Ever get tired after a strenuous workout at home or the gym? Or, ever have your muscles ache after a few hours of working in the yard or some other physical tasks? When human muscle fatigues, athletic performance becomes impaired, according to RoutledgeSport.com. For those individuals suffering muscle or metabolic diseases the effects of muscle fatigue can make everyday tasks difficult. Understanding the scientific processes responsible for skeletal muscle fatigue is therefore central to the study of the physiology of sport, exercise and health. Muscle fatigue occurs when the muscles cannot exert normal force, or when more effort than normal is required to achieve a desired level of force, according to WiseGeek.com. There are a number of causes for muscle fatigue, ranging from exercise-induced fatigue to genetic conditions which lead to muscle weakness. Muscle fatigue is recognized as a physical issue which can be very dangerous for patients.
According to the Sports Medicine topic on About.com, everyone who exercises realizes that you can’t exercise at a high intensity for long before your muscles tire. You may also know that how long you go depends upon how hard you go. So what causes fatigue and why does it occur faster when you exercise harder? The reason has to do with several factor including the availability of energy to fuel muscle contractions and the mechanism of calcium in muscle cell action.
First, let's consider the energy pathways the body uses for exercise at different intensities, according to About.com. During intense exercise, such as sprinting or lifting heavy weights, muscles rely on anaerobic metabolism, which can only produce a certain amount of energy at a time, unlike the aerobic metabolism system, which can produce energy over hours. Muscles use something called ATP (adenosine triphosphate) as an energy source. ATP is created in essentially two ways. One is by aerobic metabolism using oxygen carried in the bloodstream. This is a sure and steady way to create virtually unlimited sources of energy; however, it has a limit on how fast it can work. The cardiovascular system is limited in its ability to quickly deliver blood and oxygen to the working muscles. Because of this, during high intensity exercise, ATP is also provided by anaerobic metabolism that don't require an ongoing supply of oxygen. Anaerobic pathways can provide ATP immediately, but they also have limited stores that need to be refilled after they are used up. Training can make a difference in how long and fast both of the metabolic pathways work. Trained athletes have a greater ability to quickly deliver oxygen to the working muscles which increases the ability to use aerobic metabolism at a higher exercise intensity. Trained athletes also develop a greater efficiency in both energy deliver, and skill. Finally training may improve the way the body creates and uses the anaerobic systems so you can access ATP more readily.
A recent study by Columbia University Medical Center found that muscle fatigue experienced by athletes after long and intense exercise may be caused by a problem with calcium flow inside muscle cells. fatigue occurs due to tiny leaks of calcium inside the muscles. One of the functions of calcium is to help control muscle contractions. This research found that after extended high-intensity exercise, small channels in the muscle cells begin to leak calcium, which leads to weakened muscle contractions. This leaked calcium also stimulates an enzyme that attacks muscle fibers and also leads to fatigue, noted by Proceedings of the National Academy of Sciences.
In the case of exercise-induced fatigue, according to WiseGeek.com, muscle fatigue is believed to occur when the body temporarily exhausts its supply of energy. Some studies have also implicated disruptions in the flow of calcium through the muscles. Exercise-induced fatigue is usually not treated as a serious medical problem, because it will resolve after rest, and people can train their bodies to get more endurance so that they will not fatigue as quickly. Muscle fatigue is also directly related to the type of exercise someone engages in, and athletes often vary their routines and the intensity of their workouts for this very reason. When physical exertion is not the obvious cause of muscle fatigue, or when minimal exertion results in severe fatigue, it can become a cause for concern. Weakening muscles are an issue not only because they contribute to a decline in quality of life, but because muscle weakness can eventually lead to heart problems and breathing problems, and some chronic conditions like Lou Gehrig's Disease, also known as ALS, actually cause death via muscle weakness, as the patient becomes slowly paralyzed and stops breathing. Processes in several areas of the body can contribute to muscle fatigue, including issues with muscles and nerve cells at the site of an area of fatigue, along with problems with the central and peripheral nervous system. When a patient presents with chronic muscle fatigue, a doctor may use a number of tests, including stress tests, to uncover the cause of the muscle fatigue and to learn more about it. The doctor may also look for related symptoms like joint pain, tremors, and so forth. A number of genetic and acquired conditions can lead to muscle fatigue. The treatments for these conditions vary, depending on the patient and the disease. These treatments can vary from the use of medications to manage or eliminate the condition causing the muscle weakness, to physical therapy which is designed to strengthen and condition the patient's muscles so that he or she will be more functional.
For the professional or amateur athlete, there's no thrill like reaching the finish line. And, according to StreetDirectory.com, there's nothing more frustrating than not reaching the finish because of the debilitating effects of muscle fatigue. It's long been understood that dehydration and carbohydrate depletion are the main causes of exercise-induced fatigue. Athletes know they can prolong their activity by loading up on carbohydrates and drinking plenty of fluids. However, recent studies also reveal there are additional key factors that contribute to fatigue during prolonged exercise:
1.) Dehydration: During exercise, the body loses water through sweating and evaporation. Sweat is the way your body keeps from overheating as sweat glands release perspiration that evaporates, cooling the skin and the blood underneath. The cooled blood then flows back to cool the body's core. Even mild dehydration can impair athletic performance. To restore the body's fluids that are lost during exercise, athletes should consume beverages that contain agents such as glucose and sodium, two ingredients found in most sports or energy drinks. These agents help maintain blood volume and aid in the absorption of water into the body.
2.) Overheating: During exercise, an athlete's body temperature, typically about 98.6 degrees, can increase to temps up to 104 degrees or more, especially during intense exercise. While a certain percentage of blood is used to regulate body temperature, large quantities of blood are still required to meet the energy and metabolic needs of working muscles. These demands can overtax the circulatory system, resulting in inadequate removal of body heat and a rise in an athlete's body temperature. Research has proven that athletes involved in endurance sports can experience risks of overheating. Studies indicated that athletes who drank fluids during a two-hour run lowered their body temps by two degrees compared to those who did not rehydrate.
3.) Depletion of Muscle Fuels: During intense short-term exercise, fatigue can result from depletion of glycogen. Glucose is the predominant fuel source for muscles in the first 10 seconds to three minutes of intense exercise. During long-term exercise, the aerobic pathway kicks in for energy production. In addition to glucose, fatty acids and amino acids are burned as fuel for aerobic metabolism, providing a wider range of energy resources. However, glycogen depletion contributes to muscle fatigue even during long-term exercise. During studies, when athletes exercised to near exhaustion at 80 percent of their maximum capacity, the glycogen content of their muscles dropped to near zero in about 90 minutes. Through carbohydrate loading, endurance was increased and glycogen storage capacity was enhanced. These results suggest glycogen is a crucial fuel for energy production. To preserve glycogen, some athletes adopt the method of training the muscles to become more efficient in using fat as a fuel source by completing several extended training sessions, each lasting more than two hours. This method stimulates the enzymes responsible for the conversion of fat into energy, which enables athletes to burn a higher percentage of fat and conserve glycogen for more strenuous efforts.
4.) Low Blood Glucose: In addition to providing energy for muscles, glucose is also a source of energy for the brain and nervous system. In fact, 50 to 60 percent of the glucose supplied by the liver is used strictly for brain and nervous system function. During longer exercise sessions, glycogen stores run low. This reliance on muscle glycogen is balanced by an increased reliance on blood glucose for fuel. After two to three hours of exercise, the majority of carbohydrate energy appears to be derived from glucose, which is transported from circulating blood into exercising muscles. This causes blood glucose to decline to relatively low levels. Fatigue occurs because there is not enough blood glucose available to compensate for the depleted muscle glycogen. The use of sports drinks, carbohydrate gels and sports bars help athletes keep good blood glucose levels elevated to maintain central nervous system function and provides carbohydrates to working muscles. Studies show that athletes are capable of absorbing up to 80 grams of carbohydrates per hour during exercise, delaying fatigue by as much as 30 to 60 minutes.
According to eHow.com, when people work out and feel a sensation that thier muscles are tired, aching, or exhausted, or get to the point that they are working out so hard that they feel as though they can not move thier muscles for another minute, they're experiencing muscle fatigue which limits the performance of the muscles and gives the muscles a sensation of exhaustion. Muscle fatigue can be delayed through diet, hydration, recovery and supplements. Drinking beverages that contain electrolytes and carbohydrates such as Gatorade and Powerade, help the body replace those that are lost during exercise. Caffeine can also help delay muscle fatigue because it causes free-fatty acids to release into the bloodstream, which helps the body burn fat and generate energy. Staying hydrated is essential, and a person who drinks 10 to 12 glasses of water every day can delay muscle fatigue substantially. Maintaining a healthy diet and including an adequate amount of carbohydrates, fat and protein in a diet is extremely helpful in warding off muscle fatigue, according to Realsolutionsmag.com. Athletes should make 40 to 60 percent of their diets carbs and about 30 to 35 percent of thier diets should be protein, since these help the body produce energy according to Realsolutions.com. When the body has adequate amounts of these, it helps it sustain energy and hence delay muscle fatigue.
Before you start your exercise regimen, or plan to spend several hours doing strenuous labor, make sure you follow proper safety precautions for your health to prevent significant muscle fatigue. Follow proper diet guidelines, and keep well hydrated. Short term fixes may help delay muscle fatigue, but usually the long term effects can cause physical damage if not corrected. Everyone at some point suffers from a certain degree of muscle fatigue. Taking care of yourself when you experience it is the best way to maintain a healthy lifestyle.
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