Mechanisms of muscle fatigue in intense exercisehttp://www.tandfonline.com/doi/abs/10.1 ... 4197367254
The manifestations of fatigue, as observed by reductions in the ability to produce a given force or power, are readily apparent soon after the initiation of intense activity. Moreover, following the activity, a sustained weakness may persist for days or even weeks. The mechanisms responsible for the impairment in performance are various, given the severe strain imposed on the multiple organ systems, tissues and cells by the activity. At the level of the muscle cell, ATP utilization is dramatically accelerated in an attempt to satisfy the energy requirements of the major processes involved in excitation and contraction, namely sarcolemmal Na+/K+ exchange, sarcoplasmic reticulum Ca²+ sequestration and actomyosin cycling. In an attempt to maintain ATP levels, high-energy phosphate transfer, glycolysis and oxidative phosphorylation are recruited. With intense activity, ATP production rates are unable to match ATP utilization rates, and reductions in ATP occur accompanied by accumulation of a range of metabolic by-products such as hydrogen ions, inorganic phosphate, AMP, ADP and IMP. Selective by-products are believed to disturb Na+/K+ balance, Ca²+ cycling and actomyosin interaction, resulting in fatigue. Cessation of the activity and normalization of cellular energy potential results in a rapid recovery of force. This type of fatigue is often referred to as metabolic. Repeated bouts of high-intensity activity can also result in depletion of the intracellular substrate, glycogen. Since glycogen is the fundamental fuel used to sustain both glycolysis and oxidative phosphorylation, fatigue is readily apparent as cellular resources are exhausted. Intense activity can also result in non-metabolic fatigue and weakness as a consequence of disruption in internal structures, mediated by the high force levels. This type of impairment is most conspicuous following eccentric muscle activity; it is characterized by myofibrillar disorientation and damage to the cytoskeletal framework in the absence of any metabolic disturbance. The specific mechanisms by which the high force levels promote muscle damage and the degree to which the damage can be exacerbated by the metabolic effects of the exercise remain uncertain. Given the intense nature of the activity and the need for extensive, high-frequency recruitment of muscle fibres and motor units in a range of synergistic muscles, there is limited opportunity for compensatory strategies to enable performance to be sustained. Increased fatigue resistance would appear to depend on carefully planned programmes designed to adapt the excitation and contraction processes, the cytoskeleton and the metabolic systems, not only to tolerate but also to minimize the changes in the intracellular environment that are caused by the intense activity.
you need adequate magnesium for ATP transport. ATP is the body's 'energy currency'. there's a great Khan Academy online lecture about it. the resulting disturbed calcium cycling could be linked to your feeling weak. magnesium also happens to be suboptimal in ms patients. and as for the possibility of disturbed potassium-sodium balance when ATP is depleted, that could tie in to some other symptoms you've mentioned elsewhere:
Sports Nutrition Basics
Part 6 - Fluid Replacement & Hydrationhttp://www.sport-fitness-advisor.com/sp ... fluid.html
Sodium concentration in the blood can reduce due to sweating and drinking lots of diluted fluids. If it gets too low it can lead to nausea, headaches and blurred vision
. Adding just a pinch of salt can offset this potential danger.
Sodium is also an electrolyte. Electrolytes help control the passage of water between body compartments and they also help to maintain the acid-base balance of the body. Electrolytes (or lack of them) have been associated with muscle cramps in the latter stages of sport games.
normally i would say that ms patients need to stay as active as possible, while ensuring that nutrient levels are optimal. if someone had the poor nutritional status common to ms patients and then depleted their status further through intense exercise, i would think that would speed progression.
if you rest and ensure suspect nutrient levels are replete, your body should be able to get over it. have your doctors run any tests re possible ms?