Jogging can't be performed forever. As you exercise, the muscles are bound to get worn out from the continuous workload. This fatigue manifests itself as a burning sensation and weakened strength in the muscles. One of the most likely places you'll experience this is in the legs, which perform most of your body's work when jogging.
Cause of Fatigue
Fatigue typically results from the muscles losing their energy to continue performing work. This is traditionally viewed as the process of the muscles failing to receive enough oxygen from the blood to sustain their current workload. But fatigue may also result from the leaking of calcium from the muscle cells that control contractions, according to the New York Times citing research published in the "Proceedings of the National Academy of Sciences" in February 2008. Whatever the exact cause, fatigue is the consequence of performing physical work with your muscles, although other factors -- such as nutrition and physical fitness -- can influence how fast or slow the fatigue develops.
Building Endurance
You can delay the onset of fatigue in your leg muscles by developing endurance through consistent exercise. Aerobic exercise elevates the heart rate and breathing rate to enable your body to get the oxygen it needs. When you become fatigued your body is failing to support the needs of your muscles. Adaptive processes are then undertaken by the body to improve its efficiency when performing this work, resulting in your ability to get better at jogging, extend your distance and pace per run, and ultimately last longer without becoming fatigued.
Handling Fatigue
When fatigue sets in to the legs you are usually safe to continue exercising. Your most important consideration is to make sure the fatigue experienced in the muscles -- the burning sensation -- does not turn to outright pain, which can indicate straining of the muscles. If you are trying to exercise to improve your physical fitness fatigue is something you should push through once it develops -- the development of fatigued muscles during exercise means your body is being pushed to adapt to the stresses of exercise, allowing you to improve as a runner.
Risks
Some fatigue is good for a runner -- it indicates that you are pushing your muscles, getting a good workout and encouraging the development of endurance -- but pushing your muscles to continue working through excessive fatigue could result in injury. Muscles lose their elasticity and strength as they fatigue, making them weaker. If pushed too hard the fibers could become strained or break, resulting in muscle strains that disable the muscle and result in pain and swelling that lasts several days, if not longer.
