I’m sorry but can you explain to me like I’m a 5 year old… exactly what you put in one of your bottles for a humid hot race? With exact measurement?

What length race? What time duration?

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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For an IM bike… Say 5 hour ride.

Without any considerations for logistics:

5-7.5L water.
5-7.5 tsp Sodium Citrate
2.5 cups sugar
1/3 scoop of Gatorade per bottle (for taste)

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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1tsp of Sodium Citrate has ~1.2g sodium and supposedly absorbs better than salt?

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Dimond Bikes Superfan

Absorbs the same as salt... but less likely to cause osmolarity-based GI distress because fewer total molecules per molecule of sodium delivered.

Here's my "canned" info I've shared a few times here.

Using sodium citrate in place of table salt allows your gut to tolerate more sodium consumption during training. Sodium citrate has 3 sodium molecules for every 1 citrate molecule. Sodium chloride has 1 sodium molecule for every 1 chloride molecule. That means that for the same amount of sodium consumption, there will be a greater number of molecules ingested, if using table salt, rather than sodium citrate. Osmolarity is the number of molecules per unit volume of solution. Our gastrointestinal tracts are sensitive to very high osmolarity solutions. During normal daily living, consumption of very high osmolar solutions (lots of molecules per liter) causes a laxative effect 20-60 minutes after consumption. During exercise, it causes gut cramping, THEN a laxative effect. My personal experience with this can be described as "not fun!"

FYI: Sodium Citrate has about 1000mg sodium per tsp. Table salt is about 2000mg sodium per tsp.
END canned info.

Any error in sodium measurement, even if 10-20% is very unlikely to be make or break for either GI issues, or performance. Hence, I keep numbers very round and eyeball measurements very quickly. Unlike carbohydrate, where if you're 20% high or low on your intake there, there can be very measurable results, either in GI distress or poorer performance via hypoglycemia.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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Got you. I guess I did the math wrong. Duh!....
100 oz. are about 3 liters, which would call for 3,000 mg of sodium, right? 1/2 teaspoon of salt has 1,150 mg of sodium (1 teaspoon has 2,300 mg). So, for 24 oz., I should go for a 720 mg of sodium, which is a little less than 1/3 teaspoon salt?
And if 1,500 mg of sodium is needed per liter use a little more than 1 teaspoon citrate (1,080 mg) for 24 oz.?
When should sodium be increased from 1,000 mg of sodium per liter to 1,500 mg of sodium per liter? What are the parameters?

Calcs look pretty reasonable.

Sodium should be increased from 1000mg/L when you can't offset the sodium losses you think you may be experiencing via sweat loss, any other way. As in, your fluid consumption rate is already maxed and you think you may be able to handle higher concentration of sodium.

If you even notice that you're sweating, you're probably losing >1 L/hr. Goal should be to offset both fluid loss and sodium loss. Never one without the other. Gut tolerance sets your upper bounds for both.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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I found both of these threads to be quite helpful. As a 12hr MOPper I've never bothered to look at the math side of it before, just drank what was on course. Any difference in recommendations for the extreme sweaters or is it still follow the basic math? I manage to dehydrate and cramp up even when grabbing two cups of Gatorade at each water stop during marathons or IMs.

Thanks so much for shedding light on this! This is very helpful!

Fellow extreme sweater here.

Still follow all the math the same. You just have less room for error than fitter, less sweaty, people. You'll need to be right up near gut tolerance for sodium and fluid intake. Whatever that is for you. Remember, gut tolerance reduces with dehydration, so it will change as the race progresses.

For reference, I'll be a 12hr MOPer too, once I do my first 140.6. Target time for Oceanside 70.3: under 6hr is fine. Under 5:30 would be a big success.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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Thank you, that is good info. Not sure how I survived Florida under 12 hours, cramped up at the beginning of the run and started pounding Gatorade and Base Salts. Ate the whole tube of base salts in 5 miles which somehow brought me back to life rather than causing digestive issues. Lucky I guess, sure wasn't good planning.

Still planning to use on course Gatorade, but going to work on getting a lot more of it down earlier and supplementing with sodium as appropriate. Bonking isn't an issue...just those damn dehydration cramps.

Good luck with Oceanside!