Makoto Watakabe

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.

The effects of mechanical compression and hypoxia on nerve root and dorsal root ganglia. An analysis of ectopic firing using an in vitro model.

Study Design This study analyzed in vitro experiments of ectopic firing evoked by mechanical compression or hypoxia of canine lumbar dorsal roots with dorsal root ganglia using an in vitro model. Objectives The results were correlated to understand the pathophysiology of radiculopathy, which manifests abnormal sensation and pain. Summary of Background Data It has been speculated that blood flow in the nerve root and mechanical compression play major roles in the production of radiculopathy symptoms. However, no precise experimental studies have been conducted on the relationship between these factors and the development of ectopic firing. Methods Canine lumbar dorsal roots with dorsal root ganglia were immersed in an oxygenated artificial cerebrospinal fluid, and activity of the nerve root was recorded using bipolar platinum electrodes. Using this model, the effects of quantitative mechanical compression and hypoxia on the ectopic firing were analyzed. Results When compression was applied, mechanical thresholds for eliciting firing were much lower in dorsal root ganglia than in dorsal roots, and the firing lasted for a longer period in dorsal root ganglia. Under hypoxia, dorsal root ganglia showed firing, and their thresholds from mechanical stimuli decreased significantly. In dorsal roots, impulse propagation was not affected, whereas firing was seen under the hypoxic condition. Conclusion Dorsal root ganglia are highly sensitive to mechanical compression and hypoxia and closely related to abnormal sensations and pain in radiculopathy.

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.

Analysis of spinal cord evoked potential and locomotor function during acute spinal cord compression in cats

The aim of this study was to investigate whether or not conductrive spinal cord evoked potentials and spinal cord function change correspondingly with each other. The relationship between conductive spinal cord evoked potentials and locomotor function during acute spinel cord compression in animals was investigated. In decerebrate cats, controlled locomotion can be induced by electrical stimuli in the mesencephalic locomotor region. Conductive spinal cord evoked potentials were recorded at the L3 level of the spinal cord and stimuli were given at the T4 cogment. The locomotor function was evaluated through electromyograms of the hind limbs. By compressing the spinal cord at L1, both the conductive spinal cord evoked potentisls and the locomotor function gradually decreased. When the first negative potential amplitude of conductive spinal cord evoked potentials was decreased to half the level found in normals cats, locomotor function was injured irreversibly. These results showed that changes in teh conductive spinal cord evoked potentials were related to changes in locomotor function. The 50% level of the first negative potential amplitude was considered to be the critical level at which irreversible spinal cord paralysis occurred in the cats.

Change in heart rate variability in bedridden patients with severe physical disability

The change in power spectral density of heart rate variability (HRV) during sitting and to an exposure to lower body negative pressure of ‐20 mmHg was estimated in 21 bedridden patients with severe...

A Simulation Study on Walking Disabilities Associated with Restriction of Joint Range of Motion.

The restriction of the range of motion (ROM) of joints is one of the major causes contributing to walking disabilities as well as neural dysfunction and decreased muscle force. This study was designed to develop a biomechanical model of walking consisting of both the neural and muscunloskeletal systems, and to simulate the characteristics of walking disability due to restriction of the ROM of hip and knee joints. The neural and muscunloskeletal functions in the present model were represented by neural oscillators and a two-dimensional five-link model, respectively. The walking patterns produced under the non restricted ROM of the joints were similar to those obtained from normal individuals. The simulation with the restricted ROM of joints demonstrated more unstable walking with increasing severity of the joint impairments as well as with increasing walking velocity. Even if the ROM of hip and/or knee joints of this model was restricted, both stride length and cadence during stable walking were within the range determined from normal individuals. However, the vertical acceleration of the body center of gravity was considerably greater during walking with the restricted joints compared with free joint movement. These characteristics obtained from the simulation were very similar to those of disabled walking produced experimentally by healthy subjects whose lower limb joints were restricted by orthotic devices. It is considered that the present biomechanical model/simulation is a useful way to identify a single cause such as joint contracture from the multiple and complex impairments associated with walking disabilities and to assess the degree of the disabilities due to the specified impairment.

Biomechanical Analysis of Alignment in Standing Posture in Children with Cerebral Palsy.

The purpose of this study is to determine the quantitative relationship between the restriction of the ROM (range of motion) of joints and alignment in standing posture in children with cerebral palsy (CP). The measurement of alignment was carried out on three planes : horizontal, backward-inclined and forward-inclined planes. Alignment in CP children without a restricted ankle joint (NR-CP) was similar to that in normal subjects who can maintain an upright posture on any plane merely by adjusting the ankle joint alone. CP children with a restricted ankle joint (R-CP) demonstrated a severe crouching posture characterized by a forwardly inclined trunk, backwardly inclined thigh and forwardly inclined leg. This pathological posture may result not only from the contracture of the ankle joint but also from muscle shortening over the two joints. A biomechanical model of the restriction of the ROM was developed and used to simulate the alignment in a standing posture. The simulation results for normal and NR-CP subjects were consistent with the experimental measure. ments. However there was some difference between the simulation and the measurements for R-CP children, particularly for the forward-inclined plane. If the mathematical model used in this study accurately reflects the effect of the restriction of the ROM on the alignment, other factors such as impaired neuromuscular function might contribute to the difference. The present biomechanical approach is useful to develop effective measures for improving posture in CP children.