RESUMO
Reciprocal inhibition and coactivation are strategies of the central nervous system used to perform various daily tasks. In automatic postural responses (APR), coactivation is widely investigated in the ankle joint muscles, however reciprocal inhibition, although clear in manipulative motor actions, has not been investigated in the context of APRs. The aim was to identify whether reciprocal inhibition can be observed as a strategy in the recruitment of gastrocnemius Medialis (GM), Soleus (So) and Tibialis Anterior (TA) muscles in low- and high-velocity forward and backward perturbations. We applied two balance perturbations with a low and a high velocity of displacement of the movable platform in forward and backward conditions and we evaluated the magnitude and latency time of TA, GM and So activation latency, measured by electromyography (EMG). In forward perturbations, coactivation of the three muscles was observed, with greater activation amplitude of the GM and lesser amplitude of the So and TA muscles. For backward, the pattern of response observed was activation of the TA muscle, a decrease in the EMG signal, which characterizes reciprocal inhibition of the GM muscle and maintenance of the basal state of the So muscle. This result indicates that backward perturbations are more challenging.
Assuntos
Tornozelo , Eletromiografia , Músculo Esquelético , Equilíbrio Postural , Humanos , Músculo Esquelético/fisiologia , Masculino , Adulto , Tornozelo/fisiologia , Equilíbrio Postural/fisiologia , Adulto Jovem , Feminino , Articulação do Tornozelo/fisiologiaRESUMO
Low back pain (LBP) is a painful manifestation in the lower part of the spine which causes disabilities changing the sensitivity of sensory neurons resulting in weakness of postural muscles interfering with the balance. It is not already clear if LBP people's muscle changes affect the centre of pressure (CoP) recovery in challenging stance perturbations. The aim of this study was to identify differences in the muscle reactions of people with and without LBP to control CoP in challenging stance perturbations. We applied low (Vel1) and high (Vel2) magnitude stance perturbation by a movable platform and evaluated (a) the magnitude and latency time of trunk and lower limb muscle activation, (b) and the displacement and the latency time of the first CoP peak. The latency of trunk and hip muscle activation on Vel2 was lower for LBP group. The CoP latency and displacement did not change between groups and velocities indicating that the muscles took the same time to overcome the external forces. In conclusion, the maintenance of CoP latency at both velocities was not affected on Vel2, suggesting that such alterations have protective action and preservation of the pain on the LPB group in challenging stance perturbations.
Assuntos
Dor Lombar , Fenômenos Biomecânicos , Quadril , Humanos , Músculo Esquelético/fisiologia , Equilíbrio Postural/fisiologiaRESUMO
OBJECTIVES: Challenging quiet standing tasks for the ankle, knee, hip, and neck joints were used to test the effect of pre-cueing on the reaction time of articular stabilization strategies. METHOD: We assessed balance recovery in 15 subjects who were exposed to backward translations on a movable platform during two conditions: alerted, where participants gazed at a countdown light that pre-cued the onset of the platform translation; and unalerted, without onset time pre-cue. RESULTS: We compared the angular variation of the ankle, knee, hip, and neck joints between the two conditions over four window epochs (0-50 ms; 50-100 ms; 100-150 ms; 150-200 ms). When comparing the window epochs of the ankle and hip joints between conditions, a significant effect was observed in the first and second windows. In the second and third windows, a significant effect was only observed in the alerted group, thereby indicating a faster stability for alerted condition. No significant effect was observed for the knee joint, while a significant effect was observed in the neck joint during the third and fourth windows of the alerted condition. CONCLUSIONS: Pre-cueing can modify the synergies of the automatic reactive postural responses, prioritizing the stabilization of main joints such as the ankle and hip over that of the neck and knee. It was suggested that joint stabilization in the hip occurred due to the involuntary anticipation preprogrammed in the cortex by the visual pre-cue.
Assuntos
Tornozelo , Postura , Articulação do Tornozelo , Fenômenos Biomecânicos , Articulação do Quadril , Humanos , Articulações , Joelho , Articulação do Joelho , Equilíbrio PosturalRESUMO
Parkinson's disease (PD) is a progressive neurodegenerative disease, with a worldwide incidence of 1% in individuals >60 years of age. Its primary characteristics include postural impairments and changes in circadian rhythms. The authors investigated the association between postural impairment and changes in circadian rhythms in 24 PD subjects diagnosed with stages 1 to 3 on the Hoehn-Yard (HY) scale and regularly used dopaminergic medication for at least 1 year (experimental group - EG) and 24 healthy elderly individuals without a history of neurological impairment as the control group (CG). Static balance tests using a force plate were performed, and activity/rest rhythm, according to the relative amplitude of L5 and M10 values, was monitored for seven consecutive days using actimetry. The results indicated differences in posturographic indicators of mediolateral displacement (ML) [EG, 4.71 ± 0.85 mm; CG, 2.79 ± 0.53 mm (p < .0001)] and anteroposterior displacement of the center of pressure (COP) [EG, 5.61 ± 2.43 mm; CG, 8.23 ± 1.72 mm (< 0.0001)], ML velocity of the COP [EG, 2.39 ± 0.83 mm/s; CG, 1.40 ± 0.18 mm/s (p < .0001)], and total distance of the COP in the tandem stance condition [EG, 227.6 ± 75 mm; CG, 53.4 ± 6.1 mm (p < .0001)] between the EG and CG. There was no correlation between relative amplitude and posturographic data for the EG. Postural impairments were verified in comparing the EG and CG; however, there was no association between posturographic indicators and activity/rest rhythm.
Assuntos
Doenças Neurodegenerativas , Doença de Parkinson , Idoso , Ritmo Circadiano , Humanos , Equilíbrio PosturalRESUMO
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.