Why do boxers try to stay celibate during training?

Sex weakens the leg muscles.

https://expertboxing.com/the-real-reason-why-no-sex-before-a-fight

(not certain- read above article- satguru)

Well, I found this information on National Geographic's website and it says that although athletes have believed that sex before an important event decreases their energy and makes muscles weak, it has been proven that sex doesn't actually do so and that it actually increases testosterone levels which make men more aggressive and helps to ease muscle pain.

The site says that coaches just say that athletes should abstain from sex so they will get enough sleep and not have any psychological issues the day of the event.

https://www.nationalgeographic.com/culture/article/news-sex-sports-abstain-athletes