If you drink a sports drink with 700 mg of sodium every hour while cycling 72 km in cool weather, your blood volume might go up a little bit because the salt pulls water into your bloodstream from your cells.

Taking 700 mg of sodium every hour during a long bike ride in cool weather doesn’t make well-trained cyclists finish faster — they perform about the same as those taking a fake pill.

If elite cyclists drink as much as they want during a 3-hour ride in cool weather, taking in 700 mg of sodium per hour helps keep their blood fluid levels stable—or even slightly increases them—while skipping it leads to a small drop.

Taking sodium supplements while cycling for 3 hours in cool weather doesn’t stop your blood sodium from dropping slightly — and it’s no different than taking a fake pill. Nobody in either group had dangerously low sodium levels.

Endurance cyclists who take in 700 mg of sodium per hour during a 3-hour ride in cool weather tend to drink about 160 mL more fluid each hour than those who don’t — probably because the salt affects how thirsty they feel.

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.