Examination of body static rotation related to step length asymmetry: biomechanics of the thorax and pelvis.

[Purpose] This study determined whether the results of the mobility assessment of pelvic and thoracic rotation (static evaluation), which is often used in clinical settings, are related to step length asymmetry. Moreover, we identified the postural evaluation of rotation that may be related to gait asymmetry. [Participants and Methods] We hypothesize that a certain relationship exists between the static assessments of pelvic rotation and step length asymmetry. Fifteen healthy adult males participated in static posture and gait motion analyses using a motion-capture system. The static evaluation was analyzed using three parameters: pelvic rotation in standing, pelvic rotation with kneeling, and thorax rotation in sitting. [Results] The relationship between the asymmetric variables obtained from static evaluation and gait observations demonstrated a significant correlation. The asymmetric variables of step length and asymmetric variables of thorax rotation in sitting showed a significant relationship. Furthermore, significant correlations were found between asymmetric variables of pelvic rotation during gait and asymmetric variables of step length and between asymmetric variables of pelvic rotation during gait and asymmetric variables of thorax rotation in sitting. [Conclusion] This study revealed asymmetric relationships between thorax rotation in sitting test and step length asymmetry in the gait. Asymmetry in the thorax rotation in sitting may be caused by a gait with biased pelvic rotation.

The apex angle of the rocker sole affects the posture and gait stability of healthy individuals.

BACKGROUND: Rocker sole (RS) shoes have been linked to impaired postural control. However, which features of RS design affect balance is unclear. RESEARCH QUESTION: Which RS design features affect standing balance and gait stability? METHODS: This study utilized an intervention and cross-over design. Twenty healthy young adults (10 males and 10 females) participated in this study. Standing balance and gait stability were measured using a single force platform and three-dimensional motion analysis system, respectively. The experimental conditions included the control shoe and five RS shoes in the combination of apex position (%) and apex angle (degree) for RS50-95, RS60-95, RS70-95, RS60-70, and RS60-110. The main outcome measures were the area surrounding the maximal rectangular amplitude, mean path length, average displacement of the center of pressure along the lateral and anterior/posterior directions, and maximal center of pressure excursion as the standing balance and lateral margin of stability as the gait stability. Statistical analyses were conducted using a two-way split-plot analysis of variance with repeated measures (with RS design as the within-subject factor and sex as the between-subject factor) and the Bonferroni post hoc test (α = .05). RESULTS: Regarding the mean path length, RS60-70 was significantly longer than the control shoe, and it showed a significantly increased lateral margin of stability. Thus, RS60-70 was shown to affect standing balance, limit of stability, and gait stability of the frontal plane during gait. SIGNIFICANCE: These results suggest that the apex angle of the RS design feature affects standing balance and gait stability, and RS60-70 is detrimental to stability. Therefore, when RS with a small apex angle is prescribed, it is necessary to consider the patient's balance ability.

The Effects of Vibratory Frequency and Temporal Interval on Tactile Apparent Motion.

Vibrotactile stimuli can be used to generate the haptic sensation of a static object or the motion of a dynamic object. Here, in this article, we investigated the effects of vibratory frequency and temporal interval on tactile apparent motion. In the experiment, we examined the effect of vibratory frequency with different temporal intervals on tactile apparent motion that results from two successive tactile stimuli on the index fingerpad. Results indicated that tactile apparent motion was perceived not only when both stimuli were either "flutter" or "vibration" stimuli, but also when one of each type was used. Specifically, when the first stimulus was introduced at 40Hz, "continuous motion" was viewed at all combinations of stimulus frequency, and "continuous motion" was clearly noted at the high-frequency combination instead of the low-frequency combination. Also, tactile apparent motion was predominantly viewed in the SOA range of 105 ms to 125 ms. We anticipate that our findings and further research will be essential resources for the design of tactile devices to represent the motion of dynamic objects.

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.

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.

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.

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.