Tadashi Masuda

Bio: Tadashi Masuda is an academic researcher from Japanese Ministry of International Trade and Industry. The author has contributed to research in topics: Motor unit & Electromyography. The author has an hindex of 16, co-authored 24 publications receiving 1326 citations.

The Position of Innervation Zones in the Biceps Brachii Investigated by Surface Electromyography

Abstract: A linear surface electrode array placed along the muscle fibers detects motor unit action potentials propagating bilaterally to the tendons. The location of the propagation source is presumed to mark an innervation zone. We developed a computer program, which automatically determined the potential source by applying a correlation calculation and a linear regression to the recorded signals. The spacing between the contacts in the electrode array was 5.0 mm, whereas for some recordings the histogram indicating the position of estimated source had a sharp peak concentrated in a 1.0 mm area. In the biceps brachii some subjects were found to have two innervation zones separated by 10-20 mm. The peaks corresponding to the innervation zones differentially changed their histogram scores according to the contraction force. We also constructed an electrode assembly, which had four columns of the linear electrode arrays, and clarified the distribution of the innervation zones in the biceps brachii.

Innervation zones of the upper and lower limb muscles estimated by using multichannel surface EMG.

Abstract: The distribution of innervation zones was investigated in 3 subjects for 17 muscles and 8 muscle groups in the upper and lower limb, by detecting bi-directional propagation of motor unit action potentials (MUAPs) with the multichannel surface electrode array. Clarification of the distribution of innervation zones depended on the ease in detecting the propagation of MUAPs and the actual scattering of innervation zones, which were closely related with muscle morphology with respect to the arrangements of muscle fibers. In muscles having fibers running parallel to each other, such as the biceps brachii, intrinsic hand muscles, vastus lateralis and medialis, tensor fasciae latae, peronei, soleus, tibialis anterior, and hypothenar muscles in the foot, it was relatively easy to detect the propagating MUAPs, and the innervation zones were distributed in a relatively narrow band around muscle belly. On the other hand, in muscles with a complicated structure including pinnation of muscle fibers, in-series muscle fibers and aponeurotic tissues, such as the deltoid, flexors and extensors in the forearm, rectus femoris, sartorius, hamstrings and gastrocnemius, it was more difficult to detect the propagating MUAPs and to identify the innervation zones, which were widely scattered or distributed in complex configurations. The distribution of the innervation zones clarified in the present study can be used to find the optimal location of electrodes in surface EMG recordings and of stimulus electrodes in the functional and therapeutic electrical stimulations. It may also be useful in motor point biopsy for diagnosis of neuromuscular diseases as well as in the botulinum toxin injection for the treatment of spasticity.

The extraction of neural strategies from the surface EMG

Abstract: This brief review examines some of the methods used to infer central control strategies from surface electromyogram (EMG) recordings. Among the many uses of the surface EMG in studying the neural control of movement, the review critically evaluates only some of the applications. The focus is on the relations between global features of the surface EMG and the underlying physiological processes. Because direct measurements of motor unit activation are not available and many factors can influence the signal, these relations are frequently misinterpreted. These errors are compounded by the counterintuitive effects that some system parameters can have on the EMG signal. The phenomenon of crosstalk is used as an example of these problems. The review describes the limitations of techniques used to infer the level of muscle activation, the type of motor unit recruited, the upper limit of motor unit recruitment, the average discharge rate, and the degree of synchronization between motor units. Although the global surface EMG is a useful measure of muscle activation and assessment, there are limits to the information that can be extracted from this signal.

Myoelectrical manifestations of localized muscular fatigue in humans.

Abstract: Fatigue may be described as the decline in the ability of an individual to maintain a level of performance. However, the issue of fatigue in man is complex due to the various physiological and psychological phenomena which contribute to it. This article is limited to a discussion appertaining to that fatigue associated with changes in the physiological processes, and specifically that which is caused by sustained or repeated muscle contractions. It has long been known that during muscle contractions the frequency spectrum of the myoelectric signal undergoes a shift. Recently, several analyses and investigations have been reported on the applicability of this phenomenon for supplying objective or noninvasive measurements of localized muscle fatigue. The essence and results of pertinent publications are discussed with emphasis on the relationship between the spectral shift of the myoelectric signal, conduction velocity of muscle fibers, pH of the interstitial fluid and blood flow within a muscle.