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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
The primary functions of MS are associated with muscle contraction length–velocity characteristics (84, 109, 127, 137). These characteristics can be summarized as follows: The MS allows the extrafusal fibers to contract at appropriate force levels when the resistance encountered is altered either during a contraction or between successive contractions.Fatigue induced drops in muscle contraction force (and velocity) can be partially compensated for by a stretch reflex.The MS function has servo-assist characteristics which allow the brain to create voluntary muscle contraction with less energy expenditure.Appropriate use of the stretch-shortening cycle can create a stretch reflex that can augment concentric muscle force.
Functional Neurology
Published in James Crossley, Functional Exercise and Rehabilitation, 2021
Stretch-reflexes contribute to power and efficiency, especially in movements involving a stretch-shortening cycle, such as walking, running or swimming. A stretch-shortening cycle involves: An eccentric ‘pre-load’Isometric stabilizationForce ‘transformation’Stretch reflexConcentric force productionTo feel how much a pre-load supports movement, try standing next to a wall and then jumping as high as you can. You will intuitively bend the knees and swing the arms down, pre-loading fascial chains. Now repeat, but this time start at the bottom of the knee bend. See how much jump height decreases without dynamic ‘pre-load’.
Throwing
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
The preparation phase provides a longer pulling path for accelerating the arm and serves to pre-stretch the musculature. The movements of the preparation phase are initiated by a forceful contraction of the prime movers for each action (concentric contraction). If a run-up is used before the throw, this will help to create momentum within the body and make the preparatory movements faster and require less muscular effort to initiate. As the body reaches the end position of the preparation phase, the rotator muscles of the trunk become stretched and the stretch reflex stimulates an eccentric contraction. Similarly, the muscles of the anterior shoulder region become stretched by the abduction and horizontal extension of the shoulder. These eccentric contractions facilitate the use of the stretch–shortening cycle to enhance the force of the early preparation phase and thus increase the velocity of the movement.
Effectiveness of Physical Therapy Interventions in Children with Brachial Plexus Birth Injury: A Systematic Review
Published in Developmental Neurorehabilitation, 2023
Mariana Aguiar de Matos, Deisiane Oliveira Souto, Bruno Alvarenga Soares, Vinícius Cunha de Oliveira, Hércules Ribeiro Leite, Ana Cristina Resende Camargos
Plyometric training associated to conventional physical therapy was also reported in our systematic review.24 Plyometrics refer to exercises involving the stretch shortening cycle, that is, a quick stretching of the musculature followed by a fast-concentric action. Plyometric movement requires fewer motor units and less oxygen utilization to gain strength compared to concentric or eccentric contractions. This allows the recruitment of additional motor units to produce more strength and makes the muscles more resistant to fatigue.32 The additional effect of this intervention promoted similar benefits to the conventional physical therapy intervention, but the percentage of improvement was greater for active range of motion and muscle strength in children from 3–6 years with Erb’s palsy.24 Many plyometric movements resemble those found in typical children’s play33 and add fun to children who tend to dislike prolonged periods of monotonous training.34
Lower Limb Joint Functions during Single-Leg Hopping in-Place in Children and Adults
Published in Journal of Motor Behavior, 2022
At the preferred hopping frequency, children demonstrated a primary function equally between spring and strut at the knee (Figure 3b). Chronological age and sex appeared to have limited influence on the selection of primary knee function. Likely, chronological age is an insufficient factor due to its disassociation with maturation (De Ste Croix et al., 2021). Utilizing the knee as a strut might be beneficial by reducing the degrees of freedom for the movement (Bernstein, 1967) and enabling better transfer of energy from the ankle to the knee and above (Qiao & Jindrich, 2016). However, greater spring function would suggest an advanced capacity to transition from eccentric to concentric muscle contractions to generate the work required for upward movement during hopping (De Ste Croix et al., 2021). The transition from strut to spring in children might indicate an improvement of stretch-shortening cycle function at the knee. Moreover, considering the knee has been shown to be used as a damper during running in young adults (Qiao & Jindrich, 2016) and the musculotendon architecture might optimize energy absorption (Qiao, 2021), it is plausible that subjects that hopped with a primary strut function have difficulties dissipating energy appropriately at the knee joint. Therefore, determining knee joint function during preferred single-leg hopping might provide some insight to injury risk associated with increased knee joint quasi-stiffness.
Force-length-velocity behavior and muscle-specific joint moment contributions during countermovement and squat jumps
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
The countermovement (CMJ) and squat (SJ) jump are common tasks used to assess and monitor neuromuscular performance of the lower extremity muscles (McGuigan et al. 2006; van Hooren and Zolotarjova 2017). During the CMJ an athlete begins in a standing position, initiates a countermovement in the downward direction, eventually reverses movement directions in the upward direction, and attempts to jump as high as possible. During the SJ an athlete begins in a squat position, initiates movement in the upward direction without any countermovement, and attempts to jump as high as possible. Therefore, the major difference between the tasks/jumps is that the CMJ includes an eccentric contraction that precedes the concentric contraction, whereas the SJ only includes a concentric contraction. Given the absence of an eccentric contraction during the SJ, the difference between the CMJ and SJ is often used to evaluate the performance of the stretch-shortening cycle or the utilization of the eccentric phase during jumping tasks (Bosco et al. 1982; Finni et al. 2000; van Hooren and Zolotarjova 2017).