If endurance-trained guys eat less salt for 9 days, their blood sodium drops — even if they drink enough water — especially when they bike in the heat. This suggests long-term salt intake might affect how their body handles hydration in hot weather.

If fit guys eat a low-salt diet for 9 days, their bodies heat up more and their hearts beat faster when they bike in the heat — even if they drink the same amount of fluids — suggesting their bodies aren’t cooling as well.

If fit guys bike hard in the heat and drink a lot, a sports drink with more sodium keeps their blood sodium steady, but one with less sodium causes it to drop a bit on average.

If fit guys cut down on salt for 9 days, they pee out less sodium—even when exercising in the heat—showing their bodies are adjusting and they’re sticking to the low-salt plan.

Taking sodium supplements during a long bike ride in cool weather doesn’t really change your body’s sodium levels if you're already drinking fluids whenever you feel like it.

If endurance athletes drink a lot during long workouts and also take in sodium, it might help prevent low blood salt levels — but it probably won’t make them perform better just by itself.