Decomposition-based Quantitative Electromyography Research Articles

Average proportional consecutive interval difference accurately differentiates spontaneous activity from motor unit potentials.

An objective method is required to detect spontaneous activity (SA) for prevalence studies in needle electromyography (EMG). Because of frequent similarities in the morphology of SA and motor unit potentials (MUP), identification of SA depends on assessment of firing regularity, which has not yet been quantitated through a modern interface. Prospective recordings obtained from patients referred for electrodiagnostic evaluation were analyzed by using decomposition-based quantitative EMG (DQEMG) customized to calculate descriptive statistics. Forty-four MUP recordings (39 participants) and 80 SA recordings (62 participants) were analyzed. One hundred one of 124 recordings successfully interfaced with DQEMG. The remaining recordings were analyzed in Audacity. Average proportional consecutive interval differences differentiated SA from MUPs with 97.5% sensitivity (confidence interval [CI] 91.3%-99.7%) and 100.0% specificity (CI 92%-100%). There was substantial overlap, however, for SD and mean consecutive differences. Average proportional consecutive interval difference accurately differentiates SA from MUPs and may be useful in future prevalence studies of SA.

Electrophysiological and neuromuscular stability of persons with chronic inflammatory demyelinating polyneuropathy

We assessed motor unit (MU) properties and neuromuscular stability in the tibialis anterior (TA) of chronic inflammatory demyelinating polyneuropathy (CIDP) patients using decomposition-based quantitative electromyography. Dorsiflexion strength was assessed, and surface and concentric needle electromyography were sampled from the TA. Estimates of MU numbers were derived using decomposition-based quantitative electromyography and spike-triggered averaging. Neuromuscular transmission stability was assessed from concentric needle-detected MU potentials. CIDP patients had 43% lower compound muscle action potential amplitude than controls, and despite near-maximum voluntary activation, were 37% weaker. CIDP had 27% fewer functioning MUs in the TA, and had 90% and 44% higher jiggle and jitter values, respectively compared with controls. CIDP had lower strength and compound muscle action potential values, moderately fewer numbers of MUs, and significant neuromuscular instability compared with controls. Thus, in addition to muscle atrophy, voluntary weakness is also due to limitations of peripheral neural transmission consistent with demyelination. Muscle Nerve 56: 413-420, 2017.

Chronic Inflammatory Demyelinating Polyneuropathy: Muscle Atrophy Associated with Denervation and Neuromuscular Transmission Instability

IntroductionChronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired neuropathy of immunological origin. Increased understanding of the pathophysiology of CIDP is of specific interest due to the treatable nature of the disease. It is characterized, in most cases, by symmetrical weakness in proximal and distal muscles that progresses for greater than 2 months. Evidence indicates that disease‐related post‐synaptic damage and muscle fiber atrophy lead to neuromuscular junction remodeling and impaired neuromuscular transmission (Deschenes et al. 2011). The integrity and stability of neuromuscular transmission can be examined using decomposition‐based quantitative electromyography (DQEMG), which can assess the degree of variability in the shape of consecutively detected motor unit potentials (MUPs) termed ‘jiggle’. In this study we compared voluntary and stimulated contractile function, electrophysiological motor unit (MU) properties and muscle volume quantities in a group of CIDP patients (n=11) with a group of age and sex‐matched healthy controls (n=11).MethodsIn an isometric dynamometer, dorsiflexion strength with twitch interpolation to assess voluntary activation, was recorded. Surface and concentric needle electromyographic (EMG) signals were collected from the tibialis anterior (TA). Compound motor action potentials (CMAPs) for the TA were obtained by supra‐maximal stimulation of the fibular nerve. To estimate the number of MUs in the TA the decomposition enhanced spike‐triggered averaging technique was applied. This required subjects to contract at 25% of their maximal voluntary strength for a series of 30s contractions until at least 20 suitable MU trains were acquired. From the intramuscular needle‐detected signals of single MUs, neuromuscular transmission stability was assessed through calculation of MUP ‘jiggle’. Magnetic resonance imaging (MRI) was used to calculate TA muscle volume.ResultsDespite near maximum voluntary activation (~98%), CIDP patients were ~50% weaker and had ~60% lower CMAP amplitudes than controls. The estimated number of functioning MUs in the TA was ~30% fewer in CIDP and with ~68% higher ‘jiggle’ values indicative of greater neuromuscular transmission instability. MRI results indicated that CIDP patients had ~40% less muscle volume in the TA compared to controls. From these preliminary results, those with CIDP have less strength, but are highly activated. They have substantially lower CMAP values and fewer numbers of MUs compared with controls. Neuromuscular stability is also considerably lower in CIDP.ConclusionsVoluntary muscle weakness appears multifactorial and is due to limitations of peripheral neuromuscular transmission, muscle atrophy and moderate MU loss. MRI data indicate atrophy of the TA muscle in CIDP subjects who exhibit approximately half the muscle mass of controls. These measures that detect MU loss, neuromuscular transmission instability and muscle atrophy could be useful for objective assessment of disease severity leading to improved ability to monitor disease progression and treatment outcomes. Furthermore the use of DQEMG could be incorporated into larger studies to help identify CIDP patients in the early stages of neuromuscular degeneration allowing for earlier and perhaps more effective intervention.Support or Funding InformationSupported by NSERC.

Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

ObjectiveTo study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). MethodsThe tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77±5years) and 9 young male control subjects (23±0.3years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. ResultsNF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P<0.05). NF jiggle was significantly higher in the TA compared to VM (P<0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P<0.05). For VM, NF jiggle was positively correlated with NF count and MUP area (P<0.05), and no significant correlations were found between NF jiggle and S-MUP amplitude, MUP duration, or MUP peak-to-peak voltage (MUNE was not calculated for VM, so no correlation could be made). ConclusionsHealthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG. SignificanceNF jiggle derived from DQEMG can be a useful method of identifying neuromuscular dysfunction at various stages of MU remodeling and aging.

Increased neuromuscular transmission instability and motor unit remodelling with diabetic neuropathy as assessed using novel near fibre motor unit potential parameters

ObjectiveTo assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in patients with diabetic polyneuropathy (DPN) using decomposition-based quantitative electromyography (DQEMG) and near fibre (NF) motor unit potential (MUP) parameters. MethodsThe tibialis anterior (TA) muscle was tested in 12 patients with DPN (65±15years) and 12 controls (63±15years). DQEMG was used to analyze electromyographic (EMG) signals collected during voluntary contractions. MUP and NF MUP parameters were analyzed. NF MUPs were obtained by high-pass filtering MUP template waveforms, which isolates contributions of fibres that are close to the needle detection surface. NF MUP parameters provided assessment of motor unit size (NF area), fibre density (NF fibre count) and contribution dispersion (NF dispersion) and neuromuscular transmission instability (NF jiggle). ResultsDPN patients had larger (+45% NF area), more complex (+30% NF fibre count), and less stable (+30% NF jiggle) NF MUPs (p<0.05). No significant relationships were found between NF MUP stability and denervation, or strength; however NF MUP complexity was positively related to TA denervation in the DPN group (r=0.63; p<0.05). NF MUP complexity and instability were positively related in DPN patients (r=0.46; p<0.05). ConclusionsDPN is associated with neuromuscular transmission instability and MU remodelling that can be assessed using DQEMG. SignificanceDQEMG-derived NF MUP parameters may be useful in identifying patients in early stages of neuromuscular dysfunction related to DPN.

Neuromuscular remodeling and neuromuscular junction instability in human diabetic neuropathy (1168.1)

Diabetic polyneuropathy (DPN) is a progressive axonopathy marked by loss of motor fibers, compensatory collateral reinnervation and reduced stability of neuromuscular transmission. Our objective was to assess the degree of reinnervation and motor unit instability in patients with DPN using decomposition‐based quantitative electromyography (DQEMG). Additionally, relationships between motor unit stability and muscle function were examined. The tibialis anterior (TA) muscle was tested in twelve patients with DPN (65 ± 15 yrs) and 12 age‐matched controls (63 ± 15 yrs). DQEMG was used to analyze surface and intramuscular EMG signals recorded from the TA during moderate voluntary dorsiflexion contractions. Individual motor unit action potential (MUP) trains were identified and analyzed for: MUP size (peak to peak amplitude, area), complexity (turns, fiber dispersion) and stability (near fiber jiggle). DPN patients featured larger (+45% MUP area), more complex (+40% fiber dispersion), and less stable (+30% near fiber jiggle) MUPs (p&lt;0.05). No significant relationships were found between MUP stability and muscular denervation, or strength. MUP complexity and instability were positively related in DPN patients (r=0.46; p&lt;0.05) and controls (r=0.37; p&lt;0.05). DPN is associated with neuromuscular remodeling which leads to increasingly impaired neuromuscular transmission that is detectable using DQEMG.Grant Funding Source: NSERC

Pilot study: quantification of motor unit stability, or “jiggle”, in amyotrophic lateral sclerosis (731.11)

Loss of motor units (MUs) have been found in aging, neuropathies, and motor neuron diseases. With MU loss, subsequent collateral reinnervation results in unstable motor unit potentials (MUPs) with variability in firing times and generation of muscle fiber action potentials. Jiggle is a measure of MUP stability, which can be calculated using Decomposition‐based Quantitative Electromyography (DQEMG). Two previous studies have attempted to measure jiggle, but both studies were limited by the EMG decomposition algorithms used. The purpose of this study is to measure jiggle in the upper trapezius muscle of 11 amyotrophic lateral sclerosis (ALS) patients compared to age‐matched healthy controls. Jiggle will be calculated using the normalized value of the median consecutive amplitude difference (CAD). Jiggle will also be compared to other MUP parameters including motor unit number estimation (MUNE), mean surface MUP (S‐MUP) size, MUP amplitude, and near fiber count. As a result of denervation and incomplete reinnervation, we expect to see significantly higher jiggle values in patients with ALS relative to controls. We also expect jiggle to be negatively correlated with MUNE, and positively correlated with mean S‐MUP size, MUP amplitude, and near fiber count. If successful, jiggle may be a valuable diagnostic parameter or outcome measure in age‐related sarcopenia, neuropathies, or motor neuron diseases such as ALS.

Length dependent loss of motor axons and altered motor unit properties in human diabetic polyneuropathy

ObjectiveTo assess the number and properties of motor units in an upper and lower limb muscle (tibialis anterior [TA] and first dorsal interosseous [FDI]) in human diabetic polyneuropathy (DPN) using decomposition-based quantitative electromyography (DQEMG). MethodsDQEMG protocols were performed in the TA and FDI of 12 patients with confirmed diabetes mellitus and associated DPN, as well as 12 age-matched control participants. Maximal dorsiflexion strength was also assessed using a dynamometer. ResultsIn both muscles, patients with DPN had significantly reduced motor unit number estimates (MUNEs) (ΔTA ∼45%; ΔFDI ∼30%), compound muscle action potentials (CMAPs) (ΔTA ∼30%; ΔFDI ∼20%), and mean firing rates were reduced (ΔTA ∼15%; ΔFDI ∼15%) compared to controls (p<0.05). For the TA, patients with DPN had larger mean surface motor unit potentials (SMUPs) (ΔTA ∼40%; p<0.05), whereas in the FDI no differences were found (p>0.05). ConclusionsDPN may result in motor unit loss, remodeling, and altered firing rate patterns. The magnitude of changes in the neuromuscular properties of DPN patients are muscle dependent and reflect a length-dependent disease progression. SignificanceDQEMG may be a clinically useful technique in identifying the presence and severity of neuromuscular pathophysiology and tracking disease progression in DPN.

Decomposition‐based quantitative electromyography in the evaluation of muscular dystrophy severity

Electromyography is useful in the diagnosis of myopathies, but its utility in determining disease severity requires further investigation. In this study we aimed to determine whether decomposition-based quantitative electromyography (DQEMG) could indicate the severity of involvement in a cohort of patients with muscular dystrophies (MDs). Fifteen patients with facioscapulohumeral (FSHD), limb-girdle (LGMD), and Becker (BMD) muscular dystrophy, and 7 healthy controls, participated in this investigation. Knee extensor isometric strength differentiated the "more severe" and "less severe" MD groups. The vastus lateralis (VL), biceps brachii (BB), and tibialis anterior (TA) muscle groups were investigated using DQEMG. All muscles from the MD group showed changes in mean MUP (motor unit potential) AAR (area-to-amplitude ratio), and turns, compared with controls (P < 0.05). More severely affected muscles (VL and BB) also had shortened mean MUP durations compared with controls (P < 0.01). DQEMG was capable of indicating the severity of MD involvement, as changes in MUP morphology reflected the progressive nature of the disease.

Intra- and inter-rater reliability of motor unit number estimation and quantitative motor unit analysis in the upper trapezius

Objective To collect normative data and assess the intra- and inter-rater reliability of decomposition-enhanced spike-triggered averaging (DE-STA) motor unit number estimation (MUNE) and quantitative MU analysis obtained using decomposition-based quantitative electromyography (DQEMG) in the upper trapezius (UT). Methods In 10 control subjects, the experimental protocol was performed twice by the same examiner, and once by a second examiner. Results Mean MUNE values were 339 ± 121 (rater 1a), 320 ± 131 (rater 1b), and 262 ± 115 (rater 2) MUs. Intra- and inter-rater reliability was good for maximum CMAP (ICC = 0.77 and 0.79, respectively) and moderate for MUNE (ICC = 0.69 and 0.73, respectively), with poor inter-rater reliability for mean S-MUP (ICC = 0.42). Significant differences between rater 1a and 2 were found for mean S-MUP ( p = 0.014) and MUNE ( p = 0.002), and moderate to good levels of reliability found for quantitative needle-detected MUP parameters. Conclusions Various components of the protocol may have contributed to mean S-MUP variability, and may require particular attention in a large, proximal muscle like the UT. Significance This study has established preliminary data using DQEMG in a novel muscle which may be relevant to study in patients with ALS.

Assessing motor deficits in compressive neuropathy using quantitative electromyography

BackgroundStudying the changes that occur in motor unit potential trains (MUPTs) may provide insight into the extent of motor unit loss and neural re-organization resulting from nerve compression injury. The purpose of this study was to determine the feasibility of using decomposition-based quantitative electromyography (DQEMG) to study the pathophysiological changes associated with compression neuropathy.MethodsThe model used to examine compression neuropathy was carpal tunnel syndrome (CTS) due to its high prevalence and ease of diagnosis. Surface and concentric needle electromyography data were acquired simultaneously from the abductor pollicis brevis muscle in six individuals with severe CTS, eight individuals with mild CTS and nine healthy control subjects. DQEMG was used to detect intramuscular MUPTs during constant-intensity contractions and to estimate parameters associated with the surface- and needle-detected motor unit potentials (SMUPs and MUPs, respectively). MUP morphology and stability, SMUP morphology and motor unit number estimates (MUNEs) were compared among the groups using Kruskal-Wallis tests.ResultsThe severe CTS group had larger amplitude and longer duration MUPs and smaller MUNEs than the mild CTS and control groups, suggesting that the individuals with severe CTS had motor unit loss with subsequent collateral reinnervation, and that DQEMG using a constant-intensity protocol was sensitive to these changes. SMUP morphology and MUP complexity and stability did not significantly differ among the groups.ConclusionsThese results provide evidence that MUP amplitude parameters and MUNEs obtained using DQEMG, may be a valuable tool to investigate pathophysiological changes in muscles affected by compressive motor neuropathy to augment information obtained from nerve conduction studies. Although there were trends in many of these measures, in this study, MUP complexity and stability and SMUP parameters were, of limited value.

High inter-rater reliability in analyzing results of decomposition-based quantitative electromyography in subjects with or without neuromuscular disorder

Decomposition-based quantitative electromyography (DQEMG) comprises a group of methods used to obtain information related to the health of the neuromuscular system. Although primarily objective, aspects of the data analysis protocol include operator decisions that may impact its reliability and reduce the applicability of the technique among multiple users. Thus, the objective of this study was to establish the inter-rater reliability of the protocol used for DQEMG analysis among five raters. Seventy data files previously obtained using DQEMG from healthy control subjects and patients with disorders of the neuromuscular system were analyzed by four novice and one experienced rater. Values obtained from this analysis were then evaluated for reliability within the novice raters and in contrast to the results of the experienced rater to examine the influence of the level of rater experience on the results obtained. The majority of the parameters associated with the number of motor unit potentials and their physiological characteristics were found to be reliable among all raters, with moderate-high ICC values observed for both the biceps brachii and first dorsal interosseous muscles. The data suggest that the level of rater experience does not greatly influence the results obtained and that the analysis can be reliably performed by a rater who is given suitable instruction. These findings are important particularly given the potential use of DQEMG as an outcome measure in multi-center studies.

Inter-rater reliability of motor unit number estimates and quantitative motor unit analysis in the tibialis anterior muscle

To establish the inter-rater reliability of decomposition-based quantitative electromyography (DQEMG) derived motor unit number estimates (MUNEs) and quantitative motor unit (MU) analysis. Using DQEMG, two examiners independently obtained a sample of needle and surface-detected motor unit potentials (MUPs) from the tibialis anterior muscle from 10 subjects. Coupled with a maximal M wave, surface-detected MUPs were used to derive a MUNE for each subject and each examiner. Additionally, size-related parameters of the individual MUs were obtained following quantitative MUP analysis. Test-retest MUNE values were similar with high reliability observed between examiners (ICC=0.87). Additionally, MUNE variability from test-retest as quantified by a 95% confidence interval was relatively low (+/-28 MUs). Lastly, quantitative data pertaining to MU size, complexity and firing rate were similar between examiners. MUNEs and quantitative MU data can be obtained with high reliability by two independent examiners using DQEMG. Establishing the inter-rater reliability of MUNEs and quantitative MU analysis using DQEMG is central to the clinical applicability of the technique. In addition to assessing response to treatments over time, multiple clinicians may be involved in the longitudinal assessment of the MU pool of individuals with disorders of the central or peripheral nervous system.

Motor unit potential morphology differences in individuals with non-specific arm pain and lateral epicondylitis

BackgroundThe pathophysiology of non-specific arm pain (NSAP) is unclear and the diagnosis is made by excluding other specific upper limb pathologies, such as lateral epicondylitis or cervical radiculopathy. The purpose of this study was to determine: (i) if the quantitative parameters related to motor unit potential morphology and/or motor unit firing patterns derived from electromyographic (EMG) signals detected from an affected muscle of patients with NSAP are different from those detected in the same muscle of individuals with lateral epicondylitis (LE) and/or control subjects and (ii) if the quantitative EMG parameters suggest that the underlying pathophysiology in NSAP is either myopathic or neuropathic in nature.MethodsSixteen subjects with NSAP, 11 subjects with LE, eight subjects deemed to be at-risk for developing a repetitive strain injury, and 37 control subjects participated. A quantitative electromyography evaluation was completed using decomposition-based quantitative electromyography (DQEMG). Needle- and surface-detected EMG signals were collected during low-level isometric contractions of the extensor carpi radialis brevis (ECRB) muscle. DQEMG was used to extract needle-detected motor unit potential trains (MUPTs), and needle-detected motor unit potential (MUP) and surface detected motor unit potential (SMUP) morphology and motor unit (MU) firing rates were compared among the four groups using one-way analysis of variance (ANOVA). Post hoc analyses were performed using Tukey's pairwise comparisons.ResultsSignificant group differences were found for all MUP variables and for MU firing rate (p < 0.006). The post-hoc analyses revealed that patients with NSAP had smaller MUP amplitude and SMUP amplitude and area compared to the control and LE groups (p < 0.006). MUP duration and AAR values were significantly larger in the NSAP, LE and at-risk groups compared to the control group (p < 0.006); while MUP amplitude, duration and AAR values were smaller in the NSAP compared to the LE group. SMUP duration was significantly shorter in the NSAP group compared to the control group (p < 0.006). NSAP, LE and at-risk subjects had lower mean MU firing rates than the control subjects (p < 0.006).ConclusionThe size-related parameters suggest that the NSAP group had significantly smaller MUPs and SMUPs than the control and LE subjects. Smaller MUPs and SMUPs may be indicative of muscle fiber atrophy and/or loss. A prospective study is needed to confirm any causal relationship between smaller MUPs and SMUPs and NSAP as found in this work.

Reliability of quantitative EMG analysis of the extensor carpi radialis muscle

This study investigated the within-subject, intra- and inter-operator reliability of quantitative electromyographic (EMG) analysis using decomposition-based quantitative electromyography (DQEMG). Needle and surface-detected EMG signals were collected during low-level isometric contractions of the extensor carpi radialis (ECR) muscle. DQEMG was used to extract needle-detected motor unit potential (MUP) trains and surface-detected MUPs (SMUPs) associated with each train. Two independent experienced operators re-decomposed and processed the MUP data on two separate occasions. One-way analyses of variance (ANOVA) were performed to identify within-subject differences (test–retest, n = 6), and operator and trial differences (intra- and inter-operator, n = 20) for the MUP morphological variables. The within-subject reliability, as well as the intra- and inter-operator reliability were estimated using intraclass correlation coefficients (ICCs). The 95% limits of agreement were calculated to measure within-subject and between operator agreements. MUP durations were found to be significantly different between days ( p < 0.05). For intra- and inter-operator reliability, a significant difference was found within and between the operators for MUP duration, and between the operators for MUP number of turns ( p < 0.05). SMUP morphological parameters yielded higher ICC values for both intra (0.96–0.99) and inter (0.96–0.99) operator scores when compared to MUP morphological parameters (intra-operator: 0.81–0.99; and inter-operator: 0.67–0.98). Mean motor unit (MU) firing rate was found to be a highly reliable measure for both intra- and inter-operators (0.99–0.97, respectively). The between-operator agreement was above 95% for all morphological parameters. These results concerning within-subject, intra- and inter-operator reliability and levels of agreement for quantitative motor unit analysis suggest that DQEMG provides sufficiently consistent results to allow it to be effectively used for QEMG analysis. Needle-detected MUP morphology although clinically useful in the diagnosis and monitoring of neuropathies, was not as reliable as surface MUP QEMG measures.

Motor unit number estimates and quantitative motor unit analysis in healthy subjects and patients with amyotrophic lateral sclerosis

Limitations associated with global measures of function in patients with amyotrophic lateral sclerosis (ALS) and the qualitative nature of needle electromyography have stimulated the development of alternate means of monitoring disease severity and progression in ALS. Thus, the objective of this study was to examine the ability of one these techniques, decomposition-based quantitative electromyography (DQEMG), to obtain electrophysiological data, including motor unit number estimates (MUNEs), from a group of patients with ALS. The first dorsal interosseous and biceps brachii muscles were studied in 10 healthy subjects and 9 patients with ALS. Following the acquisition of a maximum M wave, needle- and surface-detected EMGs were collected simultaneously during 30-second contractions performed at 10% of the maximum voluntary contraction force to obtain motor unit potential (MUP) trains. DQEMG was then used to extract the surface-detected MUP associated with each MUP train, the mean size of which was divided into the maximum M wave to obtain a MUNE. The results suggest that quantitative electrophysiological data obtained using DQEMG are representative of the pathophysiological changes in the lower motor system in ALS patients, supporting its use in studies documenting the natural history and progression of the disease.

Physiological characteristics of motor units in the brachioradialis muscle across fatiguing low-level isometric contractions

The purpose of this study was to determine (i) if decomposition-based quantitative electromyography (DQEMG) could detect changes in motor unit potential (MUP) morphology and motor unit (MU) firing pattern statistics associated with muscle fatigue, (ii) if any detected changes are correlated with surface electromyographic (SEMG) signs of fatigue, and (iii) if significant fatigue-dependent changes are repeatable within individuals. Mean MU firing rates and the morphology of MUPs detected using needle and surface electrodes during constant-torque isometric contractions held until exhaustion were investigated in the brachioradialis (BR) muscle in 10 healthy volunteers (mean age = 28.6 yr, SD ± 3.9). Time dependant changes were investigated using an analysis of variance with normalized time as a main effect. Partial correlation coefficients were computed using a repeated measures analysis of covariance to determine if changes in MU firing rates, needle-detected MUPs and surface-detected MUPs (SMUPs) were related to changes in SEMG signal amplitude and frequency parameters. Intraclass correlation coefficients (ICCs) were used to determine the within-subject repeatability of changes in MU firing rates, and MUP and SMUP parameters. Significant decreases in mean MU firing rates were found along with significant increases in various duration and area related parameters in both MUPs and SMUPs across the fatiguing contraction. The SEMG signal demonstrated the expected changes with fatigue: an increase in amplitude and a decrease in frequency content. SEMG amplitude was significantly positively correlated with SMUP peak-to-peak voltage ( r = 0.85, p < 0.05), and SMUP area ( r = 0.86, p < 0.05). Mean power frequency was significantly negatively correlated with SMUP negative peak duration ( r = −0.74, p < 0.05). The significant time-dependent changes were reliably observed (ICCs were 0.94 for MUP peak to peak amplitude, 0.97 for MUP area and 0.95 for MUP area to amplitude ratio, 0.95 for SMUP peak-to-peak voltage, 0.83 for SMUP area, 0.99 for SMUP negative peak amplitude and 0.88 for SMUP negative peak area). The decreases in mean MU firing rates measured along with the increases in amplitude, duration and area parameters of MUPs and SMUPs and their partial correlation with SEMG amplitude during submaximal fatiguing contractions of the BR, suggest that recruitment is a main cause of increased SEMG amplitude parameters with fatigue. We conclude that DQEMG can be effectively and reliably used to detect changes in physiological characteristics of MUs that accompany fatigue.

Firing Characteristics of Motor Units during the First 90 Seconds of a Fatiguing Low-Level Contraction

The mechanisms responsible for the changes in surface electromyographic (EMG) signal amplitude and frequency content during prolonged fatiguing low-level contractions are not well understood. In addition, the normal behaviour of motor units (MU) during these contractions also remains elusive. PURPOSE: This study was designed (i) to determine decomposition-based quantitative electromyography (DQEMG), could detect changes in motor unit firing statistics that accompany fatigue in the brachioradialis (BR) and extensor carpi radialis (ECR) muscles over the first 90 seconds of sustained, low-level isometric contractions, (ii) to determine if time-dependent changes in surface EMG parameters are correlated with changes in MU firing rates, and (iii) to determine if time-dependant changes seen in the MU firing characteristics are repeatable within individuals. METHODS: Changes in mean MU firing rates were investigated in the BR (n=1 0) and ECR (n=10) muscles in healthy volunteers (mean age = 28.6 yr, SD ± 3.9) during constant-torque isometric contractions held until exhaustion. Three BR contractions were sustained at 25% of the maximum voluntary contraction (MVC) and two ECR contractions were sustained at 20% MVC. Mean MU firing rates were estimated following the decomposition of 30-second EMG data windows. Time dependant changes in firing rates were investigated using an analysis of variance with time (first, second and third 30 second epochs) included as a main effect. Pearson product-moment correlation coefficients were computed to determine if changes in MU firing rates were related to changes in surface EMG amplitude and frequency parameters (α=0.05). Intra-class correlation coefficients (ICC) were used to determine the within-subject repeatability of the MU firing rate changes, and SEMG parameters. RESULTS: Mean MU firing rate decreased within the first 90 seconds in both muscle groups, and was repeatable across trials using the DQEMG method. Significant correlations between changes in mean firing rates and surface EMG amplitude and frequency content were found in the ECR muscle but not the BR muscle. The reliability of firing rate changes within subjects was moderate in both the ECR (ICC=0.72) and BR muscles (ICC=0.59). The SEMG mean power frequency significantly decreased over contraction time in the ECR muscle, and was found to be a highly reliable measure in both muscles (ICC=0.99 and 0.98, respectively). CONCLUSIONS: Changes in MU characteristics were observed as early as 90 seconds into a low level contraction. Differences found between the two muscles may be due to contraction level or fiber type distributions.

Within-subject reliability of motor unit number estimates and quantitative motor unit analysis in a distal and proximal upper limb muscle

Objective To establish within-subject reliability of motor unit number estimates (MUNEs) and quantitative MU analysis using decomposition-based quantitative electromyography (DQEMG). Methods Following the acquisition of a maximum M-wave, needle and surface-detected EMG signals were collected during contractions of the first dorsal interrosseous (FDI) and biceps brachii (BB). DQEMG was used to extract motor unit potential (MUP) trains and surface-detected MUPs associated with each train, the mean size of which was divided into the maximum M-wave to obtain a MUNE. Retests were performed following the initial test to evaluate reliability. Results Subjects test-retest MUNEs were highly correlated ( r=0.72 FDI; 0.97 BB) with no significant differences between test and retest MUNE values ( P>0.10). Ninety-five percent confidence intervals were calculated to establish the range of expected retest MUNE variability and were ±41 MUs for the FDI and BB. Quantitative information pertaining to MU size, complexity and firing rate were similar for both tests. Conclusion MUNEs and quantitative MU data can be obtained reliably from the BB and FDI using DQEMG in individual subjects. Significance Establishing within-subject reliability of MUNEs and quantitative MU analysis allow clinicians to longitudinally follow changes in the MU pool of individuals with disorders of the central or peripheral nervous system in addition to assessing their response to treatments.

Decomposition‐based quantitative electromyography: Effect of force on motor unit potentials and motor unit number estimates

Decomposition-based quantitative electromyography (DQEMG) allows for the collection of motor unit potentials (MUPs) over a broad range of force levels. Given the size principle of motor unit recruitment, it may be necessary to control for force when using DQEMG for the purpose of deriving a motor unit number estimate (MUNE). Therefore, this study was performed to examine the effect of force on the physiological characteristics of concentric needle- and surface-detected MUPs and the subsequent impact on MUNEs obtained from the first dorsal interosseous (FDI) muscle sampled using DQEMG. Maximum M waves were elicited in 10 subjects with supramaximal stimulation of the ulnar nerve at the wrist. Intramuscular and surface-detected EMG signals were collected simultaneously during 30-s voluntary isometric contractions performed at specific percentages of maximal voluntary contraction (MVC). Decomposition algorithms were used to identify needle-detected MUPs and their individual MU firing times. These MU firing times were used as triggers to extract their corresponding surface-detected MUPs (S-MUPs) using spike-triggered averaging. A mean S-MUP was then calculated, the size of which was divided into the maximum M-wave size to derive a MUNE. Increased levels of contraction had a significant effect on needle- and surface-detected MUP size, firing rate, and MUNE. These results suggest that force level is an important factor to consider when performing quantitative EMG, including MUNEs with this method.