So, every time one of our muscles is continually stimulated, as with intense exercise or weight lifting exercises, the force or tension that is able to be developed by the muscle fibers itself becomes diminished. This resultant failure of muscle fiber to be able to maintain a contraction as a result of contractile activity is known as muscle fatigue.
This onset of post workout and during workout fatigue depends on both the type of skeletal muscle fibers as well as the intensity and duration of the muscle contractions. With heavy weight lifting or with intense exercise, the white muscle fibers, also called "fast twitch" fibers, appear to rely more upon anaerobic metabolism. These fibers fatigue more rapidly, and are used more for short duration, high intensity activities. The development of muscle fatigue corresponds to four events that occur in working muscles:
1. The depletion of the amount of available ATP. In this scenerio, the rate of ATP utilization exceeds the rate of production. The muscle cannot contract without ATP. Therefore, the muscle fatigues. 2. An increased in the levels lactic acid. Lactic acid is a bi-product of anaerobic metabolism, which is the type of metabolism used most frequently during weight training or exercise programs with goals of improvimg muscle strength. 3. The depletion of muscle glycogen levels. As the amount of available glycogen diminishes, the muscle can no longer sustain a contraction. 4. Levels of other metabolic waste products increase within muscle cells. If levels of acid and carbon dioxide waste products build up, this will slow aerobic metabolism, resulting in less efficient metabolism.
If muscle fatigue sets in and the muscle is no longer able to sustain the exercise or activity, the muscle becomes overloaded resulting in micro trauma to the muscle fibers. If this fatigue and overloading is repetitive or long term in nature the resulting microtrauma becomes cumulative and pathology or injury occurs. Local muscle fatigue is suspect to contribute to injury and diminished performance. In order to avoid the adverse effects of muscle fatigue, a sufficient supply or flow of blood and proper nutrition to the working muscles is critical.
Since aerobic metabolism generates almost 20 times as much ATP for energy as does anaerobic energy, the effects of muscle fatigue can be minimized by ensuring exercise intensity is low enough so that adequate oxygenation, or blood flow to the active working muscles is achieved.
Advanced sports nutrition and supplementation is highly recommended for both anaerobic and aerobic forms of training and exercise regimes. The supplements enhance blood flow distribution to working muscles, hence diminishing the build up of lactic acid and other harmful waste products, while at the same time optimizing proper nutrition. Both factors are critical to optimal exercise performance.