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Biomedical subjects

T Sadoyama

Publications and source records attributed to T Sadoyama.

At least 19 recordsLinked to original sources
PubMed2001

Influence of contraction force and speed on muscle fiber conduction velocity during dynamic voluntary exercise.

Before using electromyographic (EMG) variables such as muscle fiber conduction velocity (MFCV) and the mean or median frequency (MDF) of an EMG power spectrum as indicators of muscular fatigue during dynamic exercises, it is necessary to determine the influence of a joint angle, contraction force and contraction speed on the EMG variables. If these factors affect the EMG variables, their influence must be removed or compensated for before discussing fatigue. The vastus lateralis of eight normal healthy male adults was studied. EMG signals during non-fatiguing dynamic knee extension exercises were detected with a three-bar active surface electrode array. EMG variables were calculated from the detected signals and compared with the angle of the knee joint, the extension torque and the extension speed. The extension torque was set at four levels with 10% intervals between 40 and 70% of the maximum voluntary contraction. The extension speed was set at five levels with 60 degrees /s intervals between 0 and 240 degrees /s. Because the joint angle unsystematically affected the MFCV, EMG variables at a given joint angle were extracted for comparison. The influence of the extension torque and speed on the extracted EMG variables was clarified with an ANOVA and a regression analysis. The statistical analyses showed that MFCV increased with the extension torque but did not depend on the extension speed. In contrast, MDF was independent of the extension torque but was dependent on the extension speed. MDF thus showed a behavior different from that of MFCV. It became clear that if MFCV is used as an indicator of muscular fatigue during dynamic exercises, it is at least necessary to extract MFCV at a predetermined joint angle and then remove the influence of extension torque on MFCV.

Action Potentials↗
PubMed1999

Changes in surface EMG parameters during static and dynamic fatiguing contractions.

The effect of contraction types on muscle fiber conduction velocity (MFCV), median frequency (MDF) and mean amplitude (AMP) of surface electromyography was examined in the vastus lateralis of 19 healthy male adults. The subjects performed knee extension both statically and dynamically until they were exhausted. The static contraction was a sustained isometric extension of the knee at a joint angle of 90 degrees with 50% of the maximum voluntary contraction (MVC) load. The dynamic contraction was a repetitive isotonic extension of the knee between the angles of 90 degrees and 180 degrees with the same 50% MVC load at a frequency of 10 times per minute. MFVC during the static contraction significantly decreased during the exercise (p < 0.01). On the other hand, MFVC during the dynamic contraction did not significantly change throughout the exercise. MDF decreased and AMP increased during both types of contractions (p < 0.01). Because the blood flow within the muscle is maintained during the dynamic contraction by enhanced venous return from the contracting muscle, these results suggested that MFVC is affected by the metabolic state in the muscle and the changes in MDF cannot be explained only by that of MFVC.

Adult↗
PubMed1993

[Muscle fiber conduction velocity in right and left biceps brachii for badminton players].

The purpose of this study was to investigate the laterality of muscle fiber conduction velocity in biceps brachii for badminton players, who have stronger arm in the handedness side for long term training. The muscle fiber conduction velocity was calculated from the propagation time of the action potentials along the muscle fibers and the electrode separation using cross-correlation method. For badminton players, significant lateral differences (e.g. right side skillful) were observed in the upper arm girth (P < 0.01) and isokinetic peak torque at 0, 10, 20, 30, 40 rpm (P < 0.01). For control subjects, significant lateral differences were in upper arm girth (P < 0.05) and isokinetic peak torque at exactly 30 rpm (P < 0.05). As for muscle fiber conduction velocity, there were no statistically significant differences between right (4.16 +/- 0.34 m/sec) and left (4.08 +/- 0.34 m/sec) sides in badminton players, and the control group exhibited same tendency (right: 4.36 +/- 0.25 m/sec, left: 4.28 +/- 0.33 m/sec) as well. These results suggest no training-induced change in the muscle fiber conduction velocity.

Adult↗
PubMed1989

Processing of myoelectric signals for estimating the location of innervation zones in the skeletal muscles.

An electrical activity associated with the excitement of muscle fibers arises from the myoneural junctions located at the middle length of the fibers and propagates to the both ends. This propagation can be detected with a multi-electrode array placed on the skin surface. Therefore, the position of the myoneural junctions, or of the innervation zones as a collection of myoneural junctions, can be estimated from the source of the propagation. The authors propose a method for determining the position of the propagation sources automatically with a computer. The method was based on the line-source model of muscle fibers. The positions of the propagation sources were treated as parameters in the model. When some values are assigned to the parameters, the surface potentials are calculated from the currents assumed to propagate on the muscle fibers. The computer searched for the optimal parameters which gave the best fit between the calculated and the measured potentials on the skin surface. Using this method some separate sources of propagation were detected at the middle length of the biceps brachii. The activity of the individual innervation zones was quantitatively described by the average amplitude of the potentials arising from the corresponding sources. This description clarified the changes in the activity of innervation zones when the contraction forces were varied.

Action Potentials↗
PubMed1988

Fibre conduction velocity and fibre composition in human vastus lateralis.

The relationship between muscle fibre composition and fibre conduction velocity was investigated in 19 male track athletes, 12 sprinters and 7 distance runners, aged 20-24 years, using needle biopsy samples from vastus lateralis. Cross sectional areas of the fast twitch (FT) and slow twitch (ST) fibres were determined by histochemical analysis. The percentage of FT fibre areas ranged from 22.6 to 93.6%. Sprinters had a higher percentage of FT fibres than distance runners. Muscle fibre conduction velocity was measured with a surface electrode array placed along the muscle fibres, and calculated from the time delay between 2 myoelectric signals recorded during a maximal voluntary contraction. The conduction velocity ranged from 4.13 to 5.20 m.s-1. A linear correlation between conduction velocity and the relative area of FT fibres was statistically significant (r = 0.84, p less than 0.01). This correlation indicates that muscle fibre composition can be estimated from muscle fibre conduction velocity measured noninvasively with surface electrodes.

Adult↗
PubMed1987

Temporal relationships of EMG changes preceding voluntary movement to premovement cortical potential shifts.

The silent period and a rhythmic slower wave in EMG appear preceding a rapid voluntary movement (Tanii 1984). The present study was performed to investigate temporal relationships of the EMG changes preceding movement to premovement cortical potential shifts, in order to clarify whether the EMG changes are related to preparation and initiation of voluntary movement. A strong push of a hard band with the right wrist was conducted rapidly following a slightly sustained contraction. The surface EMG was detected from the right triceps brachii muscle. The EEG was recorded from C3, Cz and C4. Slowing of the EMG occurred before the movement in addition to the slower wave. The EMG slower waves were accompanied by a negative deflection of raw EEG potentials. The averaged cortical potentials preceding movement fell into 3 negative potentials. The first potential started about 1.0 sec before the EMG burst. Many of the EMG slower waves occurred in the phase of the second potential occurring 330-510 msec before the EMG burst. Premovement silent period appeared in the phase of the third potential occurring 30-60 msec before the EMG burst. Amplitude of these potentials was larger in the contralateral hemisphere than in the ipsilateral one. This asymmetry became statistically significant in the phase of the second potential. The results suggest that the EMG slower waves and the premovement silent period are associated with preparation and initiation of voluntary movement.

Adult↗
PubMed1987

Skeletal muscles from which the propagation of motor unit action potentials is detectable with a surface electrode array.

Motor unit action potentials (MUAPs) propagate bidirectionally along the muscle fibers. Whether or not the propagation of MUAPs can be detected with surface electrodes depends on the configuration of muscle fibers and innervation zones. The authors clarified the muscles from which the propagation of MUAPs is detectable with a surface electrode array placed along the muscle fibers. Twenty-six typical muscles in the arm, leg, trunk, neck and face were investigated under voluntary contraction, and in 19 muscles the propagation of MUAPs was detected. In these muscles the source of the bidirectional propagation marked the position of innervation zones. In the other 7 muscles, the propagation of MUAPs was not detected or was detected only under weak contraction.

Action Potentials↗
PubMed1987

Changes of the average muscle fiber conduction velocity during a varying force contraction.

The average conduction velocity of muscle fibers measured with a surface electrode has been reported to increase with the level of contraction force. To clarify the factors causing this increase, the authors decomposed the interference surface EMG signal into its constituent motor unit action potentials and compared the average conduction velocity with the conduction velocity measured at the individual discharges of motor units. The conduction velocity within individual motor units increased with the contraction force and contributed to the increase of the average conduction velocity. However, the increase of the conduction velocity within motor units was relatively small and was insufficient to cause the increase of the average conduction velocity. This result indicates that the motor units recruited at higher thresholds of force should have higher conduction velocities.

Adult↗
PubMed1986

The propagation of single motor unit action potentials detected by a surface electrode array.

Propagation of single motor unit action potentials (MUAPs) was detected by surface electromyography. Sixteen EMG signals were simultaneously recorded by a linear bipolar electrode array placed along the longitudinal axis of the biceps brachii. EMGs were obtained from 8 healthy adults at 10-40% of the maximum contraction. Single MUAPs were extracted by superimposing and averaging the EMG signals at the timing of potential peaks. Most MUAPs were triphasic and propagated symmetrically in opposite directions from the middle length of the muscle to the tendons. Some MUAPs showed more than 5 phases and asymmetrical wave forms on the proximal and distal recording sites. The asymmetrical wave forms were assumed to be caused by the scatter of myoneural junctions and by the time delay of the excitation at the junctions. The position of the myoneural junctions on muscle fibers was estimated from the source of propagation. The innervation zone of individual motor unit was found to spread up to 14 mm in the muscle fiber directions.

Action Potentials↗
PubMed1985

A surface electrode array for detecting action potential trains of single motor units.

Action potentials of single motor units were detected by a linear surface electrode array placed perpendicular to the longitudinal axis of the biceps brachii. Twelve myoelectric signals were derived simultaneously from a voluntarily contracting muscle. Using a visual feedback control, 3 subjects produced spike trains of single motor unit action potentials (MUAPs) at a weak contraction. When the myoelectric signals showed an interference pattern at a moderate contraction, several MUAPs were isolated by a visual analysis. MUAPs occurring at about fixed intervals with constant amplitudes and with identical wave forms were presumed to be the action potential trains of single motor units. Reliable estimates of single MUAP wave forms were obtained by averaging and superimposing the detected signals at a timing of characteristic potential peaks. Then not only the firing rate of the spikes but also the territory and the wave form of single MUAPs were investigated. Most MUAPs had a sharp and symmetrical distribution of potentials on a skin surface along the muscle circumference, while some MUAPs showed complex wave forms with some separate potential peaks. The possible arrangement of muscle fibers belonging to the motor units was estimated from the MUAP wave forms.

Action Potentials↗
PubMed1985

Power spectral analysis of the surface electromyogram before and after a warning signal in a reaction movement.

The present study was performed to substantiate the premise that frequency components of the surface EMG before a reaction movement change after a warning signal (S1). Twelve subjects extended rapidly the trunk from a bent position in response to a moving signal (S2) 2 sec after S1. The movement was repeated 20 times. Bipolar surface EMG recordings were made from the erector spinal muscle. A minicomputer calculated power spectra of the surface EMGs for 2 sec before S1 and for 2 sec from S1 until S2 in each trial. From each spectrum, the mean frequency (MF) was calculated. EMG itself was examined. Statistical comparisons of differences between the mean values of the MF before and after S1 showed that a significant difference was found in 5 subjects. For the subjects, the mean value of the MF after S1 was a lower value than that of the MF before S1. Increase of EMG power in frequency range from 30 to 50 Hz was observed in the averaged EMG spectrum after S1 in the subjects. Slowing of the surface EMG during the preparatory period from S1 until S2 was often observed in the subjects. These results show that the power spectrum of the surface EMG after S1 shifted to lower frequencies and suggest that the EMG spectral shift is due to the slowing of the surface EMG in association with motor preparation to perform the movement.

Electromyography↗
PubMed1983

The distribution of myoneural junctions in the biceps brachii investigated by surface electromyography.

The location of the myoneural junction was investigated by a surface electromyogram. During a voluntary muscular contraction, an electrode array was placed on the skin overlying the muscle to detect myoelectric potentials propagating in both proximal and distal directions along the muscle fibers. The source of the propagating waves was presumed to mark the location of the myoneural junctions. The recordings were repeated to cover the whole muscle surface and the distribution of myoneural junctions was determined. Myoneural junctions in the biceps brachii were located nearly at the middle length of the muscle and were distributed in a zone across the muscle. The distribution showed differences in 3 subjects examined. In 1 subject, myoneural junctions occupied a single zone, while the other 2 subjects had 2 parallel zones separated by 10-20 mm. This information about the location of myoneural junctions is important for determining the electrode position in an electromyogram study.

Adult↗
PubMed1983

The propagation of motor unit action potential and the location of neuromuscular junction investigated by surface electrode arrays.

A myoelectric signal was recorded from the biceps brachii muscle using surface electrode arrays which consisted of 15 pieces of stainless steel wire placed parallel to each other with 5 mm interelectrode spacing. The electrode assembly was positioned parallel to the underlying muscle fibers and amplifiers were connected bipolarly to 11 pairs of adjacent electrodes. In the chart of recorded signals a propagation of the action potential was observed, originating from a neuromuscular junction and traveling both in the proximal and distal directions. In one recording under an isotonic and isometric contraction condition, two neuromuscular junctions were found to be active. One was located approximately at the center of the muscle and the other was 15 mm distal from it. It was found that the amplitude of the myoelectric potential originating from the distal neuromuscular junction increased gradually during a 1 min heavy muscular loading (50% maximum voluntary contraction).

Action Potentials↗
PubMed1981

Frequency analysis of surface EMG to evaluation of muscle fatigue.

A theory concerning the spectral density of surface electromyogram (EMG) in isometric contraction is described and herein, a conduction velocity measure, which was derived from a surface EMG model, is suggested. In order to confirm the validity of this measure, the spectral modification with respect to muscle fatigue is studied experimentally. The EMG signals were obtained from the biceps brachii and the rectus femoris in four subjects. The spectral modification shifted to a lower frequency as fatigue developed. The conduction velocity measure decreased linearly in both the biceps brachii and rectus femoris, but this tendency was more pronounced in the biceps. It is suggested that the spectral shift was concerned with conduction velocity of action potential along the muscle fibres. From these experimental results, we believe that we are justified in claiming that our conduction velocity measure is a useful index to estimate motor function.

Action Potentials↗