Katsumi Mita

Mechanomyogram and force relationship during voluntary isometric ramp contractions of the biceps brachii muscle.

Abstract The aim of the present study was to examine the non-stationary mechanomyogram (MMG) during voluntary isometric ramp contractions of the biceps brachii muscles using the short-time Fourier transform, and to obtain more detailed information on the motor unit (MU) activation strategy underlying in the continuous MMG/force relationship. The subjects were asked to exert ramp contractions from 5% to 80% of the maximal voluntary contraction (MVC) at a constant rate of 10% MVC/s. The root mean squared (RMS) amplitude of the MMG began to increase slowly at low levels of force, then there was a slight reduction between 12% and 20% MVC. After that, a progressive increase was followed by a decrease beyond 60% MVC. As to the mean power frequency (MPF), a relatively rapid increase up to 30% MVC was followed by a period of slow increment between 30% and 50% MVC. Then temporary reduction at around 50% MVC and a further rapid increase above 60% MVC was observed. The interaction between amplitude and MPF of the MMG in relation to the MU activation strategy is discussed for five force regions defined on the basis of their inflection points in the RMS-amplitude/force and MPF/force relationships. It was found that the MMG during ramp contractions enables deeper insights into the MU activation strategy than those determined during traditional separate contractions. In addition, this contraction protocol is useful not only to ensure higher force resolution in the MMG/force relationship, but also to markedly shorten the time taken for data acquisition and to reduce the risk of fatigue.

Acoustic and electrical activities during voluntary isometric contraction of biceps brachii muscles in patients with spastic cerebral palsy

This study was designed to compare electromyogram (EMG) and acoustic myogram (AMG) recordings of biceps brachii muscles in patients with spastic cerebral palsy (CP). The maximal voluntary contraction (MVC) in the CP group was approximately one half of that of the normal group even after being normalized by the muscle cross‐sectional area (CSA) (18.6 ± 5.9 kNm/m2 in CP, 37.3 ± 2.9 kNm/m2 in normal). Both CP and normal groups demonstrated a progressive increase in the root mean squared values per unit muscle CSA in the EMG (RMSEMG/CSA) as well as in the AMG (RMSAMG/CSA) with increasing force up to 50% MVC. The increasing magnitude of the RMSEMG/CSA with force was not significantly different between two subject groups. However, all the levels of force resulted in significantly smaller RMSAMG/CSA in the CP group compared to the normal group. The ratios of RMSAMG to RMSEMG in the CP group (0.75 ± 0.03 m/s2/mV) were significantly smaller than those in the normal group (1.37 ± 0.07 m/s2/mV) at force levels above 30% MVC. These results suggest that motor disabilities in CP patients are caused not only by primary neural impairment but also by secondary deterioration in muscular contractile properties, probably resulting from muscle fiber atrophy. This appears to be more selective in fast twitch fibers.

Mechanomyographic responses during voluntary ramp contractions of the human first dorsal interosseous muscle

The aim of this study was to examine the mechanomyogram (MMG) and force relationship of the first dorsal interosseous (FDI) muscle as well as the biceps brachii (BB) muscle during voluntary isometric ramp contractions, and to elucidate the MMG responses resulting from the intrinsic motor unit (MU) activation strategy of FDI muscle with reference to the MMG of BB muscle. The subjects were asked to exert ramp contractions of FDI and BB muscle from 5% to 70% of the maximal voluntary contraction (MVC) at a constant rate of 10% MVC/s. In FDI muscle, the root-mean-squared amplitude (RMS) of the MMG decreased slowly with force up to 21%, and then a progressive increase was followed by a relatively rapid decrease beyond 41% MVC. The RMS/%MVC relationship in BB muscle consisted of an initial slow increase followed by a rapid increase from 23% MVC and a progressive decrease beyond 61% MVC. With respect to the mean power frequency (MPF), FDI muscle demonstrated no obvious inflection point in the MPF/%MVC relationship compared with that in BB muscle. Namely, the MPF of FDI muscle increased linearly through the force levels exerted. In contrast to FDI muscle, the MPF/%MVC relationship in BB muscle was decomposed into four specific regions: (1) a relative rapidly increase (<34% MVC), (2) a slow increment (34–53% MVC), (3) a temporary reduction (53–62% MVC), and (4) a further rapid increase (>62% MVC). The different MMG responses between FDI and BB muscles are considered to reflect the fact that the MU activation strategy varies among different muscles in relation to their morphology and histochemical type. Namely, the rate coding of the MUs plays a more prominent role in force production in relatively small FDI muscle than does MU recruitment compared with their respective roles in the relatively large BB muscle.

Age-related change in motor unit activation strategy in force production: a mechanomyographic investigation.

This study was designed to examine the effect of increasing age on the recruitment and activation of motor units (MU) in the biceps brachii muscle, using the mechanomyogram (MMG)/force relationship during isometric ramp contractions. The relationships between the root mean squared amplitude (RMS) and mean power frequency (MPF) of the MMG and relative force (% MVC) in the elderly (male, n = 10, age = 69.8 ± 4.7 years, mean ± SD) were markedly different from those in the young group (male, n = 15, age = 22.7 ± 1.8 years). In elderly individuals, the RMS increased progressively with force up to 57.6 ± 3.4% MVC, when a brief rapid increase was followed by a stable trend beyond 63.6 ± 3.7% MVC. The MPF increased slowly up to 59.4 ± 2.3% MVC; after a temporary reduction from 59.4% to 64.3 ± 2.0% MVC, it then increased progressively again. In conjunction with absolute force (Fabs), both the RMS and MPF in the elderly were smaller than those in the young group throughout the submaximal levels of force exerted. The results reflect an alteration in MU activation strategy, with a predominant role for MUs with slow‐twitch fibers and an effective fused tetanus induced at lower firing rate of the MUs, resulting from age‐related neuromuscular changes.

Age-related changes in the interactive mobility of the hip and knee joints: a geometrical analysis

This study examined any systematic age-related change in the passive range of motion (PROM) of the hip and knee joints. Seventy-seven healthy male volunteers ranging in age from 15 to 73 years were assessed. A geometrical range of motion (ROM) analysis was applied, which could evaluate the effects of both monoarticular and biarticular muscles. The PROM of the hip joint decreased progressively with advancing age, whereas that of the knee joint remained unchanged. In addition, the interactive PROM of the hip and knee joint associated with biarticular rectus femoris and hamstring muscles also showed an age-related reduction. The progressive reduction of the ROM is probably caused by shortening of muscles or connective tissues due to reduced compliance of joint structures and degenerative changes in spinal alignment, as well as by diminished muscle stretching resulting from a decrease in daily physical activities with advancing age.

Relationship between mechanomyogram and force during voluntary contractions reinvestigated using spectral decomposition

Abstract A mechanomyogram (MMG) is considered to represent the pressure waves resulting from the lateral expansion of contracting muscle fibers. However, the actual MMG recording appears not only to reflect lateral changes of active fibers, but also to include the effect of their longitudinal shortening, because the fiber orientation, particularly in pennate muscles, is not parallel with the MMG transducer attached at the skin surface. In the present investigation, a spectral decomposition method was developed to eliminate the interference due to fiber longitudinal movement from the MMG recording. The MMG was recorded over the belly of the rectus femoris muscle, which is a pennate muscle. Vibration over the tibial tuberosity (VTT) was used as a measure of the integrated longitudinal movement of the muscle fibers. The lateral and longitudinal components included in the MMG were separated by a spectral decomposition method that is based on the coherence function of the MMG and VTT. The MMG/force relationship was compared between the original and decomposed MMG. One-third of the 12 subjects demonstrated a curvilinear relationship between the original MMG and force throughout the range of force. In the other two-thirds, the MMG saturated or reduced beyond 70% of the maximum voluntary contraction (MVC). After decomposition, the MMG increased progressively with force up to 70% MVC, beyond which it decreased in all subjects. The spectral decomposition method described here is considered to be a useful tool with which to examine in more detail the MMG/force relationship of different pennate muscles.

Survival Prognosis of Japanese With Severe Motor and Intellectual Disabilities Living in Public and Private Institutions Between 1961 and 2003

Background Although the prognosis for survival in people with severe functional disabilities is a serious concern for their families and health care practitioners, there have been few reports on survival rates for this population. Every year, the Japanese Association of Welfare for Persons with Severe Motor and Intellectual Disability collects anonymous records of individual registrations and deaths from all private and public institutions, excepting national institutions. We used these data to estimate the prognosis for survival. Methods We reviewed the records of 3221 people with severe motor and intellectual disabilities (SMID); all subjects had lived in one of 119 public or private institutions in Japan between 1961 and 2003. Kaplan–Meier survival estimates were calculated according to disability type and birth year range. Results Of the 3221 persons, 2645 were alive and 576 had died. The survival rate at the age of 20 for all subjects was 79% (95% confidence interval, 78%–81%). Among people who were unable to sit, those with lower intelligence quotients had lower survival rates. Conclusions The survival rate among people with SMID housed in public and private institutions in Japan was much worse than that of the general population, and has not improved since the 1960s.

Geometrical analysis of hip and knee joint mobility in cerebral palsied children

The present investigation attempted to define a geometrical hexagon model for representing the sagittal range of motion (ROM) of hip and knee joint. The effect of both monoarticular and biarticular muscles on joint mobility in children with spastic cerebral palsy (SCP) were analyzed by this geometrical method. Photographic analysis was used to measure hip and knee joint angle at six different boundary positions. The ROM in normal children indicated age dependent reduction of maximal hip flexion and shortening of hamstring and rectus femoris muscles. A number of SCP children showed greater reduction of both hip flexion and extension and shortening of hamstring and rectus femoris muscles, whereas the ROM of knee joint was similar to that in normal children. The deteriorated hip joint mobility seems to be associated with shortening of muscle due to their intrinsic spasticity. The impaired ROM was more noticeable in SCP non-ambulator child than in independent ambulator. Thus, more extended range and frequent opportunity of joint motion may play an important role in improving the joint mobility in this patient group. Copyright 1998 Elsevier Science B.V.

Frequency response model of skeletal muscle and its association with contractile properties of skeletal muscle

The aims of the present study were to develop a mathematical model of the skeletal muscle based on the frequency transfer function, referred to as frequency response model, and to presume the relationship between the model elements and skeletal muscle contractile properties. Twitch force in elbow flexion was elicited by applying a single electrical stimulation to the motor point of biceps brachii muscles, and then analyzed visually by the Bode gain and phase diagram of the force signal. The frequency response model was represented by a frequency transfer function consisting of five basic control elements (proportional element, dead time element, and three first-order lag elements). The model element constants were estimated by best-fitting to the Bode gain and phase diagram of the twitch force signal. The proportional constant and the dead time in the frequency response model correlated significantly with the peak torque and the latency in the actual twitch force, respectively. In addition, the time constants of the three first-order lag elements in the model correlated strongly with the contraction time and the half relaxation time in the actual twitch force. The results suggested a possibility that the individual elements in the frequency response model would reflect the biochemical and biomechanical properties in the excitation-contraction coupling process of skeletal muscle.

Hemodynamic and hormonal changes during lower body negative pressure in bedridden disabled patients

Hemodynamic responses and hormonal changes induced by lower body negative pressure (LBNP) were measured in bedridden patients with severe disabilities to identify their cardiovascular function. After a control period of 5 minutes supine, each subject underwent a LBNP test of ‐20 mmHg for 5 minutes. Disabled patients were classified into two groups: Group HI consisted of the members who had a blood pressure response to LBNP exposure similar to normal control subjects, and group H2 patients displayed a greater reduction in blood pressure than the normal response. Both disabled groups demonstrated a significantly higher level of resting heart rate as well as a smaller stroke volume and cardiac output than normal subjects. Exposure to LBNP in disabled patients produced a smaller decrement in stroke volume and cardiac output than in normal subjects. The expected increase in heart rate for the compensatory effect was not observed in the HI group, and a decreased heart rate lower than resting values was measured...