If your goal is to lose fat, then your first task is to lose body fat while retaining muscle. In the process of reducing fat, you can carry out light weight and high repetitive training to help keep the muscle mass unchanged, and at the same time increase aerobic exercise, such as running and swimming.
If your goal is to gain muscle, then you should focus on increasing muscle mass. Moderate and high-intensity strength training, especially focusing on core muscle groups, can stimulate muscle growth. In this process, paying attention to a balanced diet and strengthening nutritional supplements can help muscle cells to better synthesize protein and grow.
Generally speaking, fat loss and muscle gain are not completely independent, so we need to make a customized fitness plan according to our own situation. If you are new to fitness or are not sure about your goals, it is recommended to seek professional fitness guidance.