Training slightly below the point at which your muscles burn, known as the lactate threshold, also enhances your body's capacity to endure high-intensity exercise. This is known as maximum steady-state training. This is the "tempo" run for runners. Begin by jogging at a strong speed for around 20 minutes. Then, without slowing down or speeding up, maintain this running pace and see how long you can stay on the track. The longer you can keep this effort up, the fitter you become. Muscle burns are very real things; they're the result of lactic acid building up in your bloodstream. As this acid builds up, you start to feel pain in your muscles and skin. If you stop moving, the acid will build up to such a level that it will cause serious health problems. That's why it's important to rest when you feel any discomfort during exercise. You should be able to continue even after you feel sore, because muscle strength decreases as we age. However, if the pain gets too severe or you cannot continue, then you should seek medical help immediately.