There are several reasons why a dip in the pool can make you feel sleepy, all of which add up to create the fuzzy, exhausted feeling that comes after a good swim.

1. Physical demand

Swimming may be low impact, but that doesn’t mean it’s low effort. “Swimming engages nearly every muscle in your body, and unlike running or cycling, the water’s resistance increases the effort required,” explains personal trainer Claudia Kwayosa. “This makes it a full-body workout, and after such exertion, your body naturally craves rest.”

All the muscle contractions involved in swimming – especially a high-effort stroke like backstroke or butterfly – can also lead to your muscles becoming fatigued, which is why you might feel both physically and mentally tired after a swim.

2. Water temperature

Even if you’re not going cold water swimming, most pools won’t be as warm as the human body (37°C), so the water will have a cooling effect. This can cause your core temperature to drop, so your body has to work harder to maintain equilibrium.

“Swimming in cooler water can sap your energy as your body works harder to stay warm,” Kwayosa says. “Once you are out, the drop in body temperature can mimic what happens before sleep, making you feel even more tired.”

“Why does swimming make me feel so sleepy?” A personal trainer explains