If you're doing long workouts—like marathons or ultra-endurance events—especially in the heat, sipping in 300 to 600 mg of sodium per hour can help your body stay hydrated, keep your blood volume stable, and avoid crashing during the event. But how much you need really depends on how much you sweat and how salty your sweat is.

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.

Taking sodium pills while cycling doesn't seem to make well-trained cyclists faster during a 72 km ride in cool weather — they finish just as quickly with or without it.

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.

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.

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.