Probably because swimming uses a lot of muscles and you aren't used to using those muscles.
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Swimming is a good workout to work almost all the muscles in your body at once. It mostly uses your arms and leg muscles. It also tones your core mucles a lot.
For all these sports the muscles of the legs are needed.
Yes, it improves your strength and helps your muscles. By swimming a lot, you can also lose a lot of weight.
your abdominal muscles, your bingo wings (your upper arms) thighs, possible calve muscles
Swimming is a good workout to work almost all the muscles in your body at once. It mostly uses your arms and leg muscles. It also tones your core mucles a lot.
You use many things. You use equipment and muscles.
synchronised swimming. it's swimming and smiling and there's four of you.
none
every muscle
Swimming