfere with motor unit number estimation (MUNE) in the ulnar nerve. METHODS: Surface motor unit potentials (SMUPs) from 29 spinal and bulbar muscular atrophy (SBMA) patients and 27 control subjects were classified into SMUPs from the abductor digiti minimi muscle (ADM SMUPs) or non-ADM SMUPs, based on the waveform patterns from 3-channel recordings. RESULTS: The mean areas of the ADM SMUPs and non-ADM SMUPs in control subjects were 219.0 ± 131.3 and 63.7 ± 48.5 µVms, respectively. In SBMA patients they were 1988.9 ± 999.4 and 222.7 ± 125.7 µVms, respectively. The percentages of non-ADM SMUPs were 68 ± 22% in controls and 84 ± 15% in SBMA patients. CONCLUSIONS: Non-ADM SMUPs generated mainly by FFPs often had a negative onset in the routine lead and were indistinguishable from ADM SMUPs. More frequent exclusion of smaller non-ADM SMUPs in controls by size criteria would reduce the diagnostic yield of MUNE.

Far-field electric potentials provide access to the output from the spinal cord from wrist-mounted sensors.

Objective. Neural interfaces need to become more unobtrusive and socially acceptable to appeal to general consumers outside rehabilitation settings.Approach. We developed a non-invasive neural interface that provides access to spinal motor neuron activities from the wrist, which is the preferred location for a wearable. The interface decodes far-field potentials present at the tendon endings of the forearm muscles using blind source separation. First, we evaluated the reliability of the interface to detect motor neuron firings based on far-field potentials, and thereafter we used the decoded motor neuron activity for the prediction of finger contractions in offline and real-time conditions.Main results. The results showed that motor neuron activity decoded from the far-field potentials at the wrist accurately predicted individual and combined finger commands and therefore allowed for highly accurate real-time task classification.Significance.These findings demonstrate the feasibility of a non-invasive, neural interface at the wrist for precise real-time control based on the output of the spinal cord.

The influence of the reference electrode location on the M-wave characteristics in the quadriceps.

INTRODUCTION: In the compound muscle action potential (M wave) recorded using the belly-tendon configuration, the contribution of the tendon electrode is assumed to be negligible compared to the belly electrode. We tested this assumption by placing the reference electrode at a distant (contralateral) site, which allowed separate recording of the belly and tendon contributions. METHODS: M waves were recorded at multiple selected sites over the right quadriceps heads and lower leg using two different locations for the reference electrode: the ipsilateral (right) and contralateral (left) patellar tendon. The general parameters of the M wave (amplitude, area, duration, latency, and frequency) were measured. RESULTS: (1) The tendon potential had a small amplitude (<30%) compared to the belly potential; (2) Changing the reference electrode from the ipsilateral to the contralateral patella produced moderate changes in the M wave recorded over the innervation zone, these changes affecting significantly the amplitude of the M-wave second phase (p = 0.006); (3) Using the contralateral reference system allowed recording of short-latency components occurring immediately after the stimulus artefact, which had the same latency and amplitude (p = 0.18 and 0.25, respectively) at all recording sites over the leg. CONCLUSIONS: The potential recorded at the "tendon" site after femoral nerve stimulation is small (compared to the belly potential), but not negligible, and makes a significant contribution to the second phase of belly-tendon M wave. Adopting a distant (contralateral) reference allowed recording of far-field components that may aid in the understanding of the electrical formation of the M wave.

Electrical impedance myography: A critical review and outlook.

Electrical impedance myography (EIM) technology is finding application in neuromuscular disease research as a tool to assess muscle health. Correlations between EIM outcomes, functional, imaging and histological data have been established in a variety of neuromuscular disorders; however, an analytical discussion of EIM is lacking. This review presents an explanation for clinicians and others who are applying EIM and interpreting impedance outcomes. The background of EIM is presented, including the relation between EIM, volume conduction properties, tissue structure, electrode configuration and conductor volume. Also discussed are technical considerations to guide the reader to critically evaluate EIM and understand its limitations and strengths.