Akira Iwata

Characteristics of locomotion, muscle strength, and muscle tissue in regenerating rat skeletal muscles

Although numerous studies have aimed to elucidate the mechanisms used to repair the structure and function of injured skeletal muscles, it remains unclear how and when movement recovers following damage. We performed a temporal analysis to characterize the changes in movement, muscle function, and muscle structure after muscle injury induced by the drop‐mass technique. At each time‐point, movement recovery was determined by ankle kinematic analysis of locomotion, and functional recovery was represented by isometric force. As a histological analysis, the cross‐sectional area of myotubes was measured to examine structural regeneration. The dorsiflexion angle of the ankle, as assessed by kinematic analysis of locomotion, increased after injury and then returned to control levels by day 14 post‐injury. The isometric force returned to normal levels by day 21 post‐injury. However, the size of the myotubes did not reach normal levels, even at day 21 post‐injury. These results indicate that recovery of locomotion occurs prior to recovery of isometric force and that functional recovery occurs earlier than structural regeneration. Thus, it is suggested that recovery of the movement and function of injured skeletal muscles might be insufficient as markers for estimating the degree of neuromuscular system reconstitution. Muscle Nerve 41: 694–701, 2010

Cyclic modulation of H-reflex depression in ipsilateral and contralateral soleus muscles during rhythmic arm swing

The objective of the present study was to investigate the effects of rhythmic arm swing on ipsilateral and contralateral soleus motoneuron pool excitability. Ten healthy human subjects participated in this study. Soleus H-reflexes were recorded from the ipsilateral and contralateral soleus muscles while the subject swung the right arm anteroposteriorly as if during gait. The soleus H-reflex was depressed throughout the whole arm swing cycle except in the ipsilateral leg during the onset of the backward arm swing, and in the contralateral leg during the last half of the backward arm swing and the onset of the forward arm swing. The depression was cyclically modulated in accordance with the time course of the arm swing periods, and the pattern of the modulation was reciprocal between the ipsilateral and contralateral legs. This cyclical and reciprocal modulation may be related to the regulation of soleus motoneuron pool excitability during gait.

Improvement of Endurance Based on Muscle Fiber-Type Composition by Treatment with Dietary Apple Polyphenols in Rats

A recent study demonstrated a positive effect of apple polyphenol (APP) intake on muscle endurance of young-adult animals. While an enhancement of lipid metabolism may be responsible, in part, for the improvement, the contributing mechanisms still need clarification. Here we show that an 8-week intake of 5% (w/w) APP in the diet, up-regulates two features related to fiber type: the ratio of myosin heavy chain (MyHC) type IIx/IIb and myoglobin protein expression in plantaris muscle of 9-week-old male Fischer F344 rats compared to pair-fed controls (P < 0.05). Results were demonstrated by our SDS-PAGE system specialized for MyHC isoform separation and western blotting of whole muscles. Animal-growth profiles (food intake, body-weight gain, and internal-organ weights) did not differ between the control and 5% APP-fed animals (n = 9/group). Findings may account for the increase in fatigue resistance of lower hind limb muscles, as evidenced by a slower decline in the maximum isometric planter-flexion torque generated by a 100-s train of electrical stimulation of the tibial nerve. Additionally, the fatigue resistance was lower after 8 weeks of a 0.5% APP diet than after 5% APP, supporting an APP-dose dependency of the shift in fiber-type composition. Therefore, the present study highlights a promising contribution of dietary APP intake to increasing endurance based on fiber-type composition in rat muscle. Results may help in developing a novel strategy for application in animal sciences, and human sports and age-related health sciences.

Knee adduction moment and medial knee contact force during gait in older people

External knee adduction moment has been studied as a surrogate for medial knee contact force. However, it is not known whether adduction moment is a rational measure for predicting medial knee contact force. The aim of this study was to investigate the correlation between knee adduction moment and medial knee contact force in older people, using musculo-skeletal simulation analysis. One hundred and twenty-two healthy older subjects participated in this study. Knee moment and medial knee contact force were calculated based on inverse dynamics analysis of normal walking. Muscle force and joint reaction force were used to determine the medial knee contact force during stance phase. The results showed that the maximum medial knee contact force was moderately correlated to the maximum knee adduction (r = 0.59) as well as the maximum extension moment (r = 0.60). The first peak of medial knee contact force had a significant strong correlation with the first peak of adduction moment and a moderate correlation with the maximum flexion moment. The second peak of medial knee contact force had a significant moderate correlation with both the second peak of adduction and the maximum extension moment. These results implied that the maximum adduction moment value could be used, to some extent, as a measure of the maximum medial knee contact force.

PREMOVEMENT FACILITATION OF CORTICOSPINAL EXCITABILITY BEFORE SIMPLE AND SEQUENTIAL MOVEMENT

The purpose of this study was to investigate whether premovement facilitation of corticospinal excitability before sequential movement was different from that before simple movement. Each of 7 participants who performed choice reaction tasks with the right hand pressed a force transducer with the index finger in response to a start cue or pressed the transducers sequentially with the index finger, little finger, thumb, little finger, and index finger. Transcranial magnetic stimulation was delivered to the left motor cortex before the electromyographic burst in the first dorsal interosseous muscle and motor evoked potentials were recorded from the first dorsal interosseous muscle. The amplitude of the motor-evoked potential increased as its onset got closer to the onset of the electromyographic burst. The increase before the sequential movement was larger and began earlier than that before the simple movement. These findings indicate that premovement facilitation of corticospinal excitability is different in magnitude and timing between sequential and simple movements.

Quickness of trunk movements in a seated position, regardless of the direction, is more important to determine the mobility in the elderly than the range of the trunk movement

Although trunk function is known to be critical for maintaining balance during gait, a detailed evaluation regarding the relationship between trunk function and mobility has not been performed. We previously reported that the ability of quick lateral trunk movements in a seated position reflects mobility in elderly people. In this study, we further examined whether trunk movement in the anterior-posterior direction is also a determinant of mobility. In addition, the correlation between range of lateral trunk movement and mobility was also examined. One hundred and forty community-dwelling elderly participants (73.3±6.2 years) were enrolled in this study. We performed various trunk movement tests in a seated position, such as the seated side tapping test (SST), the seated anterior-posterior tapping test (APT), and the lateral sitting functional reach test (sitting reach test). Maximum gait speed and the timed up and go test (TUG) were performed to determine mobility. Parameters of trunk movement were compared. SST and APT showed moderate significant correlations with both maximum gate speed and TUG, while the sitting reach test weakly correlated (SST r=-0.58, p<0.01, APT r=-0.63, p<0.01, sitting reach test r=0.30, p<0.01). Moreover, multiple regression analysis revealed that SST and APT were independent indicators of both maximum gate speed and TUG, while the sitting reach test was not. These findings indicate that quickness, regardless of the direction of the movement, is more important than range in determining mobility in the elderly.

Premovement facilitation of corticospinal excitability in patients with Parkinson's disease.

ABSTRACT The purpose of this study was to investigate the abnormality of premovement facilitation in patients with Parkinsons disease. Seven patients with Parkinsons disease and seven healthy subjects participated in this study. The subjects attempted abduction of the index finger in response to a visual start cue, and motor-evoked potentials were recorded from the first dorsal interosseous muscle before movement onset. The rate of premovement facilitation in patients with Parkinsons disease was slower than that in healthy subjects. Additionally, the rate of premovement facilitation as a function of delay from the start cue was positively correlated with the reaction time. These findings indicate that premovement facilitation is abnormal in patients with Parkinsons disease. This abnormality may be partially related to akinesia.

Sit-to-stand movement changes in preschool-aged children with spastic diplegia following one neurodevelopmental treatment session – a pilot study

Abstract Purpose: This study was designed to provide a better understanding of how a single neurodevelopmental treatment (NDT) session affects sit-to-stand (STS) movements in children with cerebral palsy (CP). Methods: Eight children with spastic diplegia and five typically developing children, aged 4–6 years, participated in this study. The CP participants performed STS movements immediately before and after a 40-min NDT session. Using a three-dimensional, four-camera analysis system, angular movements involving the hip, knee and ankle joints of the participants were obtained. Results: During forward tilt of the trunk, the maximum and final angles after the NDT session significantly decreased compared with those before the session (p < 0.05, p < 0.01). Moreover, the final hip flexion after the session also significantly decreased compared with that before the session (p < 0.01). On the other hand, the initial, maximum and final ankle dorsiflexion angles after the session were significantly greater (p < 0.05, p < 0.01 and p < 0.05, respectively) than before the session. Conclusions: These findings suggest that a single NDT session enables children with CP to stand from a seated position without using some atypical movement patterns. Implications for Rehabilitation Preschool-aged children with spastic diplegia, with limited ability to independently transfer from a sitting position, and dependent on a wheelchair for mobility experience obstacles to enhanced activities of daily life and social participation. A single neurodevelopmental treatment session would enable children with spastic diplegia to perform sit-to-stand movements more efficiently, with selective muscle control. Understanding how a single neurodevelopmental treatment session affects sit-to-stand movements in children with spastic diplegia is invaluable for therapists planning more efficient therapeutic programs and may enable children with spastic diplegia to develop improved mobility

Maximum movement velocity of the upper limbs reflects maximum gait speed in community-dwelling adults aged older than 60 years.

A number of studies have shown that the maximum movement velocity of the lower limbs is a critical determinant of gait speed in elderly adults. However, it is still unclear whether gait speed is associated with the movement velocity of the lower limbs or the movement velocity itself. Therefore, we measured the movement velocity of upper limbs that would not have a direct effect on gait, and examined the relationship between the movement velocity and gait speed.

The association between intersegmental coordination in the lower limb and gait speed in elderly females

Human multi-segmental motion is a complex task requiring motor coordination. Uncoordinated motor control may contribute to the decline in mobility; however, it is unknown whether the age-related decline in intersegmental coordination relates to the decline in gait performance. The aim of this study was to clarify the association between intersegmental coordination and gait speed in elderly females. Gait measurements were performed in 91 community-dwelling elderly females over 60 years old. Foot, shank, and thigh sagittal motions were assessed. Intersegmental coordination was analyzed using the mean value of the continuous relative phase (mCRP) during four phases of the gait cycle to investigate phase differences in foot-shank and shank-thigh motions during a normal gait. The results showed that foot-shank mCRP at late stance had negative correlations with gait speed (r=-0.53) and cadence (r=-0.54) and a positive correlation with age (r=0.25). In contrast, shank-thigh mCRP at late stance had positive correlations with gait speed (r=0.37) and cadence (r=0.56). Moreover, partial correlation, controlling age, height, and weight, revealed that foot-shank mCRP at late stance had negative correlations with gait speed (r=-0.52) and cadence (r=-0.54). Shank-thigh mCRP at late stance had a positive correlation with gait speed (r=0.28) and cadence (r=0.51). These findings imply that the foot-shank and shank-thigh coordination patterns at late stance relate to gait speed, and uncoordinated lower limb motion is believed to be associated with the age-related decline in cadence.