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Key human anatomy and physiology principles as they relate to rehabilitation engineering
Published in Alex Mihailidis, Roger Smith, Rehabilitation Engineering, 2023
Qussai Obiedat, Bhagwant S. Sindhu, Ying-Chih Wang
There are two strategies that a muscle uses to increase muscular force output: recruitment coding and rate coding. Recruitment coding means “sequence of motor unit activation.” Muscles produce higher forces by following the size principle. That is, smaller motor units are recruited first, and successively larger motor units are recruited as the force requirement increases (Astrand and Rodahl 1977; Milner‐Brown, Stein, and Yemm 1973a; Edgerton 1978). Rate coding means “frequency of motor neuron firing” which represents how frequently the motor units are activated by the nervous system. As the firing rate of the motor unit increases, it produces an increasing amount of muscular force (Astrand and Rodahl 1977; Milner‐Brown, Stein, and Yemm 1973a; Milner‐Brown, Stein, and Yemm 1973b; Edgerton 1978).
Electromyogram
Published in Kayvan Najarian, Robert Splinter, Biomedical Signal and Image Processing, 2016
Kayvan Najarian, Robert Splinter
If the electric activities of a specific motor unit (or only a few motor units) are to be measured, subcutaneous concentric EMG needle electrodes are used for measurement. In such EMG recordings, electrodes incorporated in very fine needles can be inserted in the muscle itself. These electrodes record the electric potential generated by the depolarization of the muscle cells directly surrounding the needle electrode. More specifically, in such neuromuscular measurements, the electric activity of a single motor unit is directly measured. When a needle has more than one electrode, bipolar measurements can be made to derive potential gradients within the muscle. Figure 11.6 illustrates the different phases of electrode placement. During needle insertion, illustrated in Figure 11.6a, there is a short burst of activity. When an axon of a nerve is touched, there may be several repetitions of bursts of activity. The transition from rest to various stages of activity shown in Figure 11.6b is characterized by the frequency of the measured potentials.
A Review of the Technologies and Methodologies Used to Quantify Muscle-Tendon Structure and Function
Published in Cornelius Leondes, Musculoskeletal Models and Techniques, 2001
The level of force generated by voluntary contraction of skeletal muscle is controlled by at least two neural mechanisms, motor unit recruitment and modulation of the firing rate of active motor units (rate coding). It is generally accepted that motor units are recruited in an orderly manner consistent with the size principle of Henneman et al.64,65 According to Henneman, the excitability or threshold level at which a motor unit is recruited is inversely related to the diameter of the motoneuron. Thus the participation of a motor unit in graded motor activity is dictated by the size of its neuron. It appears that slow fibers are innervated by small, low threshold, slow conducting motor nerves. Fast fibers are innervated by larger, higher threshold, faster conducting motor nerves. Thus, slow fibers are recruited first, followed by fast fibers. Studies conducted by other researchers have supported this finding.3,18,30,49,50,61 Rate coding allows force regulation through summation of the force developed by single twitches. There is a frequency of stimulation above which twitch responses become fused and fibers generated their maximal force. Below the fusion frequency, fibers generate submaximal forces which vary relative to the stimulation frequency.18,67
Electromyographic responses of knee isokinetic and single-leg hop tests in athletes :dominant vs. non-dominant sides
Published in Research in Sports Medicine, 2022
Ali Kerim Yılmaz, Menderes Kabadayı
In addition to evaluating the muscle strength and functions produced by the extremities during specific joint movements, the assessment of the muscles activations involved in the generation of strength at the time of movement by electromyographic (EMG) methods is essential for monitoring both the kinematic structure of movement and the acute and chronic changes occurring in the muscles due to exercise or regular training. Thanks to EMG evaluation, it is possible to control the neuromuscular functions of the movement and learn more about the properties of motor units (Christie et al., 2009). In addition, EMG signals are an indicator of the transmission rate emerging in muscle fibres and a sign of neural stimulation (Wang et al., 2015). EMG signals can be detected in two different ways: surface (sEMG) and needle electrode. However, in determining the movement potentials of the skeletal muscle, sports scientists prefer sEMG, which is adhered to the skin surface and is easier to apply (Lepley et al., 2012; Roca-Dols et al., 2016; Vigotsky et al., 2018).
The effect of electrical muscle stimulation on quadriceps muscle strength and activation patterns in healthy young adults
Published in European Journal of Sport Science, 2021
Yuichi Nishikawa, Kohei Watanabe, Tetsuya Takahashi, Noriaki Maeda, Hirofumi Maruyama, Hiroaki Kimura
It is widely known that electrical muscle stimulation (EMS) interventions can improve muscle performance and muscle thickness (Belanger, Stein, Wheeler, Gordon, & Leduc, 2000; Hirose et al., 2013; Maffiuletti, Minetto, Farina, & Bottinelli, 2011; Nishikawa et al., 2019; Stein et al., 2002; Stevens, Mizner, & Snyder-Mackler, 2004). The previous studies speculated that the EMS intervention induced non-physiological recruitment order and synchronous discharge of motor units (Gregory & Bickel, 2005; Jubeau, Gondin, Martin, Sartorio, & Maffiuletti, 2007; Sheffler & Chae, 2007). In general, according to the size principle, voluntary motor unit recruitment describes the progressive recruitment of small, typically slow motor units followed in order of increasing size to the large, typically motor units (Henneman, 1957; Henneman, Somjen, & Carpenter, 1965). However, EMS recruits motor units randomly in relation to axon diameter (Major & Jones, 2005). It indicates that muscle activation differs between voluntary and electrically induced contraction.
Comparing the effects of low and high load resistance exercise to failure on adaptive responses to resistance exercise in young women
Published in Journal of Sports Sciences, 2019
D. G. A. Stefanaki, A. Dzulkarnain, S. R. Gray
Based on the size principle motor units, and the muscle fibres they innervate, are recruited progressively based on the force requirements. That is, the smaller, lower threshold motor units that innervate type 1 fibres are recruited first followed by higher threshold motor units, that innervate type 2 fibres (Henneman, 1985). For this reason many studies have hypothesised that to maximise gains in muscle mass and strength heavier loads are required to ensure activation, fatigue and thus hypertrophy of all muscle fibres (Jenkins et al., 2015; Schoenfeld, Contreras, Willardson, Fontana, & Tiryaki-Sonmez, 2014). However, the data generated which purportedly supports this hypothesis is based on the use of surface electromyography (sEMG) data to show a greater muscle activation when lifting heavier loads (Jenkins et al., 2015; Schoenfeld et al., 2014). Interpretation of such data is not straight forward and it cannot be assumed that a higher sEMG amplitude, whilst lifting heavier loads, can be attributed to the recruitment of the complete pool of motor units. The current study and the work of others, in men, indicate that (Mitchell et al., 2012; Morton et al., 2016) whilst, larger motor units may be recruited at heavier loads, when performed to failure a similar level of motor unit activation and thus adaptation occurs regardless of load (Carpinelli, 2008; Fisher et al., 2011). Further work is, however, required to confirm the mechanisms underlying these observations.