Your muscles contract, and your muscles adapt to rest (or the state when you don't exercise), but when you exercise, your muscles change. You can call it transition or fatigue, because fast walking mainly uses the muscles of heel, forefoot (everyone has different habits) and calf, so it may be sour at first, but after a long time, your muscles adapt to your exercise state. I still have to add that it is normal to feel acid swelling. If it hurts, try to walk slowly, because sometimes walking habits are wrong, and then go back to walking quickly. If it still hurts or can't stand it, your body is warning you. )

The above is about why you are sour and the source of acid.

How to prove whether exercise is effective or not is still measured by a soft ruler. If the calf is thinner, this is effective, indicating that your muscle density is tighter, which is a good thing. Walking is a persistent thing. I wish you perseverance. This is not a sore twice, which means that exercise is effective. The final effect of exercise is to change muscle density.

Regarding the effect, if you are just starting to walk fast, no one can guarantee that it will be effective once or twice. Acid may represent the adaptation period.

Hope to adopt