The method of fitness. Fitness, especially strength training, requires correct methods. If you go to the gym to run and do some aerobic exercise, your goal should be to lose fat. As long as there is enough exercise time, it should be effective, provided that you eat less. If you are doing strength training, your method must be correct, which is not only related to the training effect, but also related to whether you will be injured during training. You can ask a personal trainer to help you.
Careless diet. For people who want to lose weight, it is necessary to control their diet, because the energy you consume in the gym is the energy you took in at the beginning, and the fat that stores energy will not be taken out until it is consumed. For those who want to build muscles, protein is essential after fitness. Because within half an hour after fitness, it is the best time for muscles to absorb protein. At this time, supplementation can quickly gain muscle, or you can eat another meal an hour later.
The time of a single exercise is not long enough, or the interval between groups is too long. Both are important. I won't explain this for the time being. The main problem is the interval. We are used to taking a break for a few seconds after finishing a set of actions, usually 30 to 1 minute. This time actually depends on the kind of exercise you do, but it is probably within this range. This is scientific research and worth carrying out.