Mechanisms of muscle weakness and fatigue

Ce texte vise à mettre en place une série d’éléments devant servir de fondement à une interprétation phénoménologique de la pesanteur, à savoir une caractérisation de la pesanteur telle qu’elle se montre et fait sens pour l’individu dans son rapport quotidien, « préréflexif », au monde. Bien que les réflexions ici proposées soient prioritairement à rattacher à la philosophie, nous convoquerons une série d’observations issues des sciences empiriques – au premier chef la psychologie – pour appuyer leur cheminement. Après avoir montré, sur la base d’un ensemble de résultats de la psychologie, que le poids d’un objet manipulé est spontanément évalué/perçu par l’individu sur la base de l’effort requis pour le soulever, et que l’amplitude de l’effort devant être fourni pour développer un niveau de force donné est elle-même proportionnée à la capacité de production de force variable dont dispose l’individu, nous proposerons une première caractérisation phénoménologique de la pesanteur. Nous chercherons à partir de là à mettre en lumière les structures qui, du côté du sujet percevant, rendent possible la manifestation de quelque chose de tel que le poids. Deux idées principales s’imposeront : d’une part, la pesanteur peut être comprise comme une des manières dont l’individu se rend intelligible son monde en référant l’objet qu’il manipule à la prise dont il dispose, au sens de la latitude de son pouvoir d’action ; d’autre part, parce que le poids n’est pas quelque chose que l’on voit mais quelque chose que l’on supporte, quelque chose qui pour être perçu doit être pris en charge, seul un percevant capable de se rapporter à soi comme à une puissance finie, un être en perpétuel épuisement, aura la conformation requise pour rencontrer quelque chose de tel que le poids – pour ouvrir un monde où règne la pesanteur.

This chronic disease, Myasthenia Gravis (MG) is a disease that has no cure, according to some experts.

Myasthenia gravis ( MG) is a neuromuscular disease that leads to fluctuating muscle weakness and fatigue. In the most common cases, muscle weakness is caused by circulating antibodies that block nicotinic acetylcholine receptors at the postsynaptic neuromuscular junction.

However, there are several ways to control and can help in dealing with this chronic disease of Muscle Weakness Disorder.

Learn what is the Relationship between the thymus gland and myasthenia gravis.

Objective. Chronic muscle weakness impacts the majority of individuals after a stroke. The origins of this hemiparesis is multifaceted, and an altered spinal control of the motor unit (MU) pool can lead to muscle weakness. However, the relative contribution of different MU recruitment and discharge organization is not well understood. In this study, we sought to examine these different effects by utilizing a MU simulation with variations set to mimic the changes of MU control in stroke.
Approach. Using a well-established model of the MU pool, this study quantified the changes in force output caused by changes in MU recruitment range and recruitment order, as well as MU firing rate organization at the population level. We additionally expanded the original model to include a fatigue component, which variably decreased the output force with increasing length of contraction. Differences in the force output at both the peak and fatigued time points across different excitation levels were quantified and compared across different sets of MU parameters.
Main results. Across the different simulation parameters, we found that the main driving factor of the reduced force output was due to the compressed range of MU recruitment. Recruitment compression caused a decrease in total force across all excitation levels. Additionally, a compression of the range of MU firing rates also demonstrated a decrease in the force output mainly at the higher excitation levels. Lastly, changes to the recruitment order of MUs appeared to minimally impact the force output.
Significance. We found that altered control of MUs alone, as simulated in this study, can lead to a substantial reduction in muscle force generation in stroke survivors. These findings may provide valuable insight for both clinicians and researchers in prescribing and developing different types of therapies for the rehabilitation and restoration of lost strength after stroke.

The purpose of this work was to examine the intramuscular mechanisms of muscle weakness by quantifying changes in evoked muscle force-time curves following 4-weeks of cast immobilization, and use mathematical models to predict muscle force generation based on the dynamics of Ca 2+ described by a Riccati differential equation. Fourteen young, healthy adults were assigned to either a experimental wrist-hand cast-immobilization group (n=7) or a control group (n=7). Before and after a 4-week intervention period study participants peak evoked force from supramaximal doublet electrical stimulation and the relative rates of evoked force development between 10 and 40% and 50 and 90% of peak force (+dF/dt) were determined along with the relative rate of force relaxation between 90 and 50% of peak force (-dF/dt).