Centro de Engenharia Biomedica / CITE

Rectification of EMG signals is a common processing step used when performing electroencephalographic-electromyographic (EEG-EMG) coherence and EMG-EMG coherence. It is well known, however, that EMG rectification alters the power spectrum of the recorded EMG signal (interference EMG). The purpose of this study was to determine whether rectification of the EMG signal influences the capability of capturing the oscillatory input to a single EMG signal and the common oscillations between two EMG signals. Several EMG signals were reconstructed from experimentally recorded EMG signals from the surface of the first dorsal interosseus muscle and were manipulated to have an oscillatory input or common input (for pairs of reconstructed EMG signals) at various frequency bands (in Hz: 0-12, 12-30, 30-50, 50-100, 100-150, 150-200, 200-250, 250-300, and 300-400), one at a time. The absolute integral and normalized integral of power, peak power, and peak coherence (for pairs of EMG signals) were quantified from each frequency band. The power spectrum of the interference EMG accurately detected the changes to the oscillatory input to the reconstructed EMG signal, whereas the power spectrum of the rectified EMG did not. Similarly, the EMG-EMG coherence between two interference EMG signals accurately detected the common input to the pairs of reconstructed EMG signals, whereas the EMG-EMG coherence between two rectified EMG signals did not. The frequency band from 12 to 30 Hz in the power spectrum of the rectified EMG and the EMG-EMG coherence between two rectified signals was influenced by the input from 100 to 150 Hz but not from the input from 12 to 30 Hz. The study concludes that the power spectrum of the EMG and EMG-EMG coherence should be performed on interference EMG signals and not on rectified EMG signals because rectification impairs the identification of the oscillatory input to a single EMG signal and the common oscillatory input between two EMG signals.

In martial arts and contact sports strikes are performed at near maximum speeds. For that reason, electromyography (EMG) analysis of such movements is non-trivial. This paper has three main goals: firstly, to investigate the differences in the EMG activity of muscles during strikes performed with and without impacts; secondly, to assess the advantages of using Sum of Significant Power (SSP) values instead of root mean square (rms) values when analyzing EMG data; and lastly to introduce a new method of calculating median frequency values using wavelet transforms (WMDF). EMG data of the deltoid anterior (DA), triceps brachii (TB) and brachioradialis (BR) muscles were collected from eight Kung Fu practitioners during strikes performed with and without impacts. SSP results indicated significant higher muscle activity (p = 0.023) for the strikes with impact. WMDF results, on the other hand, indicated significant lower values (p = 0. 007) for the strikes with impact. SSP results presented...

Almost all cultures have roots in some sort of self defence system and yet there is relatively little research in this area, outside of a sports related environment. This project investigated different applications of strikes from Kung Fu practitioners that have not been addressed before in the literature. Punch and palm strikes were directly compared from different heights and distances, with the use of a load cell, accelerometers, and high speed video. The data indicated that the arm accelerations of both strikes were similar, although the force and resulting acceleration of the target were significantly greater for the palm strikes. Additionally, the relative height at which the strike was delivered was also investigated. The overall conclusion is that the palm strike is a more effective strike for transferring force to an object. It can also be concluded that an attack to the chest would be ideal for maximizing impact force and moving an opponent off balance. Key PointsIt has be...

A biomecanica e a ciencia que estuda e quantifica o movimento humano, utilizando os princıpios da mecanica. Sua aplicacao em artes marciais ainda e pouco frequente, especialmente para movimentos de Kung-Fu. O presente trabalho propoe um modelo para determinar o deslocamento da mao em funcao do tempo em um golpe de Kung-Fu. Para validar o modelo, tres indivıduos tiveram seus golpes filmados por uma camera rapida com uma taxa de 1000 Hz. A importancia do uso de velocidades e aceleracoes instantaneas no estudo de movimentos fica muito bem evidenciada no presente trabalho que mostra a aplicacao desses conceitos em um assunto que normalmente ´e de grande interesse dos alunos em geral. Os resultados confirmam a hipotese de que a forca muscular resultante de um movimento de Kung-Fu Yau-Man e constante antes do impacto e mostram como diferentes analises dos mesmos dados podem implicar em resultados distintos.

Background/Study Context: The aging process is associated with a decline
in muscle mass, strength, and conditioning. Two training methods that
may be useful to improvemuscle function are Pilates and proprioceptive
neuromuscular facilitation (PNF). Thus, the present study aimed to compare
the influence of training programs using Pilates and PNF methods
with elderly women.
Methods: Sixty healthy elderly women were randomly divided into three
groups: Pilates group, PNF group, and control group. Pilates and PNF
groups underwent 1-month training programs with Pilates and PNF
methods, respectively. The control group received no intervention during
the 1 month. Themaximal isometric force levels from knee extension and
flexion, as well as the electromyography (EMG) signals from quadriceps
and biceps femoris, were recorded before and after the 1-month intervention
period.
Results: A two-way analysis of variance revealed that the Pilates and PNF
methods induced similar strength gains from knee flexors and extensors,
but Pilates exhibited greater low-gamma drive (i.e., oscillations in
30–60 Hz) in the EMG power spectrum after the training period.
Conclusions: These results support use of both Pilates and PNF methods
to enhance lower limb muscle strength in older groups, which is
very important for gait, postural stability, and performance of daily
life activities.

Almost all cultures have roots in some sort of self defence system and yet there is relatively little research in this area, outside of a sports related environment. This project investigated different applications of strikes from Kung Fu practitioners that have not been addressed before in the literature. Punch and palm strikes were directly compared from different heights and distances , with the use of a load cell, accelerometers, and high speed video. The data indicated that the arm accelerations of both strikes were similar, although the force and resulting acceleration of the target were significantly greater for the palm strikes. Additionally, the relative height at which the strike was delivered was also investigated. The overall conclusion is that the palm strike is a more effective strike for transferring force to an object. It can also be concluded that an attack to the chest would be ideal for maximizing impact force and moving an opponent off balance.

reply: The surface EMG signal is typically a recording of many motor unit action potentials from a muscle. Despite the fact that it is a crude representation of the organization of individual motor unit action potentials, we agree with Halliday and Farmer (2010) that it may contain important information related to motor unit timing. The issue is whether one can accurately extract such information from the interference (raw) or the rectified EMG signal to better understand motor control.

Motor unit timing, however, is a broad term. Studies from single motor units provide at least the following three distinct timing-related sets of information (frequency bands). 1) The average motor unit discharge rate (6–12 Hz). 2) The modulation of motor unit discharge from 0 to 1 Hz (Christou et al. 2007; DeLuca 1982), which likely reflects synaptic noise (Matthews 1996). 3) The modulation of motor unit discharge from 13 to 30 Hz (Christou et al. 2007; Farmer et al. 1993), which has been associated with motor unit synchrony (Christou et al. 2007; Farmer et al. 1993). Subsequently, the following question arises: Which motor unit timing information are we trying to extract from the surface EMG signal? There is evidence that both the interference and rectified EMG signals can identify the mean discharge rate using simple simulations (Myers et al. 2003; see also Fig. 1). During more realistic simulations, however, the rectified EMG impairs the identification of the mean motor unit discharge rate (see Fig. 4 from Farina et al. 2004). There is no evidence that we can extract the 0–1 Hz from either the interference or rectified EMG signal. Finally, although there is evidence for peaks from 13 to 30 Hz in the rectified and interference EMG signals, the origins of such peaks remain unclear. Nonetheless, there is evidence that such peaks from the rectified and interference EMG signals are modulated differently with voluntary effort (Neto et al. 2010)....