Neuromuscular electrical stimulation (NMES) is a common tool that is used in clinical and laboratory experiments and can be combined with mechanomyography (MMG) for biofeedback in neuroprostheses. However, it is not clear if the electrical current applied to neuromuscular tissues influences the MMG signal in submaximal contractions. The objective of this study is to investigate whether the electrical stimulation frequency influences the mechanomyographic frequency response of the rectus femoris muscle during submaximal contractions. Thirteen male participants performed three maximal voluntary isometric contractions (MVIC) recorded in isometric conditions to determine the maximal force of knee extensors. This was followed by the application of nine modulated NMES frequencies (20, 25, 30, 35, 40, 45, 50, 75, and 100 Hz) to evoke 5% MVIC. Muscle behavior was monitored by the analysis of MMG signals, which were decomposed into frequency bands by using a Cauchy wavelet transform. For each applied electrical stimulus frequency, the mean MMG spectral/frequency response was estimated for each axis (X, Y, and Z axes) of the MMG sensor with the values of the frequency bands used as weights (weighted mean). Only with respect to the Z (perpendicular) axis of the MMG signal, the stimulus frequency of 20 Hz did not exhibit any difference with the weighted mean (P = 0.666). For the frequencies of 20 and 25 Hz, the MMG signal displayed the bands between 12 and 16 Hz in the three axes (P < 0.050). In the frequencies from 30 to 100 Hz, the muscle presented a higher concentration of the MMG signal between the 22 and 29 Hz bands for the X and Z axes, and between 16 and 34 Hz bands for the Y axis (P < 0.050 for all cases). We observed that MMG signals are not dependent on the applied NMES frequency, because their frequency contents tend to mainly remain between the 20- and 25-Hz bands. Hence, NMES does not interfere with the use of MMG in neuroprosthesis.
Knowledge of the fatigue process in karate sport is essential to improve the performance of top athletes. The physiological and biomechanical behavior during the Karate Specific Aerobic Test (KSAT) fatigue protocol in karate was investigated. PCR, lactate, glucose and cortisol were collected before and after the fatigue protocol application in karate, besides that, and heart rate and technical speed were measured. The results indicated increase in C protein reactive (60%), creatine kinase (25%), cortisol (30%), lactate dehydrogenase (90.9%) and decrease in glucose (21.2%). The maximum speed was: in kizami zuki, 5.75 ± 0.31 m/s; in mawashi geri, 9.0 ± 0.24 m/s, in gyako zuki, 7.23 ± 0.54 m/s and in kizami mawashi geri, 6 ± 0.34 m/s. The mean time for each set was 2.99 ± 0.17 s. There was reduction in speed and duration of set for all techniques, especially in the final sets (p<0.05), indicating the presence of fatigue. Gyako zuki was the main blow affected by the phenomenon (p<0.05). Also, the high values observed in biochemical variables after the protocol application indicate metabolic fatigue with muscle damage. Therefore, the athlete adapted his motor behavior in order to hold his technical speed.
Background Improving balance control in older adults is one of the main objectives of fall prevention programs, and tennis could represent a promising way to train balance control. Objective To verify whether older tennis players have similar reactive response characteristics to balance perturbations to those of healthy young people. Methods Fifteen young people (23.00 ± 1.96 years) and twelve older people (69.08 ± 3.82 years), remained in an orthostatic position, with their arms at their sides, on a force platform during ten mediolateral perturbations. The surface electromyography signal of the gluteus maximus, tibialis anterior, gastrocnemius lateralis, and vastus lateralis muscles was acquired on the dominant side. Results The velocity and amplitude parameters of the center of pressure displacement were similar between the groups, as well as the amplitude of the electromyography signal of the tibialis anterior, vastus lateralis, and gastrocnemius lateralis muscles. There was a statistical difference between the groups in the gluteus maximus muscle in the first perturbation. Conclusions Older tennis players present similar center of pressure velocity performance and amplitude of center of pressure displacement behavior to young people. Older tennis players have an increased range of muscle activation, generating automatic postural responses adapted to deal with situations of balance perturbations.
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