Spinning is an aerobic exercise, which has a good effect on losing weight and fat. You were tired at first, because your physical strength couldn't keep up. I suggest you run for a while, but not too much, because you are thin, so you should practice your physical fitness first. There are still some skills in cycling, and you need to cooperate. If you want to practice muscles, don't mainly ride bicycles, but mainly practice equipment. Some large muscle groups should be practiced more, and squats should be effective when they are cool, and aerobic exercise should be put behind. Don't lose muscles because of your long-term aerobic exercise.