Now I do 100 push-ups every day (half an hour) to exercise my muscles, and I feel nothing the next day. Is this really useful?
It's really useless to do this, because it's the taboo of fitness, that is, the muscles in the same part can't practice for two days in a row, because there is not enough rest time for the muscles, and the muscle strength has no time to grow at all, so it seems that it's a waste of effort to practice hard.