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Organomercurial Compounds
Published in Fina P. Kaloyanova, Mostafa A. El Batawi, Human Toxicology of Pesticides, 2019
Fina P. Kaloyanova, Mostafa A. El Batawi
Since early symptoms of intoxication with methylmercury are similar to those of polyneuropathy, electrophysiological methods investigate the peripheral nervous system for an early diagnosis, von Burg and Rustan24 applied these methods in an investigation on 14 subjects, 5 months after being exposed to methylmercury; in the culmination of exposure, these subjects had had from 1000 to 3000 ng/cm3 mercury in blood. At the moment of the investigation, mercury content in blood was 100 to 800 ng/cm3. According to the authors, the clinical electrophysiological indices did not support the thesis that methylmercury intoxications produce effects similar to peripheral polyneuropathy. The methods of investigation they applied could not reveal any consistent identical disturbances in the different subjects affected. The only interesting data were those of the decreased threshold of “H” reflex. Some authors are of the opinion that the damage of the specific inhibitory centers in the low section of the brain stem could explain the easy stimulation of “H” reflexes.
Muscle energetics and electromyography
Published in Kumar Shrawan, Mital Anil, Electromyography in Ergonomics, 2017
Results on α motor neuron excitability indicated that there was very little change, if any, in the maximum amplitude of the H-waves for the control leg while the experimental leg post-H-wave was markedly reduced by static stretching. The mean relative reduction in the H/M ratio from pre- to post-test for the control and experimental legs were 0.63 (p>0.05) and 21.5% (p < 0.01), respectively (see Figure 5.13). These results are entirely consistent with earlier studies (deVries 1961a, b) and further suggest that the inverse myotatic reflex which originates in the Golgi tendon organs (GTO) may be the basis for the relief of DOMS by static stretching. Since the H-reflex involves tonic MUs (Mcllwain and Hayes, 1977), it is likely that the lb afferent inhibitory effects from the GTO could be mediated through the tonic MUs, thus reducing the evoked H-wave amplitude.
Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Examples of spinal reflexes are: the flexion reflex that moves a limb away from a harmful stimulus, the stretch reflex in response to muscle stretch, and the tendon-organ reflex in response to muscle force. Examples of reflexes elicited by stimulation are the H-reflex and the tonic vibration reflex.
Influence of hysteresis on soleus Hoffmann reflex during plantar flexor muscles stretching: a pilot study
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
M. Datoussaid, S. Baudry, N. Guissard
Muscle-tendon complex acts as a viscoelastic material (Taylor et al. 1990) that implies a decrease in passive torque during unloading compared with loading conditions, a phenomenon called hysteresis. Hysteresis of the muscle-tendon complex is manifest during a passive stretching maneuver as a lesser passive torque when relaxing the muscle (unloading phase) after stretching it (loading phase; Guissard et al. 1988). Hysteresis is assumed to take place in muscle rather than tendinous tissues (Kubo 2018). Meanwhile, the spinal neural loop that conveys information from muscle spindles is depressed, as indicated by the decrease in the amplitude of the Hoffmann (H) reflex, in soleus during and immediately after muscle stretching of plantar flexor muscles (Guissard et al. 1988). This suggests a decrease in the net excitatory input of group I afferents onto spinal motor neurons due to inhibitory mechanisms. However, the impact of hysteresis on H-reflex amplitude remains unknown. One could assume that a decrease in passive torque during the unloading phase may reduce inhibitory processes acting on H-reflex circuit. Such a result would suggest that part of the inhibitory mechanisms acting on H-reflex circuit is related to passive tension. The aim of the study was to compare the H-reflex amplitude in soleus during the loading and unloading phases of a stretching procedure of the plantar flexor muscles.
Neural mechanisms of strength increase after one-week motor imagery training
Published in European Journal of Sport Science, 2018
Sidney Grosprêtre, Thomas Jacquet, Florent Lebon, Charalambos Papaxanthis, Alain Martin
However, when tested during MVC, the superimposed H-reflex (Hsup/Msup) remained unchanged. In fact, this differs with actual training, showing an effect on both resting and active spinal excitabilities (Holtermann et al., 2007). This result indicates that MI did not involve a global arousal of spinal circuitry but has impacted specific circuits. Indeed, while Hsup involves both pre- and post-synaptic mechanisms, Hmax changes are more likely attributed to presynaptic mechanisms, acting at the level of Ia afferent-to-alpha-motoneuron synapse, and to the excitability of the motoneurons itself. Although a direct change in alpha-motoneuronal excitability after training cannot be totally ruled out, MI was recently shown to result in a sub-threshold cortical motor output that could modulate the activity of spinal structures that mediates presynaptic inhibition of Ia terminal onto alpha-motoneurons (Grosprêtre et al., 2016). It is known from animal experiments that such structures are more sensitive to weak stimuli in comparison to alpha-motoneurons (Daniele & MacDermott, 2009). It can be suggested that the Hmax increase after MI training might be the result of a reduction of spinal presynaptic inhibition rather than a direct impact on alpha-motoneuronal output, although this assumption deserves further experiments to be confirmed.
Manipulation of sensory input can improve stretching outcomes
Published in European Journal of Sport Science, 2018
Robyn A. Capobianco, Awad M. Almuklass, Roger M. Enoka
The significant increase in range of motion observed after self-massage may be due to modulation of neural pathways. For example, Behm et al. (2013) evaluated the responsiveness of spinal reflex pathways and twitch contractile properties after massage at the musculotendinous junction of the soleus, tapotement massage (using percussive strokes) of the triceps surae, both massage techniques with stretching, and a control condition. The amplitude of the Hoffmann (H) reflex decreased after all three conditions, but the effect was greatest for the tapotement plus stretch condition. The decrease in H-reflex amplitude was evident immediately after the intervention and up to 2 min later. Twitch contractile properties, including peak torque, time to peak torque, half relaxation time, and electromechanical delay did not change across conditions. Similarly, Goldberg, Sullivan, and Seaborne (1992) found a greater depression of H-reflex amplitude with 3 min of deep massage of the triceps surae compared with light massage of the same duration. It is possible that the self-massage technique used in the current study had a similar effect, and the reduced responsiveness of spinal reflex pathways allowed for a greater range of motion.