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The Mechanics of Gait
Published in Verna Wright, Eric L. Radin, Mechanics of Human Joints, 2020
With weight totally on the limb, stability is gained by extension of the knee and hip. During the early part of midstance the vector is still posterior to the knee and ankle. Therefore, dynamic mechanisms are needed. To allow knee extension, the rate of tibial advancement is slowed by action of the soleus muscle, assisted by the gastrocnemius. Quadriceps activity draws the femur forward. This action indirectly extends the hip, allowing the hip extensor muscles to relax. As the advancing vector becomes anterior to the knee, the quadriceps relaxes as well. Critical to this process is sufficient soleus muscle action to resist the anteriorly aligned vector that is inducing passive dorsiflexion. A contracture of the plantar flexors, which stabilizes the ankle at neutral, is a useful substitute.
Work Capacity, Stress, Fatigue, and Recovery
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
Discomfort is a subjective experience that can result from a combination of physiological and psychological processes including muscle fatigue. Muscle fatigue is a physiological phenomenon that can be observed directly using techniques such as electromyography (EMG). Muscle cells are arranged in functional units known as motor units. Each motor unit is connected to a single nerve fiber and all of the cells in that unit fire in response to an impulse from the fiber on an on–off basis. The number of muscle cells per motor unit varies considerably between muscles—calf (soleus) muscle motor units contain many hundreds of muscle cells, whereas motor units in the eye muscles contain as few as five. The latter muscles are capable of much finer, coordinated movement due to their superior innervation.
Muscle energetics and electromyography
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
Undoubtedly there is a close link between energy metabolism and excitation processes. Figure 5.3 summarizes possible metabolic and electrophysiologic consequences of muscular activity which might lead to fatigue based upon current studies. Prolongation and reduction in the evoked action potential have been reported during high-frequency nerve stimulation (Jones et al., 1979, Moritani et al., 1985a) or during ischémie contractions (Duchateau and Hainault, 1985), indicating a possible dependency on energy supply for membrane function or removal of metabolites and ions. Edwards and Wiles (1981) have shown that patients who are unable to utilize glycogen because of phosphorylase deficiency manifest a rapid decline in the surface-recorded evoked action potential amplitude and the failure of recovery during local ischemia following stimulated contractions at 20 Hz, which in normal subjects recovers rapidly. Furthermore, the depletion of extracellular Na+ has been shown to accelerate the rate of force fatigue in an isolated curarized preparation (Jones et al., 1979). This reduction of extracellular [Na + ] or accumulation of K+ may reduce the muscle membrane excitability sufficiently during high-frequency tetani to account for the excessive loss of force (Jones et al., 1979; Moritani et al., 1985a). In addition, Moritani et al. (1985a) have also demonstrated that the recording of intramuscular-evoked potentials showed the predominantly ‘fast-twitch’ gastrocnemius muscle to have greater reductions in the potential amplitude and conduction time as compared to those of the ‘slow-twitch’ soleus muscle. Thus, energy metabolism clearly plays an important role influencing neural excitation and electrolyte balance within the cell.
Is high soleus muscle activity during the stance phase of the running cycle a potential risk factor for the development of medial tibial stress syndrome? A prospective study
Published in Journal of Sports Sciences, 2020
Aynollah Naderi, Maarten H. Moen, Hans Degens
The dynamic foot pronation during running was a significant predictor for the incidence of MTSS. In line with our study, Becker et al. (2018) have shown that athletes with MTSS have more pronounced foot pronation during running, while static foot posture was not associated with MTSS. Therefore, it appears that dynamic foot posture is a more important predictor of the risk of MTSS than static foot posture. It is possible that increased dynamic foot pronation increases the strain on the tibia through greater peak soleus muscle activity. This may develop into overuse and MTSS if the increased strain exceeds the tibia bone structural capacity. It may be speculated that runners benefit from control of dynamic foot pronation using arch-support foot orthoses and thereby reduce the strain on the tibia. In line with this, a previous study suggested that clinical benefits of arch-support foot orthoses are related to altered magnitude, location and temporal pattern of ground reaction forces during gait (Dowling et al., 2014), but this requires further investigation.
Muscle force characteristics of male and female collegiate cross-country runners during overground running
Published in Journal of Sports Sciences, 2020
C. Nathan Vannatta, Thomas G. Almonroeder, Thomas W. Kernozek, Stacey Meardon
Male runners in our study demonstrated relatively higher gastrocnemius and soleus muscle forces compared to the female runners, which would likely result in greater Achilles tendon loading for the male runners since it is responsible for transmitting gastrocnemius and soleus forces to the calcaneus (Doral et al., 2010). Excessive/repetitive loading without adequate recovery may degrade the Achilles tendon which could lead to injury (Kader, Saxena, Movin, & Maffulli, 2002). As a result, our findings may help to explain why male runners are more likely to develop Achilles tendinopathy (Taunton et al., 2002). We are not aware of another study comparing gastrocnemius/soleus muscle forces in male and female runners. However, our results appear to be consistent with a previous study which estimated Achilles tendon forces using the net ankle plantarflexion moment and the Achilles tendon moment arm and reported that male runners demonstrated greater Achilles tendon loading compared to female runners (Greenhalgh & Sinclair, 2014).
Relationship between pre-exercise muscle stiffness and muscle damage induced by eccentric exercise
Published in European Journal of Sport Science, 2019
Jingfei Xu, Siu Ngor Fu, Dong Zhou, Chen Huang, François Hug
Elastography can be used to estimate the shear modulus of a localized muscle region (Bercoff, Tanter, & Fink, 2004; Bouillard, Hug, Guevel, & Nordez, 2012; Lacourpaille et al., 2014). The shear modulus measured using ultrasound shear wave elastography is strongly linearly related to the Young’s modulus (Eby et al., 2013). Using this technique, an increase in passive stiffness was observed after an eccentric exercise (Guilhem et al., 2016; Lacourpaille, Hug, Bouillard, Hogrel, & Nordez, 2012). The magnitude of this increased stiffness depended on muscle length, i.e. longer the muscle, larger the increase. Using magnetic resonance elastography, Green, Sinkus, Gandevia, Herbert, and Bilston (2012) observed a muscle-dependent change in stiffness after a bout of eccentric exercise. Specially, an increased stiffness was observed in the biarticular gastrocnemius muscle but not in the monoarticular soleus muscle. A recent study from Maeo et al. (2018) also reported a significant increase in muscle stiffness in the biarticular rectus femoris (RF) muscle but not in the two monoarticular vastus medialis (VM) and lateralis (VL) muscles during single-joint eccentric contraction of the knee extensors.