Tsugutake Yoneda

Changes in hardness of the human elbow flexor muscles after eccentric exercise

Abstract The purpose of this study was to investigate changes in muscle hardness after eccentric exercise of the elbow flexors muscles that produce muscle shortening and swelling. To assess muscle hardness, a pressure method was used in which the force required to deform the tissue (skin, subcutaneous tissue, muscle) was recorded. Eleven healthy male students performed 24 maximal eccentric actions of the elbow flexor muscles with their non-dominant arms. Muscle hardness, maximal isometric force (MIF), muscle soreness, plasma creatine kinase (CK) activity, relaxed elbow joint angle (RANG), upper-arm circumference (CIR) and B-mode ultrasound transverse images were measured before, immediately after, and 1–5 days after exercise. A long-lasting decrease in MIF, muscle swelling shown by increases in CIR and muscle thickness, large increases in plasma CK activity, and development of muscle soreness indicated that damage occurred to the elbow flexor muscles. The RANG had decreased by approximately 20° at 1–3 days after exercise and showed a gradual recovery thereafter. The CIR increased gradually after exercise and peaked on day 5 post-exercise, the mean amount of increase in CIR being 18 mm. Muscle hardness measured at the relaxed elbow position did not change until 3 days after exercise, but increased significantly (P < 0.01) on days 4 and 5 post-exercise. On the other hand, muscle hardness measured when forcibly extending the shortened elbow joint increased significantly (P < 0.01) with time and peaked at 3 days after exercise. Muscle hardness assessed by the pressure method seems to reflect changes in muscle stiffness and swelling.

Amplitude reduction of H-reflex during mental movement simulation in elite athletes

In order to investigate the changes of motoneuron excitability during mental simulation of a voluntary movement (motor imagery; MI), the soleus H-reflex and several activities of autonomic effectors were recorded simultaneously when MI of speed skate sprint was performed. The subjects were seven elite speed skate athletes ranging in age from 18 to 24 years old. They were all skilled in MI, and could imagine full vivid skating movement internally as if they were really exercising. The subjects were awake, relaxed and blindfolded. At first, rest (5 min), positive relaxation (4 min) and concentration periods (2.5 min) were set up. Then, after the previous announcement for the start, MI was initiated by the sound of a signal gun which was recorded by a tape recorder. MIs were continued for each subject from about 36 s to 38 s, and these imaging times were very close to the actual personal best records of each subject. The autonomic effectors represented by skin conductance response (SCR), heart rate (HR), and respiration rate (RSR) became remarkably active during MI in all trials. SCR was increased by 51% on the average. Furthermore, HR and RSR were increased by 57% and 76% respectively, compared with those during resting period. These changes in the autonomic effectors were all significant and were those which were activated in actual movements. The amplitudes of H-reflex were almost all constant before MI initiation. However, the reduction of the H-reflex amplitude arose just after the start and lasted to the end of MI.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensory processing during kinesthetic aftereffect following illusory hand movement elicited by tendon vibration

We investigated how the human sensory-motor system elicits a somatosensory aftereffect. Tendon vibration of a limb excites the muscle spindle afferents that contribute to eliciting illusory movements of the limb. After the cessation of vibration, a transient sensation in which the vibrated limb returns towards its original position (kinesthetic aftereffect) is often experienced, even in the absence of the afferent inputs recruited by the vibration. We vibrated the tendon of either the right wrist extensor or flexor muscle that elicited an illusory flexion or extension movement, which was followed by its corresponding extension or flexion aftereffect. First, we psychophysically investigated how the preceding illusory movement affects the aftereffect. Second, we examined the cortico-spinal excitability during the aftereffect to evaluate its changes from the time during the illusion. We measured the amplitude of the motor-evoked potential that is evoked by a single-pulse transcranial magnetic stimulation to the hand section of the contralateral motor cortex (M1). All 19 subjects experienced the aftereffect, and the amount of aftereffect was approximately 70% of the preceding illusion. During the illusion, the cortico-spinal excitability increased more in non-vibrated than in vibrated muscle, so as to reflect the illusory directions. During the aftereffect, the excitability was significantly reduced only in the non-vibrated muscle, with no change in the vibrated muscle, which, in turn, caused an opposite pattern in the unbalanced excitability between the two muscles, and the degree of unbalanced excitability was correlated with the sensation of aftereffect. The kinesthetic aftereffect seems to be elicited by a sensory process that is determined by the preceding illusory movements. Motor-cortical processing of the unbalanced sensory information from the stimulated and non-stimulated muscles may contribute to the elicitation of kinesthetic aftereffect.

Recruitment threshold force and its changing type of motor units during voluntary contraction at various speeds in man

The motor unit discharges in human hand muscles were recorded during voluntary isometric contraction. Bipolar wire electrodes were inserted in the right adductor pollicis muscle (AP) and first dorsal interosseous muscle (FDI) for the recordings. Motor unit activities from these muscles were investigated when subjects exerted voluntary force to each target force at various speeds. On 27 motor units of AP and 28 motor units of FDI, ramp RTF and ballistic RTF were compared. Furthermore, RTF changes of motor units with the different force speeds were investigated. It is clear that the RTF of the motor units during ballistic contractions were lower than those during ramp contraction. The processes of motor unit RTF changes were classified into 3 types: RTF of type I motor units were relatively low and decreased slightly even when force speed increased widely; RTF of type II motor units were relatively high and decreased irregularly; and RTF of type III motor units, which appeared rarely, decreased their relatively high RTF with increases of force speed increment. It is suggested that the volitional outflow related with the force speed change to the spinal motor pool might cause the different RTF change effects in the various motor units.

CALCIUM UPTAKE BY AXON TERMINALS OF RAT NEUROHYPOPHYSIS AT REST AND DURING MEMBRANE DEPOLARIZATION

1) Uptake and localization of 45Ca were investigated in the isolated rat neurohypophysis by means of electron microscope autoradiography. The gland was incubated in 45Ca-Lockes solution in which 1/10-1/20 of CaCl2 was replaced by 45CaCl2. The emulsion film was developed by a special method to obtain extremely fine silver grains and the number of grains struck by β-particles from 45Ca was counted in photographs of various parts of the tissue.2) In the gland incubated in 56 mM K-45Ca-Lockes solution or stimulated by electrical pulses at 20Hz for 5min, 20-40 grains/mm2 were found in the fibers, whereas only 4-6 grains/mm2 were found in the control.3) In 23 fibers depolarized by excess K (678 grains) and 18 fibers stimulated electrically, 50-60% of the grains were found on the granule membrane or within it. Less than 5% of the grains were found on the nerve membrane and in the mitochondria.4) The conclusion is that 45Ca uptake of neurosecretory nerve fibers is increased by depolarization and that more than half the 45Ca entering a fiber moves to the membrane of the neurosecretory granules or into the granules themselves.

Variation of amount of muscle discharges during ballistic isometric voluntary contraction in man

The effect of force velocity on the relation between voluntary force exertion and amount of muscle discharge was investigated. Surface e.m.g. from the adductor pollicis muscle and voluntary force curve were recorded simultaneously. Examined forces were selected from 500 to 3500 g at the peak force (about 30% of MVC) with time to peak of force curve between 60 ms and 500 ms. The amount of discharge during slow ramp contraction increased with the force increment. In ballistic contractions there was a wide variation in both the amount and rate of discharge. It is suggested that the modes of motor unit activities are different between force exertion with time to peak of less than 150 ms and force exertion with time to peak of over 150 ms.

An analysis of frequency response of motor units during voluntary isometric contractions at various speeds

To ascertain the differences in discharge properties of a hand muscle between ramp and ballistic contractions, firing frequencies of 48 motor units of adductor pollicis muscle were analyzed during 3-kg isometric voluntary contractions at various force speeds. The force exertions were classified into 3 degrees: slow ramp, fast ramp, and ballistic contractions. The instantaneous frequencies (IFs) of motor units increased gradually when the force exertions were progressed to the target in slow and fast ramp contractions. The slopes of the linear regression equations between IFs and force levels were almost all constant during slow ramp contractions and were scattered slightly during fast ramp contractions. However, the slopes during ballistic contractions scattered widely. The y-intercepts of the same regression lines increased slightly with respect to the increment of force speed when slow and fast ramp contractions were performed. However, a remarkably wide variation of the y-intercepts was observed during ballistic contractions. Motor units could be fired at high frequencies at the beginning of discharge when ballistic contractions were performed as compared with slow and fast ramp contractions.