There is nothing like a vigorous exercise session to make you feel like you've done something positive for yourself. The muscle fatigue and twitching that occur post-workout are byproducts of mechanical work, and indicate that you have challenged your muscles in a way that will cause them to adapt and grow stronger. The fatigue and twitching are likely caused by depletion of fuel, dehydration and depletion of electrolytes, stimulation of motor neurons, damage to muscle fibers. In some cases, statin drugs taken for high cholesterol can be the cause.
Fuel Depletion and Muscle Fatigue
During a vigorous workout, you rely heavily on glucose, a fuel stored in your muscle tissue in the form of glycogen. In order for your muscles to continually contract, they must manufacture ATP, or adenosine triphosphate, which is the primary chemical substance of cellular energy production. ATP production requires a continual supply of glucose, fat and oxygen. The longer you exercise, the more your glycogen stores become depleted, leading to muscle fatigue and weakness. A high carbohydrate post-exercise snack will help you replenish your muscle glycogen,and relieve muscle weakness. Try a bowl of cereal with sliced bananas, or chocolate milk with a sandwich.
Dehydration and Muscle Twitching
Exercise can leave you dehydrated, and that can spell trouble for your muscles, which are made up of large amounts of water. Along with water loss, you may also lose electrolytes, mineral compounds that you need in order for your nervous system to function properly. Calcium, magnesium, potassium and sodium are all essential electrolytes that can be lost through perspiration. A consequence of dehydration and electrolyte depletion is muscle cramping and twitching. Be sure to drink plenty of water before, during and after exercise, and consider an electrolyte replacement beverage like Gatorade or other sports drinks, to restore optimal levels.
Muscle Fiber Damage and Inflammation
One of the results of challenging exercise is minor tearing of muscle tissue that can lead to soreness, inflammation and weakness for several days after a workout. This condition is called DOMS, or delayed onset muscle soreness. The breakdown of fiber is one of the stimuli that promote increased muscle size and strength. The resultant inflammation may cause pressure on motor neurons, the nerves that stimulate muscle contraction, causing the muscle fibers to twitch. The weakness and twitching from DOMS often goes away within three to five days.
Statins and Muscle Weakness
Statin drugs are often prescribed to treat high cholesterol, but they can adversely affect muscle tissue. Symptoms of statin induced myopathy include fatigue, muscle pain, muscle tenderness, muscle weakness, nocturnal cramping, and tendon pain. If you exercise regularly, speak to your health care provider about side effects before agreeing to take statin drugs. If you have just begun an exercise program and are already taking statins, look for side effects of muscle pain and weakness, and discuss any concerns with your health care provider.