Hydration Basics

I have recently put together a training plan for my nieces who are getting ready for a half marathon run in March, one is a newlywed and her husband has also joined in. What follows here is the answer to some hydration questions that come up. This is a bit different than the discussions I usually have that get deep into technical details.

I hope some other new athletes find this informative, I'll try to make it simple.

Should we be drinking during workouts?

This week was the first long run on the schedule, called for 6.3 miles. So the run was from 50 minutes to a little over an hour. And the first one where water might have been useful. Personally, I have water with me on anything over 20 minutes or so. Do I NEED water for 30 minute runs or rides? probably not, but it's just a habit, and if I get thirsty I have something to drink. In general I say that for workouts over 30 minutes, it would be handy to have some water available. Not that you'll necessarily need it, but if you get thirsty you'll have it.

How much should we be drinking during our runs?

Easy answer, for new athletes who are doing workouts and a run that will take less than 2.25 hours, you should drink enough that you lose between 0 and 2% of your body weight.

Huh?

Well yeah, that's the answer but figuring that out takes a little doing.

How much water do you sweat out?

So the idea is you want to replace much but not all of the water you lose. But how do you figure out how much water you sweat out during a workout?

The training plan I wrote for them already has some long workouts in which the runners weigh themselves with no clothes on before and after the run to see how much weight they lost. For a run in the neighborhood of 1 - 2 hours, you can assume that all the water lost is from sweat. So you simply weigh yourself before the run and after with no clothes on. No clothes because your clothes can actually hold a fair bit of sweat in them. You see what the difference is and you can get an idea if you drank too much, too little, or pretty much right. There's no harm in starting these types of runs immediately.

So if our imaginary niece went out and did her long run starting at 125 pounds and finished at 120 pounds, she netted 5 pounds of water loss. Remember that we want to keep it to 2% of weight loss in the workout. 2% of 125 is 2.5 pounds. She should have kept we weight loss to less than 2.5 pounds. In losing 5 pounds she lost 2.5 pounds too much. 

So next time she runs, assuming the same temperatures, she would need to drink 2.5 more pounds of water than she did today. Remember that's 2.5 MORE pounds, meaning that when you do this during your next run - you need to know how much you drank during the run. It won't help you to know that next time you need drink 2.5 more pounds unless you know how much you drank today.

Luckily for us there's another salient point to know.

1 pint of fluid is roughly 1 pound. So our niece needs to drink 2.5 more points of liquid next time.

Does this change with conditions?

Notice that I said assuming the same temperatures. Different temperatures change the liquid required drastically. A run in 80 degree temperatures will require much more liquid replacement than a run in 45 degree temperatures. Just because you went out last week and found that sweated out 32 ounces per hour - it doesn't mean that it will be the same at the next run if it is much hotter or cooler.

But more importantly, you'll actually be training yourself to have a sense of how much water you need. You'll be getting better at reading your body's cues to how much water you need to get by. So after you have done 4 or 5 of these runs checking your sweat loss, you'll start to have a pretty good sense of how much water you need as you run and be able to read your body's signals.

Can't I just trust my body?

Largely yes, after you have been doing long runs for a while you will probably get a sense of how much water you need. BUT, if you are brand new to endurance training, you might not yet recognize what it feels like when you are a little dehydrated. You might be accustomed to being thirsty in every run and not realize how much of a performance improvement you will get by staying more hydrated during the run. This process of weighing yourself before and after will help educate yourself more quickly and refine your innate sense.

And one other wrinkle. Experiments have shown that athletes naturally drink enough to maximize performance IF THEY HAVE THE OPPORTUNITY TO DO SO. Put a person on a treadmill in a hot environment and have a graduate assistant constantly refilling their water bottles and they will probably drink the proper amount. But who runs with a graduate assistant next to them?

So you have to carry some water with you to give yourself the opportunity to drink. Seems simple in retrospect, but if you take off on a run without enough water to maximize performance - you obviously won't drink enough! 

Does this ever not work?

Actually if your workouts are getting closer to 4 hours than 2 hours then more weight loss is acceptable, it has to do with water being liberated into the bloodstream as you burn your carbohydrate reserves. And a few other things, but as I said these are new half marathon runners so the rules of thumb above will apply.

Is there a way to know if I was dehydrated on a run as compared to anything else?

Actually yes, if you are out there struggling on a run and wondering what is going wrong AND you have a heart rate monitor on. If you are out struggling to hold your normal 8 minute pace and your heart rate is much higher than normal, the first thing you should be suspecting is dehydration. Though if it is much hotter today than your last run it could be simply heat - though heat and dehydration often go together.

On the other hand if you are struggling and your heart rate is much lower than normal then a lack of energy reserves would be your first guess. And that's a discussion for another day.

What do you use to carry water?

There are any number of things to use. I like the ones that strap to your waist. If you search amazon for "2 bottle lumbar pack" you will see several examples starting at about $20. I am writing this in January, so your local discount store like Walmart or Target might have something in stock - they have more exercise stuff around the new year.

Though, I have done many runs with a normal water bottle from the store shoved into the back of the waist band of my shorts, it stays in there pretty well.

I hope this answers some basic hydration questions.