If it is an exercise aimed at strengthening heart and lung function, you should swim for a long time, just like long-distance running. It belongs to aerobic exercise, so you should swim at a speed that you don't feel tired. As for swimming, if you only know breaststroke now, it doesn't matter, just swim breaststroke. Not bad if you know all four tricks. You can swim alternately, which is boring. Every time it should be more than 40 minutes, blood sugar is consumed 40 minutes ago, and fat is consumed 40 minutes later. Of course, if you don't swim for a long time and then start exercising, you should do it step by step and don't pursue it for a long time. As for how long the subject asks, it depends on personal speed. In short, make plans according to your own situation. In addition, you can swim for a long time, interspersed with some speed training, and swim back and forth at your fastest speed to improve your strength. What other fitness exercises are you going to do? Besides swimming, I also run to strengthen my legs. Of course, I can also do aerobics and ride a bike. I used to dance Duoyan Zheng with my wife. Recently, I have been exercising according to the prisoner's fitness instructions. Are there any other precautions? It is also important to simply stretch and relax after swimming, pay attention to the combination of work and rest, and rest and recovery. Don't exercise too much and cause joint pain like me. Keep warm in winter. Don't go swimming if you have a cold. In a word, safety comes first. Don't make yourself too tired when you come up, cultivate interest and establish habits first. After swimming like this for a period of time, you can learn other strokes if you want. Let's answer so much first. That's all I can think of at present I hope it helps. Please correct me if I am wrong.