Swimming first, then running is more scientific and good for your body. Running opens up the pores and it takes a while for them to recover. When you swim, all the pores close naturally when your body gets cold. After running, you need to rest for a long time before swimming. Short intervals cause the pores to close abruptly can allow bacteria to remain in the pores, making it easy for skin infections to occur. Muscle pain and leg cramps sometimes occur after running, and if you go swimming after running, there is a chance of drowning and other accidents. Combining the above factors, it is more scientific and safer to swim first and then run.