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Exercise Selection
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 two primary goals of a strength-endurance phase are to increase an individual’s force production capacity (i.e., work capacity) and task-specific hypertrophy (91). As discussed within Section 8.3 above, multi-joint exercises may have an advantage over single-joint exercises when it comes to motor unit recruitment. Thus, because multi-joint exercises include a greater magnitude of muscle fibers that contribute to the completion of a movement, more muscle fibers will receive a training stimulus for adaptation. Furthermore, these exercises should be performed through a full range of motion to ensure that the necessary musculature is trained to its fullest extent (9, 18, 38, 55). It should be noted that although multi-joint movements will comprise of most exercises programmed within a strength-endurance phase, single-joint exercises may serve as effective supplemental exercises to help further develop musculature that may contribute to an athlete’s performance, posture, or joint stability. This in turn will allow single-joint exercises to isolate specific muscle groups that are less emphasized during multi-joint movements (e.g., dumbbell lateral raise vs. military press).
Muscle
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
Many factors influence the contractile activity of smooth muscle. The strength of contraction of multiunit smooth muscle may be enhanced by the stimulation of a greater number of cells, or contractile units. This mechanism is directly comparable to motor-unit recruitment employed by skeletal muscle. As the number of contracting muscle cells increases, so does the strength of contraction. However, this mechanism is of no value in single-unit smooth muscle. Due to the presence of gap junctions, all the muscle cells in the tissue are activated at once.
The movement systems: skeletal and muscular
Published in Nick Draper, Helen Marshall, Exercise Physiology, 2014
The signal from the CNS, via motor neurons, for a skeletal muscle to contract is very precise. The recruitment of motor units during muscle contraction is far from random, allowing a smooth but steady increase in muscular tension and sustained contractions in the absence of fatigue. Motor unit recruitment follows the size principle. Initially, the smallest motor units containing slow-contracting fibres are activated, followed by the larger motor units, with faster and more powerful fibres, as more tension is required to conduct the movement. As motor units with larger and larger muscle fibres are recruited, the generation of muscular force increases. This order of motor unit recruitment is important as it allows small gradual increases in muscle tension during weak contractions (like those for posture maintenance) and large increases in tension when forceful contractions are required during the vigorous movements involved in many sports.
Effects of whole-body vibration plus hip-knee muscle strengthening training on adult patellofemoral pain syndrome: a randomized controlled trial
Published in Disability and Rehabilitation, 2022
Zhangxiang Wu, Zhi Zou, Jiugen Zhong, Xinbo Fu, Ligen Yu, Jinzhu Wang, Xin Wang, Qianwen Wu, Xiaohui Hou
Similar to muscle resistance training, whole-body vibration (WBV) training is an alternative method of muscle strengthening [15–19]. The WBV vibratory platform can generate vertical vibrations, which can arouse muscle reflex contractions by facilitating homonymous α-motor neurons via tonic vibration reflexes of the muscle spindles [20]. As a result, motor unit recruitment can be enhanced to improve the excitability of muscle spindles [21], thereby promoting muscle strengthening. Furthermore, WBV training can improve muscle balance, power, and function [15–19]. Thus, combining WBV with muscle strengthening may be a more effective method of treating PFPS. Therefore, we designed this study and hypothesized that WBV plus hip-knee muscle strengthening is more efficient in relieving pain and improving function than is hip-knee strengthening alone.
Traces of muscular fatigue in the rectus femoris identified with surface electromyography and wavelets on normal gait
Published in Physiotherapy Theory and Practice, 2022
Alberto Fidalgo-Herrera, Juan Miangolarra-Page, Maria Carratalá-Tejada
Many researchers have studied the appropriateness of using EMG to study the presence of fatigue under different tasks. One commonly accepted fact is that the mean/median frequency tends to decrease or shift to lower frequencies when the muscle becomes fatigued. It is widely reported in the literature that motor unit recruitment strategies can alter when the muscle becomes fatigued. Some of the possible alterations include: de-recruitment of type II muscle fibers; increases in the recruitment of type I muscle fibers; and increases in motor unit synchronization (Bueno, Lizano, and Montano, 2015; Rodriguez-Falces, Izquierdo, González-Izal, and Place, 2014; Tanina et al., 2017). Although these changes are widely recognized, only the muscle fiber conduction velocity has been identified as a factor influencing changes in the power spectrum of the EMG signals (Koutsos, Cretu, and Georgiou, 2016). Despite the amount of research conducted on the shift from higher to lower frequencies in fatigue, no article could be found pinpointing a set of frequencies particularly responsible for the shift of power toward lower frequencies.
Design considerations for the development of neuromuscular electrical stimulation (NMES) exercise in cancer rehabilitation
Published in Disability and Rehabilitation, 2021
Dominic O’Connor, Olive Lennon, Conor Minogue, Brian Caulfield
Early work established that phase durations of 20–200 µs were sufficient for motor stimulation [61]. However, research into phase duration manipulation during HF-NMES application has demonstrated that higher phase durations may be optimal, leading to greater levels of muscle activation and higher torque output. Indeed, Gorgey et al. [62] measured the activated cross-sectional area of the quadriceps femoris in seven healthy participants and reported a 40% greater level of motor unit recruitment when comparing 150 µs and 450 µs phase durations. Higher motor unit recruitment logically translates to increased muscle force production. In support of this, Hultman et al. [2] demonstrated that increasing phase duration from 150 to 500 µs achieved a 40% greater torque output. In addition, when comparing low (200 µs) and high (500 µs) phase durations, healthy young individuals have been shown to tolerate and generate higher force tetanic muscle contractions (45% v 49% maximum voluntary contraction (MVC)) with a higher phase duration [63]. However, many HF-NMES applications use phase durations of <300 µs [3], despite the evidence supporting the use of higher phase durations for muscle strengthening applications.