Roger G. T. Mello

Digital Butterworth filter for subtracting noise from low magnitude surface electromyogram

This work presents a digital filter designed to delimitate the frequency band of surface electromyograms (EMG) and remove the mains noise and its harmonics, focusing the signal analysis during reduced muscle activity. A Butterworth filter was designed as the frequency-domain product of a second order, high-pass filter with cutoff frequency 10 Hz, an eighth order low-pass filter, with cutoff at 400 Hz and six stop-band filters, second order, centered at the 60 Hz mains noise and its harmonics until 360 Hz. The resulting filter was applied in both direct and reverse directions of the signals to avoid phase distortions. The performance was evaluated with a simulated EMG signal with additive noise in multiples of 60 Hz. A qualitative assessment was made with real EMG data, acquired from 16 subjects, with age from 20 to 32 years. Subjects were positioned in orthostatic position during 21s, being only the last second analyzed to assure stationarity. EMG were collected by Ag/AgCl electrodes on right lateral gastrocnemius, amplified with gain 5000, filtered in the band from 10 Hz to 1 kHz, and thus digitized with 2ksamples/s. The filter effectively removed the mains noise components, with attenuations greater than 96.6%. The attenuation of the simulated signal at frequencies below 15 Hz and at 60 Hz caused only a small reduction of total power, preserving the original spectrum. Thus, the filter resulted suitable to the proposed application.

Detection of the anaerobic threshold by surface electromyography.

This work aims at presenting a method for automatic detection of the anaerobic thresholds by surface electromyography (RMS-slope) and compare with respective values identified by the analysis of ventilatory gas exchange. Thirteen healthy adults were submitted to a single maximal oxygen uptake test, being monitored the ventilatory parameters VO2 , VCO2, and VE, and the surface EMG (SEMG) of the right vastus lateralis muscle. Each cycle of myoelectric activity was automatically detected and the time series of the mean RMS values of these cycles used for determining the SEMG threshold (SEMG-T) by linear regression. The method was successful to determine SEMG-T for all subjects, with consistent results when compared to respective anaerobic thresholds visually estimated in the ventilatory equivalent VE/VO2

Is the firing rate of motor units in different vastus medialis regions modulated similarly during isometric contractions

Introduction: Previous evidence suggests the fibers of different motor units reside within distinct vastus medialis (VM) regions. It remains unknown whether the activity of these motor units may be modulated differently. Herein we assess the discharge rate of motor units detected proximodistally from the VM to address this issue. Methods: Surface electromyograms (EMGs) were recorded proximally and distally from the VM while 10 healthy subjects performed isometric contractions. Single motor units were decomposed from surface EMGs. The smoothed discharge rates of motor units identified from the same and from different VM regions were then cross‐correlated. Results: During low‐level contractions, the discharge rate varied more similarly for distal (cross‐correlation peak; interquartile interval: 0.27–0.40) and proximal (0.28–0.52) than for proximodistal pairs of VM motor units (0.20–0.33; P = 0.006). Discussion: The discharge rates of motor units from different proximodistal VM regions show less similarity in their variations than those of pairs of units either distally or proximally. Muscle Nerve 57: 279–286, 2018

Lumbar multifidus and erector spinae electromyograms during back bridge exercise in time and frequency domains.

BACKGROUND Muscle activity is studied during trunk stabilization exercises using electromyograms (EMG) in time domain. However, the frequency domain analysis provides information that would be important to understand fatigue process. OBJECTIVE To assess EMG of lumbar multifidus (LM) and erector spinae (ES) muscles, in time and frequency domains, during back bridge exercise. METHODS Nineteen healthy young men performed the exercise for one minute and EMG was monitored by surface electromyography. Normalized root mean square (RMS) value and spectral median frequency (MF) were compared between beginning and final epochs of test. The dynamics of the MF during whole test was also obtained by short-time Fourier transform. RESULTS RMS values were about 30% of maximum voluntary contraction, and LM muscle showed greater MF than ES, which did not decrease at the final of exercise. However, the slope of MF was significant mainly for LM. CONCLUSIONS Muscle activation of 30% is sufficient to keep lumbar stability and is suitable to improve muscular endurance. The significance of MF slope without decreasing at the final of exercise indicates challenging muscular endurance without imply on high fatigability. Due to lower muscular demand, this exercise might be recommended for trunk stabilizing for low back pain patients.

Effects of maximal oxygen uptake test and prolonged cycle ergometer exercise on sway density plot of postural control

This work aims at testing the influence of the maximal oxygen uptake test and prolonged cycle ergometer exercise on sway density plot (SDP) parameters of postural control. Sixteen healthy male subjects were submitted to stabilometric tests with eye open and closed, before and after two different exercises. The maximal oxygen uptake test caused decrease of the mean duration of peaks in SDP, decreasing the stability level, without modify the rates of central and muscular torque controls. Conversely, 60 min exercise increased the mean time interval between two consecutive peaks in SDP, thus decreasing the control rate but not changing the stability level. Visual privation had a greater effect on body sway than these exercises, which were applied to muscles that are not the main actuators in body sway control. Concluding, the changes in postural control are dependent on the intensity and duration of exercise.

Heart Rate Variability Indexes in Dementia: A Systematic Review with a Quantitative Analysis

BACKGROUND Decreased heart rate variability (HRV) indexes indicate low vagal activity and may be associated with development of dementia. The neurodegenerative process is associated with the cardiovascular autonomic control. OBJECTIVE The aim of this systematic review was to investigate the effect size (ES) magnitude of the HRV indexes in the evaluation of autonomic dysfunction in older persons with dementia. METHODS PubMed (Medline), Web of Science, Scopus, Scielo, Lilacs, and APA Psycnet were consulted. Complete original articles published in English or Portuguese, investigating the association between autonomic dysfunction and dementia, using the HRV indexes were included. RESULTS The search identified 97 potentially relevant articles. After screening the full text, eight articles were included in the qualitative analysis and six were included in the quantitative analysis. Almost all indexes showed a negative ES for all types of dementia and mild cognitive impairment. The most common frequency band of the power spectrum density function was the high frequency, which was reported by six studies. The meta-analysis of high frequency power in Alzheimers disease group showed high heterogeneity and inconsistent results. CONCLUSION The negative effect size suggests an autonomic dysfunction in all types of dementia as well as mild cognitive impairment. However, further analysis is necessary to support these results.

Role of vestibular sensor on body sway control: Coherence between head acceleration and stabilogram

This work aims at evaluating the role of the vestibular system in the postural sway control using the coherence function. A sample of 19 young, healthy male adults was monitored with a three axial accelerometer placed over the head during a stabilometric test, standing on a force platform during 3 min in four conditions: eyes closed and open, and feet apart and together. The magnitude squared coherence (MSC) function and Monte Carlo simulation was used to correlate changes in body sway with head accelerations. Significant MSC values were found in the frequency range 0.1-0.5 Hz, mainly in conditions of larger oscillations: eyes closed and feet together. These results may be related to utricular otoliths responses and ankle strategy.

Principal components of frequency domain electromyograms for muscular fatigue analysis

The parameters commonly employed for muscular fatigue (MF) analysis, the mean frequency (Fmean) and median frequency (Fmedian) of surface EMG (SEMG) spectra, did not present consistent results for exercises performed at low to moderate intensities. For overcoming this limitation, the present study proposes the use of principal component (PC) analysis of SEMG spectra for MF monitoring. The SEMG from vastus lateralis muscle of 24 young male subjects were recorded during a maximal effort test in cycle ergometer. Epochs of 200 ms SEMG, extracted from each period of muscle activation of each subject were used for estimating the amplitude spectra, which were employed to obtain the first two PCs. The PC coefficients from the first 40 spectra were used as a reference for calculating the standard distance. This index presented a consistent increase along the exercise, while the values of Fmean and Fmedian did not present any pattern. Comparisons between initial and final values from all subjects show no significant changes in Fmean and Fmedian (Student t test, P > 0.05) and a significant increase (P≪10−3) in standard distance, indicating this index as an alternative to MF analysis in cyclical exercises.

Cross-correlation between head acceleration and stabilograms in humans in orthostatic posture

This work aims at evaluating the role of the vestibular system in the postural sway control using the cross correlation function. A sample of 19 young, healthy male adults was monitored with a three axial accelerometer placed over the head during a stabilometric test, standing on a force platform during 3 min in four conditions: eyes closed and open, and feet apart and together. The normalized cross correlation (NCCF) function and the Monte Carlo simulation were used to correlate changes in body sway with head accelerations. Significant NCCF was rarely observed in conditions with opened eyes, and occurred in six subjects with eyes closed and reduced support basis. These results are inconclusive. As no delayed response was observed, the classical negative feedback appears to be absent, and either phasic displacements of the center of pressure and the head or anticipatory control could be occurring.

Crossover assessment of cardiolocomotor synchronization during running

PurposeThis study aimed at testing the hypothesis that positive cardiolocomotor coordination (CLC) measure occurs by chance during a running task where the heart rate (HR) is approximated to the step frequency (StepF).MethodsThe electrocardiogram and electromyogram from the right gastrocnemius lateralis muscle were continuously recorded from ten healthy young men running at a paced rhythm of 152 step/min, to monitor HR and StepF. CLC was evaluated by phase synchrograms and the index of conditional probability (iCP). Results were validated with surrogate data and a crossover approach, where the HR of one subject was related to the StepF of another one, and comparisons were made combining subjects two by two.ResultsSix subjects showed synchrogram structures and high iCP values (≥0.8), suggesting the occurrence of physiological entrainment, when the HR reached the SF range. In crossover analysis, phase synchrograms and iCP presented similar behavior of original data when the HR from one subject was close enough to the SF from another one. Significant iCP values in 46 of 90 comparisons (51%) were observed, including all cases crossing signals among the six positive cases.ConclusionSynchrogram and iCP tools currently employed for measuring CLC are not appropriate because they indicate the occurrence of this phenomenon even among subjects who ran on different days and times of each other.