Traditional thinking that we don't want too much sodium is becoming outdated. The current thinking is how to match sodium intake to sodium loss. The only exception might be people on medication for high blood pressure.
While "sweat rates" can vary widely from athlete to athlete, let's use a general rule of thumb: you will lose 1L of sweat per hour in warm and/or indoor conditions. In that 1L of sweat, you lose between 1000mg to 3000mg of sodium!
It even surprised me how much this was per hour when you consider most electrolyte drinks are only providing 300mg to 450mg per bottle.
I've been monitoring my training for the past few weeks and carefully trying to replace the exact amount of fluid and salt I'm using per hour.
The results have been more impressive than I expected. My performance has been remarkably consistent, and my next-day recovery is better than expected.
One of the most surprising things I noticed is that I was far less thirsty at night. This meant I didn't need to hydrate at night and, as a result, had a longer stretch of uninterrupted sleep.
I would consider myself a "salty sweater" and I estimated I was in the '2g of sodium loss per 1L' of sweat. Most of my workouts were 60 to 90 minutes, and I would use two 22oz Feed Bottles per hour.
The two bottles provided me ~1.5 L of fluid replacement, pretty close to what I was losing in 90 minutes. But then, to get 3g of sodium over the two bottles was much harder than expected.
The best solution I found was the LMNT Hydration at 1g of sodium per bottle. It is undoubtedly a bit salty tasting, but they do an excellent job with their fruity flavors in covering this up. The extra salt also made me want to keep drinking, so getting through the two bottles was no problem.
If you prefer a very light flavor to your drink, you can also try Tailwind Nutrition Endurance Fuel - Naked Flavor. My tip is to use 2-3 scoops per bottle, giving you 303mg of sodium per scoop.
Most of us won't wholly replace everything we lost during our workout, and this is where post-workout hydration is ideal. I'll either refill one of my 22oz bottles or use a 32oz Purist Bottle if it is handy.
I recommend you sip this "rehydration" bottle over the next 2 hours. You have a few more options here for rehydration drink mix to use.
Consider these two options for rehydration for extreme situations when it is sweltering and you have been going for more than two hours.
1) The Right Stuff at 1780 mg of sodium
2) Skratch Hyper Hydration at a whopping 1720mg of sodium