Kyonosuke Yabe

Bone mineral density differences between paraplegic and quadriplegic patients: a cross-sectional study.

Study design: This cross-sectional study was conducted by comparing bone mineral density (BMD) of paraplegic and quadriplegic patients.Objectives: The purpose of this study was to investigate the relationship between the bone mineral loss and injury level in spinal cord injury patients.Settings: Experiments were conducted at Yoneda Hospital and Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan.Methods: Lumbar spine (L2-4), proximal femur (femoral neck, trochanter region and Wards triangle) and whole body BMD were measured in ten paraplegic and ten quadriplegic patients using dual-energy X-ray absorptiometry (DXA, HITACHI BMD-1X).Results: Significant differences were observed in the lumbar spine, trochanter region and upper extremities BMD between paraplegic and quadriplegic patients (P<0.05, P<0.05 and P<0.01, respectively), but not in the femoral neck, Wards triangle, head, pelvis, lower extremities or whole body BMD.Conclusion: These results suggest that the injury level influences on the lumbar spine, upper extremities and trochanter region BMD. From a biomechanical standpoint, it is possible to explain that the differences in mechanical loading exerted on bones also affected the difference of lumbar spine BMD in the two groups.

Age comparison of H-reflex modulation with the Jendrássik maneuver and postural complexity

OBJECTIVE The purpose of this study was to examine modulation of the soleus Hoffmann (H)-reflex in response to the Jendrássik maneuver (JM) in standing positions in young and elderly subjects. METHODS Seventeen elderly (mean age=72.0 years) and 23 young (mean age=23.2 years) apparently healthy subjects were examined in two separate experiments. The first experiment was conducted to compare the prone and standing position. The second experiment was conducted in the standing position with isotonic glideboard back support. The isotonic glideboard back support was inclined 30 degrees. In the standing position with back support, the knee and ankle joints were set at 0 degrees of flexion. All subjects were tested with two foot-positions: (1) with no soleus contraction on the platform (simple task) and (2) with an active calf muscle group contraction (complex task). To compare the amplitude of the H-reflex in each experiment between the control trials (relaxed) and JM trials (squeezing tennis balls), the stimulus intensity of 1.1 x motor threshold of the M-response was used for each subject in all body positions. RESULTS To ensure experimental control, subjects did not show a difference in the amplitude of the trial M-response between the control and JM trials on any of the body positions. Also, no difference was found in the mean amplitude of the M-response between two different positions in either of the two experiments. Trial M-responses were all between 13 and 17% of M-max in the quiet standing position for the young subjects, and 17 and 21% for the elderly subjects. Results demonstrated that the JM facilitated the H-reflex in both young and elderly subjects. However, differential ability to modulate motoneuron excitability evoked by H-reflex pathways was found between the two groups. Young subjects demonstrated a significant difference in the amplitude of the H-reflex between control and JM trials in each standing position (P<0.05). The elderly subjects, in contrast, demonstrated no significant difference in the amplitude of the H-reflex between control and JM trials during normal standing. When examining standing with back support, the young subjects demonstrated a significant difference in the amplitude of the H-reflex between control and JM trials during both the simple and complex tasks (P<0.05). The elderly subjects, in contrast, demonstrated a significant difference only in the simple postural task (P<0.05). CONCLUSIONS These results provide evidence of differential human spinal reflex modulation between young and elderly subjects. Further, these results may point towards the role of presynaptic inhibition in mediating these differences, and may lead to a more complete understanding of the different postural control strategies between young and elderly subjects.

Effects of high-intensity resistance training on bone mineral density in young male powerlifters

Abstract. The effects of high-intensity resistance training on bone mineral density (BMD) and its relationship to strength were investigated. Lumbar spine (L2-L4), proximal femur, and whole body BMD were measured in 10 male powerlifters and 11 controls using dual-energy X-ray absorptiometry (DXA). There were significant differences in lumbar spine and whole body BMD between powerlifters and controls, but not in proximal femur BMD. A significant correlation was found between lumbar spine BMD and powerlifting performance. These results suggest that high-intensity resistance training is effective in increasing the lumbar spine and whole body BMD.

Relationships of muscle strength and power with leisure‐time physical activity and adolescent exercise in middle‐aged and elderly Japanese women

Aim:  The purpose of the present study is to assess the relationships of muscle strength and power with recent leisure‐time physical activity and exercise during adolescence in middle‐aged and elderly Japanese women.

Effects of pre-motion electromyographic silent period on dynamic force exertion during a rapid ballistic movement in man.

SummaryThe effects of pre-motion silent period (PSP) on dynamic force exertion were studied in ten healthy subjects performing ballistic elbow extensions. The experiments were designed to evaluate the significance of mean differences between the averaged dynamic force curves of two groups: PSP-presence groups and PSP-absence groups. The presence of PSP was judged quantitatively and automatically by means of a newly developed method using statistical analysis. The results indicated that there were two effects of PSP on dynamic force exertion: one was a reducing effect, observed prior to the movement; the other was a reinforcing effect, observed in the first part of the ballistic movement. The duration of the reinforcement was significantly correlated with the duration of the reducing effect of PSP. The findings suggested that the reinforcement of dynamic force may be produced by the pre-stretch of agonistic muscles caused by prior force reduction due to PSP occurrence. The fact that PSP plays an important role in dynamic force exertion suggests that PSP may be incorporated in the central motor control system designed to interrupt the background activity, to stretch the agonist and to reinforce the dynamic force.

In vivo behaviour of human muscle architecture and mechanomyographic response using the interpolated twitch technique

This study investigated the origin of curvilinear change in the superimposed mechanomyogram (MMG) amplitude of the human medial gastrocnemius muscle (MG) with increasing contraction intensity. The superimposed twitch amplitude, the superimposed MMG amplitude and the extent of fascicle shortening were measured using ultrasonic images of electrical stimulation during isometric plantar flexions at levels 20%, 40%, 60%, 80%, and 100% of the maximal voluntary contraction (MVC). The superimposed twitch amplitude, the superimposed MMG amplitude and the extent of fascicle shortening decreased with increasing contraction intensity. The superimposed MMG amplitude and the extent of fascicle shortening showed a curvilinear decrease, while the superimposed twitch amplitude showed a linear decrease at levels up to 80% of the MVC. There was a linear relationship between the superimposed MMG amplitude and the extent of fascicle shortening at different contraction intensities. These results indicate that the superimposed MMG amplitude reflects changes in the extent of fascicle shortening at different contraction intensities better than the superimposed twitch amplitude. Our study suggests that the origin of the curvilinear decrease of superimposed MMG amplitude is associated with a curvilinear decrease of the extent of fascicle shortening with increasing contraction intensity in the human MG.

Changes in force and tendinous tissue elongation during the early phase of tetanic summation in in vivo human tibialis anterior muscle

The purpose of this study was to determine the changes that occur in tendinous tissue properties during the early phase of tetanic summation in the in vivo human tibialis anterior muscle (TA). The torque response and tendinous tissue elongation following single stimuli, two-pulse trains, and three-pulse trains were recorded in the TA during isometric contractions. The elongation, compliance, and lengthening velocity of tendinous tissue were determined by real-time ultrasonography. The contribution of the response to the second stimulation (C2) was obtained by subtracting the response to the single stimulation (C1) from the response of doublet. The third contribution (C3) was obtained by subtracting the response to the doublet from that of the triplet. C2 (7.8+/-0.5 Nm) and C3 (7.3+/-0.6 Nm) had torque responses significantly higher than C1 (3.6+/-0.7 Nm). In contrast, the elongations of tendinous tissue for C2 (2.8+/-0.4mm) and C3 (1.7+/-0.2mm) were significantly lower than for C1 (4.9+/-0.3mm), indicating that the summation pattern of tendinous tissue elongation is different from the summation pattern of torque response. In addition, this showed considerable difference both between C1 (0.12+/-0.01 mm/N; 83+/-4.6mm/s) and C2 (0.03+/-0.005 mm/N; 50+/-6.3mm/s) and between C1 and C3 (0.02+/-0.002 mm/N; 39+/-6.4mm/s) in the compliance and lengthening velocity of tendinous tissue. These results suggest that changes in tendinous tissue properties between first and second contraction are related to different summation patterns of force and tendinous tissue elongation during early phase of tetanic summation.

Effects of premotion silent period on single motor unit firing at initiation of rapid contraction

We compared the single motor unit (SMU) activity between movements with a premotion silent period (PMSP) and without PMSP in EMG. Fourteen SMUs in the gastrocnemius muscle and 6 SMUs in the soleus muscle were recorded from 5 volunteers during isometric plantar flexion. Tonically firing SMUs failed to fire just before the onset of a rapid contraction with PMSP more frequently than without PMSP. SMUs tended to fire within 10 msec (the gastrocnemius SMUs) or 20 msec (the soleus SMUs) from the onset of the phasic EMG discharge when PMSP occurred. In a rapid contraction without PMSP, the initial firing of SMUs occurred with longer latency than that in a rapid contraction with PMSP. The latency of the initial SMU firing in a rapid contraction related to the preceding time of the last SMU firing during a sustained contraction to the onset of the phasic EMG discharge. When the preceding firing was long enough, the latency distributed around 10 msec. On the other hand, for shorter preceding times, the latency lengthened with shortening of the preceding time. It is suggested that the PMSP makes the preceding time long and increases the susceptibility of motor units to the descending command at the initiation of a rapid contraction.

Adapted Physical Activity

Adapted physical activity pedagogy is dynamic, exciting, and challenging. Beliefs, attitudes, and actions toward people with special needs have changed enormously, demanding new ways of thinking and doing. This paper summarizes current thought about (a) philosophy, theory, and practices; (b) negative attitudes and perceived lack of competence of teachers as the greatest barriers to service; (c) principles to guide public school consultant services; (d) a new definition of adapted physical activity; and (e) emerging pedagogical theory that emphasizes integration of knowledge about individual differences, adaptation, and creativity. Adapted physical education specialists should be employed in every community to work directly with students who are disabled and to act as consultants and administrators to help regular educators change· attitudes and practices. Assessment, the foundation of pedagogy, should address both individual differences and environmental barriers. Behavior change should be promoted through application of adaptation and creativity theory. Adaptation theory, first posited by Ernst Kiphard of Germany, stresses working with both the individual and the environment in a continuous, dynamic, and bidirectional manner to achieve educational goals. Creativity theory, advanced by Sherrill, stresses fluency, flexibility, originality, and elaboration as key elements of adapted physical activity pedagogy.

The effect of summation of contraction on acceleration signals in human skeletal muscle.

The purpose of this study was to determine the effects of summation of contraction on acceleration signals in human skeletal muscle. The torque parameters of dorsiflexion and acceleration signals in the tibialis anterior muscle were measured during evoked isometric contractions. In an examination of two-pulse trains with different inter-pulse intervals, the torque and accelerometer responses to inter-pulse intervals of 10-100 ms were recorded. In an investigation of the effects of different numbers of stimuli, the torque and accelerometer responses to 1-8 pulses with a constant inter-pulse interval of 10 ms were recorded. The present study found that there was a difference in acceleration amplitude between the single-pulse and two-pulse trains with an inter-pulse interval of 10 ms but not two-pulse trains with an inter-pulse interval of 20 ms or more. In the investigation of different numbers of stimuli, we found a similar MMG amplitude across 2-8 pulses. Moreover, we observed that the maximal time to the peak acceleration signal was approximately 27 ms. In a comparison of torque parameters with acceleration signals, the present study clearly shows that acceleration amplitude is poorly correlated to changes in force parameters when the inter-pulse interval or the number of stimuli are increased. These results suggest that the absence of associated changes in acceleration peak is due to the long interval for the subsequent pulses relative to the time at which acceleration peak is achieved ( approximately 27 ms). These findings will provide useful information concerning the method for assessing summation of contraction with an accelerometer.