Fabiano Peruzzo Schwartz

Compression of S-EMG signals by transforms and spectral profile for bit allocation

In this paper, an S-EMG signal encoder based on wavelet transform and bit allocation for sub-bands is presented. Were implemented and compared two methods of allocating bits: linear decreasing spectral profile and hyperbolic tangent decreasing spectral profile. Comparisons with other encoders in the literature are shown. In the development of the encoder, always sought to maximum compression, but without loss of fidelity of the reconstructed signal, a fundamental characteristic of the analysis of electromyographic signals. Developed algorithm showed very satisfactory and promising results.

Relationship between ventilatory threshold and muscle fiber conduction velocity responses in trained cyclists.

The relationship between surface electromyography (SEMG) amplitude and the ventilatory threshold has been extensively studied. However, previous studies of muscle fiber conduction velocity (MFCV) are scarce and present insufficient evidence concerning the relationship between MFCV and metabolic responses during cycling. Based on that fact, the purpose of this study is twofold: (1) to investigate the existence of a MFCV threshold (MFCVT) during cycling and (2) to verify if this possible breakpoint is correlated with the ventilatory threshold (VT) and the SEMG threshold (SEMGT). Eight trained male cyclists (age 36.0±9.7years) performed an incremental cycling test with initial workload of 150W gradually incremented by 20Wmin(-1) until the exhaustion. Gas analyses were conducted using a breath-by-breath open-circuit spirometry and SEMG were registered from vastus lateralis in each pedaling cycle with a linear array of electrodes. A bi-segmental linear regression computer algorithm was used to estimate VT, MFCVT and SEMGT respectively in the carbon dioxide production (VCO2), MFCV and electromyography root mean square (EMG RMS) curves. The one way ANOVA for repeated measures did not reveal any significant difference among VT (77.1±7.5% of VO2max), MFCVT (80.3±10.4% of VO2max) and SEMGT (81.9±11.7% of VO2max). The Bland and Altman procedure confirmed a good concordance between SEMGT and VT (Bias=5.5 of %VO2max) as well as MFCVT and VT (Bias=5.2 of %VO2max). The present findings suggest that muscle fiber conduction velocity threshold is a valid and reliable non-invasive tool to obtain information about ventilatory threshold in trained cyclists.

Análise de Filtros Espaciais em Sinais EMG de Superfície nas Condições do Máximo Volume de Contração

Nowadays the surface EMG measurement and its signal analysis have combined two important techniques in order to improve the signal resolution and better investigate single motor units: measurements configurations with smaller pick-up areas and application of the spatial filtering to electromyography. Smaller pick-up areas can be achieved through multielectrode arrays and multichannel recording, making possible the detection of correlated excitations at different sites of the muscle. Spatial filters combine the information of several electrodes to form one output signal channel. This work aims at evaluating the EMG signals measured from some subjects with a linear array of 16 electrodes and compare their resolution through the application of Bipolar, Longitudinal Double Diferentiating and Longitudinal Quadruple Diferentiating spatial filters.

Isokinetic work-to-surface electromyographic signal energy ratios as a muscular fatigue indicator

Efficiency of muscular work is usually measured as the relationship between work load and maximum exercise duration. The present study analyzes the efficiency feature as a ratio between mechanical work (WK) and the energy (E) of the surface electromyographic signal (SEMG). This relation (WK/ESEMG) was compared with the most common electromyographic descriptors and its behavior was observed during muscle fatigue. A total of sixteen healthy men (26.8 ± 4.7 yrs, 175.7 ± 4.7 cm, and 79.2 ± 9.4 kg) performed three sets of ten maximal concentric repetitions of dominant knee extension at 60º/s on an isokinetic dynamometer, with 1 minute of rest interval between the sets. The SEMG signals were recorded during the exercises. With the view to minimize the factors other than fatigue that also influence the SEMG descriptors behavior, the only isokinetic repetition phase considered for measurements was the load range. Statistical analyses showed significant correlations between WK/ESEMG and the traditional electromyographic fatigue indicators.

Surface EMG and spatial resolution analysis with estimation of electromyographic descriptors

Spatial filtering has become a common way to improve the resolution of surface electromyographic signals (SEMG) when used in connection with electrode arrays. The goal of this study is to observe the behavior of S-EMG amplitude and spectral descriptors when signals are submitted to a longitudinal quadruple differentiating spatial filter. Signals were acquired at 20% and 60% of the maximum voluntary contraction using a linear array of eight surface electrodes in order to understand the impact of the filtering technique in the S-EMG variables during fatiguing and non-fatiguing contractions. The final results show that the filtering procedure yields better selectivity, suggesting that single motor units can be better observed if spatial filters and measurement configurations with smaller pick-up areas are used. During fatiguing contractions, however, further analysis is needed.

Study of muscle fatigue in isokinetic exercise with estimated conduction velocity and traditional electromyographic indicators

INTRODUCTION: In the study of human biomechanics, it is often desirable to evaluate fatigue in the muscles that are involved in performing a particular task. Identifying the phenomena responsible for this condition is a problem that in most cases is complex and requires appropriate research mechanisms. Isokinetic dynamometry (ID) and surface electromyography (SEMG) are two techniques widely used in studies on strength and muscle fatigue. Their effectiveness is conditioned upon a good understanding of their limitations and the adoption of procedures to fully exploit the potential of each one. The main goal of the present study is to verify whether the electromyographic parameters, especially the conduction velocity (CV), are sensitive to the fatigue instauration process within sets of maximal isokinetic contractions. CV is a basic physiological parameter directly related to muscle activity and still little explored in experiments combining ID and SEMG. METHODS: Instrumentation architecture that combines ID and SEMG was used to estimate electromyographic and biomechanical parameters in protocols of maximum intensity isokinetic knee extension exercises. This architecture allows for limiting the parameter estimates to a specific region of isokinetic exercise, called the isokinetic load range (ILR), where one can consider that the angular velocity is constant and the SEMG signals are cyclo-stationary. Electromyographic signals were acquired using an array of electrodes. CONCLUSION: The results suggest that CV and the other SEMG parameters, including amplitude and frequency descriptors, are sensitive to detect a fatigue process only in protocols that restrict the analysis to ILR and that also bring the subject to a state of fatigue quickly.

The behavior of action potential conduction velocity on isokinetic knee extension tests

The present study investigates the behavior of action potential conduction velocity (CV) on each repetition of an isokinetic test set and on each set as a whole. A total of seven healthy men (27.7 ± 2.8 yrs, 1.74 ± 0.06 m, and 79.6 ± 11.0 Kg) performed 3 (three) sets of 10 (ten) maximal concentric repetitions of dominant knee extension at 60°/s on an isokinetic dynamometer, with 1 minute of rest interval between the sets. The surface electromyographic (SEMG) signals were recorded from the vastus lateralis muscle during the exercises. CV was estimated with a spectral matching method which requires the SEMG acquisition technique based on a flexible linear array of electrodes (here used with 8 electrodes and 5 mm inter-electrode distance). With the view to minimize the factors other than fatigue that also influence the CV behavior, only the extension phase of the isokinetic exercise repetition was considered for measurements. Results showed that CV usually increases during a single repetition whereas it has a decreasing tendency along the isokinetic set seen as a whole.

Low-load high-velocity resistance exercises improve strength and functional capacity in diabetic patients

This study investigated the effects of low-load high-velocity resistance exercises on neuromuscular and functional outcomes in patients with Type 2 diabetes (T2D) during the early-phase of resistance training. Thirty participants with T2D performed 18 training sessions (6 weeks – 3x week) in one of two groups: low-load high-velocity exercises (LLHV, n=15, 62.1±10.5 years) or recreational activities (RA, n=15 56.7 ± 19.4 years). LLHV performed resistance exercises with 3x 8reps as fast as possible with 50-60% 1RM. RA performed light activities. Strength, power, and functional tests were assessed. There was significant increasing in the knee extension peak-torque at 60°/s (7.6%) and 180°/s (12.2%), rate of force development in the LLHV group (P<0.05), whereas there were no changes in the RA group. Significant increases in functional test were observed in the LLHV group (P<0.01) with no changes in the RA group. In conclusion, the LLHV induced marked improvements in neuromuscular parameters, as well as in the functional capacity of participants with T2D.

The Influence of Angular Velocity and Fatigue State on the Initial Joint Angle of Each Isokinetic Phase of Knee Extension Tests

Movement artifacts related to exercise on an isokinetic device can lead to misunderstandings regarding data interpretation. The transitions among the movement phases of a dynamometer lever arm usually have unique ocurrences that may confound test data and, thereby, the test conclusions. It is not unusual to have erroneous readings of peak torque measurements that are consequences of velocity overshoot artifact. As the correct analysis of isokinetic tests must consider only the data obtained under constant velocity conditions, this study investigated if the initial joint position of each isokinetic phase varies with the changing of angular velocity and fatigue state. Special attention was given to the range where velocity is considered constant (isokinetic). Results showed that no influence is caused by fatigue. Angular velocity did not produce significant differences on isokinetic range what suggests that its initial joint angle can be used as a reference point for torque estimates.

Fadiga muscular entre séries de exercícios isocinéticos em mulheres jovens

Abstract: OBJECTIVE: To examine the effect of two rest interval (RI) on isokinetic Peak Torque (PT) and total work (TW) produced by young women. METHODS: 17 untrained women (27.2 ± 4.1 yrs; 56.8 ± 6.9 kg; 162.6 ± 7.0 cm) performed three sets of 10 unilateral isokinetic knee extension repetitions at 60° and 180°/s with one and two minutes of RI. Statistical evaluation was performed using a two x three ANOVA [RI (one and two minutes) x set (1 st , 2 nd , 3 rd )] with α < 0.05. RESULTS: One minute was not enough to keep PT and TW between sets (p<0.05) at 60o (reduction of 15.7% in PT and 19.8% in TW) and 180o/s (reduction of 3.6% in PT and 5.6% in TT). Two minutes was enough only at 180o/s. However, two minutes of RI was greater (p<0.05) than one minutes at 60°/s for PT during the 2 nd and 3 rd sets. CONCLUSION: Two minutes is sufficient to keep PT within typical isokinetic resistance training protocols at 180o/s, but not at 60o/s in young women. Keywords: Torque. Muscle fatigue. Knee extension. Isokinetic.