If you are new to exercising, you may find maintaining an exercise program challenging, particularly if you become sore or fatigued from your workouts. Fatigue is normal, especially at first, and has its benefits. Hitting the point of fatigue will increase your fitness. However, adequate rest between workouts is essential, and moderate exercise intensity will also build your strength, burn calories and prevent injuries.
Muscle Power
Your muscle cells rely on adequate energy, transported within cells by adenosine triphosphate, in order to function. They typically receive ATP through the breakdown of glucose, or sugar, either with or without oxygen. The former process is known as aerobic respiration, while the latter is anaerobic respiration. Anaerobic respiration is a way for your body to produce muscle cell energy even when oxygen stores are low. Your body contains muscles that chiefly use one pathway or the other for their energy supply.
Muscle Fibers
Fast twitch muscle fibers, those used in power movements or sprinting, use anaerobic respiration to use high amounts of ATP for short periods of time. Slow twitch fibers are used for steady output over long periods of time, like distance running, and use less ATP. Fast twitch muscle fibers fatigue more quickly than slow twitch fibers, as anaerobic respiration produces lactic acid, which causes changes in muscle protein formation.
Anaerobic Threshold
When you exercise, your body can use either aerobic or anaerobic respiration as well as a combination. For instance, while you run at a comfortable pace, your body is functioning with both types, but the ratio is low enough that lactic acid is easily removed and your muscles do not reach the point of fatigue. If you speed up, you will eventually reach a point where you cannot remove lactic acid fast enough and your muscles will tire and may even cramp. When this happens, you have reached your anaerobic threshold. By exercising at your anaerobic threshold, you will increase your endurance level.
Moderation and Rest
The best way to prevent fatigue in your muscles is to exercise within your aerobic capacity. One way to discover where your anaerobic threshold is and remain below it is to exercise to the point where your breathing becomes heavy and your muscles begin to burn or tire. Although reaching this point does improve endurance, it will also fatigue your muscles and potentially induce soreness. If you do reach your anaerobic threshold, giving yourself enough time before working those muscle groups again will allow your muscles to recover and repair.
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