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A Review of the Technologies and Methodologies Used to Quantify Muscle-Tendon Structure and Function
Published in Cornelius Leondes, Musculoskeletal Models and Techniques, 2001
Rate coding and recruitment are neural activation characteristics that can regulate muscle force production. Force transducers, neural stimulators, and recording electrodes are the common instruments used to investigate these neural factors although some chemical techniques have also been employed.3,37,56,64,66,81,92,100 The effect of rate coding has been investigated by stimulating a muscle at different frequencies via its nerve and recording the force developed. Voluntary contractions have also been performed with recording electrodes used to monitor the stimulation frequency over time. The effects of recruitment and the order of motor unit recruitment have been investigated by placing small electrodes within a muscle and recording the electrical activities of single motor units as a person voluntarily contracts the muscle and generates increasingly greater force. Motor units are activated and deactivated in a specific order.100 The idea of a rank order of recruitment has been supported in several other studies.18,49,50,61
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.
Hamstring Muscle Stiffness Affects Lower Extremity Muscle Recruitment and Landing Forces during Double-Legs Vertical Jump
Published in Sports Biomechanics, 2023
Amornthep Jankaew, Yih-Kuen Jan, Ing-Shiou Hwang, Li-Chieh Kuo, Cheng-Feng Lin
Evidence exhibits the linear relationship between the frequency spectrum of electromyography and its motor unit recruitment. The processing of the frequency analysis provides essential information related to the active motor unit recruitment through an increase in the recruitment rate and firing rate (Moritani & Muro, 1987). Increased mean and median sEMG frequency domains result in greater motor unit action potential reflecting a greater capability of muscle force production during short-duration muscle contractions (Solomonow et al., 1990). The strength of the current study is the use of the median frequency analysis of lower limb muscles to elicit motor unit action potentials during jumping manoeuvres. Greater recruitment of the lateral hamstrings and quadriceps, both medial and lateral parts, during the SSC of the standing vertical jumps were demonstrated in the high-stiffness group compared to the low-stiffness counterpart with moderate to large effect sizes. This could potentially be explained by the neuromechanical adaptation of a stiff muscle, noting that the nervous system has reacted to active muscles that have the characteristics of activation and deactivation dynamics to produce efficient or effective workings of recurring movements (Neptune & Kautz, 2001). Theoretically, the modification of activation levels relies on the concerted actions of the Golgi tendon reflex and stretch reflex, resulting in increased neural drive to a muscle through the neural pathways (Zatsiorsky et al., 2021). Individuals with greater hamstring stiffness can superiorly modify the recruitment of the hamstring and associated muscles than counterparts through the facilitation of the myotatic reflex and inhibition of the Golgi tendon reflex. The results indicate that athletes with similar hamstring strength but greater stiffness contribute substantially to the activation level of muscular contraction so as to increase energy storage capacity and warrant muscular strain resistance for a given applied load in the SSC. The study is also in agreement with Schmidtbleicher et al. (1988), who found a reduction of muscle activity in 50–100 ms before ground contact in an untrained population with low muscle tension. Additionally, higher stiffness of the hamstring did not hamper the recruitment of the antagonistic muscles, such as the quadriceps. In turn, we observed greater recruitment of antagonist or other related agonist muscles in this study sample. This mirrors increased knee stiffness, which largely depends on the antagonistic co-contraction of the knee flexor and extensor at the preparation phase for ground impact (Hortobágyi & DeVita, 2000). Thus, it is important to note that maintaining the stiffness of the passive and active structures of the hamstring is warranted for recruitment modulation of the lower limb during the SSC function.