Characteristics of Lower Limb Muscle Activity in Elderly Persons After Ergometric Exercise.

This study examined the characteristics of lower limb muscle activity in elderly persons after ergometric pedaling exercise for 1 month. To determine the effect of the exercise, surface electromyography (SEMG) of lower limb muscles was subjected to Daubechies-4 wavelet transformation, and mean wavelet coefficients were compared with the pre-exercise coefficients and the post-exercise coefficients in each wavelet level. The characteristics of muscle activity after pedaling exercise were also compared between the elderly subjects and young subjects. For the elderly subjects, the mean wavelet coefficients were significantly decreased in the tibialis anterior and the gastrocnemius medialis at wavelet levels of 3, 4, and 5 (125-62.5, 62.5-31.25, and 31.25-15.625 Hz, respectively), by pedaling exercise. However, the mean power of wavelet levels of 2 and 3 (250-125 and 125-62.5 Hz) within the rectus femoris and the biceps femoris were significantly increased in the young subjects. The effect of pedaling exercise is different from the effects of heavy-resistance training. It was suggested that the muscle coordination, motor unit (MU) firing frequency, and firing fiber type of lower limb muscles are changed with the different characteristics between elderly and young persons by pedaling exercise for 1 month.

Histological skeletal muscle damage and surface EMG relationships following eccentric contractions.

This study examined the effects of a different number of eccentric contractions (ECs) on histological characteristics, surface electromyogram (EMG) parameters (integral EMG, iEMG; muscle fiber conduction velocity, MFCV; and action potential waveform), and isometric peak torque using the rat EC model. Male Wistar rats (n = 40) were anesthetized, and ECs were initiated in the tibialis anterior muscle via electrical stimulation while the muscle was being stretched by electromotor. The rats were grouped according to the number of ECs (EC1, EC5, EC10, EC20, EC30, EC40, and EC100). Three days after the ECs, surface EMG signals and isometric peak torque were measured during evoked twitch contractions via electrical stimulation of the peroneal nerve. The muscle damage was evaluated from hematoxylin-eosin (HE) stained cross sections as a relative number of damaged fibers to intact fibers. Intense histological muscle damage (approximately 50% to 70% of the fiber), loss of isometric peak torque, disturbance of action potential waveform, and depression of iEMG (approximately -60% to -70%) were observed at EC20, EC30, EC40, and EC100. On the other hand, the MFCV did not change in any EC group. Although muscle damage and pathological surface EMG signals were not found at EC10, isometric peak torque was reduced significantly. In conclusion, the extent of histological muscle damage is not proportionally related to the number of ECs. Muscle damage was reflected by iEMG and action potential waveforms, but not by MFCV, which remained unaffected even though approximately 50% to 70% of the fiber demonstrated injury.

Coordination of the upper-limb segments in physiological tremor with various external loads.

BACKGROUND: This study investigates coordination of the upper-limb segments with various external loads by frequency-domain analysis of physiological tremor during the maintenance of limb posture. Physiological tremor is an involuntary oscillation in every segment of a healthy human. MATERIAL/METHODS: A subject raised his right upper limb forward while extending his hand and fingers. Physiological tremor was measured by acceleration sensors attached to four segments: the index finger, hand, forearm, and upper arm. A balloon filled with helium gas was attached to the forearm as a minus-load condition. A weight band was attached as a plus-load condition. The measured signals were evaluated by frequency-domain analysis: power spectrum and coherence spectrum. RESULTS: The amplitude of upper-limb tremor measured from the four segments decreased with the minus-load and increased with the plus-load. However, the degree of the variation depended on the segment. The amplitude of upper-limb tremor measured from the forearm and the hand decreased remarkably with the minus-load, while the amplitude from the upper arm increased with the plus-load. Although adjacent segments were well coordinated, coordination between the segments varied depending on the external load. The minus-load at the forearm led to a lack of coordination between the upper arm and the forearm. To compensate for this, the movements of the forearm and the hand became coordinated. CONCLUSIONS: The experimental protocol of this study allowed implementing a method to estimate the physiological modification of the neuromuscular system under a hypo-gravitational environment.

Effect of skin temperature on RMS amplitude of electromyogram and mechanomyogram during voluntary isometric contraction.

The aim of this study is mainly to elucidate the relation between the modification of skin temperature and MMG signal properties depending on the contractile force. Ten healthy male volunteers, aged 22.8 +/- 0.7 (mean+/-SE) years, participated in this study. EMG and MMG signals were recorded during voluntary isometric contraction (20, 40, 60, and 80% MVC) of biceps brachii muscle under a skin temperature of 34 degrees C (control), 28 degrees C (cooling), and 40 degrees C (heating), respectively. A significant difference of MVC during elbow flexion was not recognized among the thermal conditions. Root mean square values of EMG and MMG (i.e., rms-EMG and rms-MMG) increased depending on the contractile level (P< 0.01). In the heating condition, the rms-MMG progressively increased in response to an increase of up to 60% MVC, however, it was nearly unchanged at a contractile force higher than 60% MVC The rms-EMG was not significantly influenced by the skin temperature. The rms-MMG significantly increased depending on the skin temperature at each contractile level (P< 0.01). There were significant interactions between contractile force and skin temperature for rms-MMG (P< 0.01). In conclusion, by modification of passive muscle temperature, rms-MMG was significantly altered in comparison with MVC and rms-EMG, which might be reflective of the changes of the mechanical contractile properties of muscle fibers.

Comparison of experimental and numerical muscle fiber conduction velocity (MFCV) distribution around the end-plate zone and fiber endings.

BACKGROUND: The distribution of muscle fiber conduction velocity (MFCV) estimated from surface myoelectric signals differs depending on the recording electrode locations. It is assumed in this study that the irregular values of MFCV may be estimated around the end-plate zone and the fiber endings due to effect of unique interference property of myoelectric signals, and its hypothesis is confirmed experimentally and numerically in consideration of the waveform characteristics of surface myoelectric signals. MATERIAL/METHODS: In experimental study, the surface myoelectric signals are recorded by array electrodes during voluntary isometric contraction in biceps brachii muscle. In the numerical study, the surface myoelectric signals in consideration of the interference property of some motor unit activities are calculated from the current dipole model which simulated the firing features of muscle fiber from end-plate zone to fiber endings. MFCV is estimated by the technique of cross-correlation. Maximum correlation coefficient (Rxy(Ts)) and amplitude ratio (AMPratio) are used to evaluate similarity and attenuation rate between traveling signals. RESULTS: In both results of experimental and numerical studies, the MFCV significantly increase when both Rxy (Ts) and AMPratio decrease around the end-plate zone and fiber endings although three parameters denote constant values in the locations other than the end-plate zone and the fiber endings. The high correlativity is recognized between the experimental and numerical data for MFCV, Rxy (Ts), and AMPratio. CONCLUSIONS: Therefore, it is demonstrated by experimental and theoretical studies that MFCV, Rxy(Ts), and AMPratio are influenced by irregular waveform properties depending on both positions of the end-plate and fiber endings.

Neuromuscular control of physiological tremor during elastic load.

BACKGROUND: Physiological tremor is an involuntary and continuous oscillation in every limb segment of a healthy human. This study investigates the neuromuscular control of physiological tremor by an elastic load applied to the middle finger. MATERIAL/METHODS: The subject maintained a stretching position of the middle finger against various tension springs. Physiological tremor was detected by an acceleration sensor attached to the middle finger. The motor-unit activity was estimated by surface electromyogram (EMG) measured from the extensor digitorum communis muscle with physiological tremor. The tremor and the EMG signals were analyzed by power and coherence spectra. RESULTS: Three frequency components appeared in physiological tremor while the subject extended the middle finger against the tension spring. They were classified as two load-independent components and a load-dependent component. Although the motor-unit activity was enhanced by the extension of the middle finger against a stiffer spring, the tremor amplitude did not significantly change. The extensor digitorum communis muscle produced a larger contraction force to maintain the finger posture against a stiffer spring, while the stiffness of the tension spring restrained the finger movement. The three frequency components of physiological tremor correlated with the motor-unit activity. These results supported the hypothesis of the origin of physiological tremor. The stretch-reflex system caused the load-dependent component, and the mechanical property of the elastic load determined its frequency. The supraspinal system produced the two load-independent components. CONCLUSIONS: The neuromuscular control to maintain the stretching of the middle finger against the elastic load gave rise to the three frequency components in physiological tremor.

Psychophysiological evaluation of simulator sickness evoked by a graphic simulator.

The present study investigated the effects of simulator sickness, as an important bias factor on evaluation of emotional changes under the controlled condition of driving a car for 60 min at a constant speed (60 km/h) in a graphic simulator. Simulator sickness was measured and analyzed every 5 min using both subjective evaluation and physiological signals. Results of the subjective evaluation showed there was a significant difference between the rest and the driving conditions 10 min after the main experiment started and that the level of difference increased linearly with time. Analysis of the central and the autonomic nervous systems showed the significant differences in delta, theta, alpha and beta bands of an electroencephalogram (EEG), skin temperature, and the R-R interval between the rest and the driving conditions after about 5 min from the start of driving. In particular, there was the highest correlation between parameter of theta and subjective evaluation, and thus theta was considered an effective physiological parameter for numerically evaluating simulator sickness. The results indicate that physiological changes due to simulator sickness can be a bias factor in evaluation of human sensibility.

Analysis of mutual information content for EEG responses to odor stimulation for subjects classified by occupation.

To investigate the changes of cortico-cortical connectivity during odor stimulation of subjects classified by occupation, the mutual information content of EEGs was examined for general workers, perfume salespersons and professional perfume researchers. Analysis of the averaged-cross mutual information content (A-CMI) from the EEGs revealed that among the professional perfume researchers changes in the A-CMI values during odor stimulation were more apparent in the frontal region of the brain, while for the general workers and perfume salespersons such changes were more conspicuous in the overall posterior temporal, parietal and frontal regions. These results indicate that the brains of professional perfume researchers respond to odors mainly in the frontal region, reflecting the function of the orbitofrontal cortex (OFC) due to the occupational requirement of these subjects to discriminate or identify odors. During odor stimulation, the perfume salespersons, although relatively more exposed to odors than the general workers, showed similar changes to the general workers. The A-CMI value is in inverse proportion to psychological preferences of the professional perfume researchers and perfume salespersons, though this is not the case with the general workers. This result suggests that functional coupling for people who are occupationally exposed to odors may be related to psychological preference.

The origins of physiological tremor as deduced from immersions of the finger in various liquids.

To investigate the influence of gravity on physiological tremor during a holding stretch of the finger, tremor during immersion of the finger in liquids was measured. Liquids with various densities and various coefficients of viscosity were used. Tremor was detected using an acceleration sensor, and power spectrum analysis was performed on the acceleration signal of the tremor. The total power of the tremor spectrum decreased with an increase of the density and an increase of the coefficient of viscosity, the high frequency domain of the tremor spectrum showing a larger decrease than the low frequency domain. Linear regression analysis showed that the viscosity of the liquid had a larger effect on tremor than the buoyancy due to the liquid. A model was proposed for tremor during immersion of the finger in liquid. The effect of the buoyancy and the viscosity on tremor was examined using the proposed model. The origin of two frequency bands in the tremor spectrum was verified by both the immersion experiment and the proposed model. The stretch-reflex system via the spinal cord produced a high frequency band around 25 Hz, while the supraspinal system caused a low frequency band around 10 Hz. The neuromuscular function of the human body was evaluated using the amplitude and the frequency of tremor.