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Stimulation of Excitable Tissue and Sensory Stimulators
Published in Leslie A. Geddes, Handbook of Electrical Hazards and Accidents, 1995
The skeletal muscle response to a single stimulus is called a twitch; the response to a train of stimuli is called a tetanic contraction or tetanus. As the frequency of the stimuli is increased from say 1/sec, the twitches become closer and fuse into a tetanic (sustained) contraction; Figure 2.10 shows such a sequence. Note 1) that in this muscle, above about 10/sec the individual twitches have fused and 2) above about 30/sec, the force of the tetanic contraction does not increase, 3) the force developed by a tetanic contraction is much greater then that for a twitch and 4) the duration of a tetanic contraction persists as long as the stimulus train is delivered, providing muscle metabolism can be sustained. Tetanic stimuli applied directly to a motor nerve produce a very strong muscle contraction. The response to power-line current (50-60 Hz) is a tetanic contraction of skeletal muscle, the contraction persisting as long as the current flows.
Biomechanical Modeling of Muscular Contraction
Published in Yuehong Yin, Biomechanical Principles on Force Generation and Control of Skeletal Muscle and their Applications in Robotic Exoskeleton, 2020
Active forces at different frequencies are shown in Figure 2.34. A twitch contraction takes place at frequency 1 Hz, the muscle force first increases then decreases to zero. The dwell time is about 50 ms, longer than the time of Ca2+ concentration. This phenomenon is due to the process of Ca2+ binding to Tn and myosin motors attaching to thin filament. If the frequency continues to increase, summation of muscle contraction will happen. With a high frequency of 500 Hz, the muscle reaches the peak force, resulting in a tetanic contraction.
Blood perfusion changes during sacral nerve root stimulation versus surface gluteus electrical stimulation on in seated spinal cord injury
Published in Assistive Technology, 2019
Liang Qin Liu, Martin Ferguson-Pell
In theory, all muscles consist of a number of motor units, and the fibers belonging to a motor unit are dispersed and interlink among fibers of other units. A motor unit normally consists of one motor neuron and all of the muscle fibers it stimulates. The muscle fibers belonging to one motor unit can be spread throughout a part, or most of the entire muscle, depending on the number of fibers and size of the muscle. When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contracted. The activation of single motor neuron results in a weak distributed muscle contraction (twitch contraction). In contrast, the activation of more motor neurons will result in more muscle fibers being activated, and therefore, a stronger muscle contraction (tetanic contraction) was produced. The higher the recruitment of motor unit, the stronger the muscle contraction will be. The activation of more motor neurons will result in more muscle fibers being activated, and therefore, a stronger muscle contraction (Guyton & Hall, 0000). In comparison, between sacral nerve root stimulation versus traditional surface FES of gluteal muscles, the larger numbers of motor neurons recruitment in sacral nerve roots stimulation may produce stronger contraction than surface FES. Therefore, it can activate gluteus muscles more efficiently. Sacral nerve root stimulation can efficiently activate all motor neurons that innervate gluteal maximus, whereas surface FES of gluteus maximus may be limited by the size of electrodes and the depth of electrical signal to reach the muscle motor points.