By Mark Enstone, Coach
We want to remain properly hydrated. Always. As humans but especially as athletes. One rule of thumb is to pee clear-ish (neither like apple juice, nor like water, but like lemonade). While that is always a good measure, we can get a little more precise than that (you don't have to, but you can):
Hydration is important at any time of the year, but is perhaps more important during our hot summers, especially when the humidity is also high. For those of you wanting/interested in a little more insight into your level of hydration and what a run does to it, weigh yourself before and again after your run/workout (minimally with shoes-off but also as near naked as you can socially acceptably be (ideally, you don't want to weigh a sweat-soaked shirt after the run, so shouldn't weigh it dry before the run).
A question we sometimes get is (some flavor of): "Whoa! I lost 5 pounds, is that 'normal'"? Normal, common, but non-optimal. Sweat rates differ from person to person. No, there is nothing strange about how much weight you lost, nothing abnormal, but you do want to try to not lose quite that much. Why? We want to avoid dehydration. Dehydration increases the risk of early fatigue. For races, that might mean a slower race pace or even a DNF (did not finish), or simply a less enjoyable race. For training runs, it means that that final mile up Waller Street will seem longer and less pleasant than it should! Not feeling dehydrated doesn't mean we aren't becoming dehydrated, it's a question of degrees.
For your runs leaving from Rogue EQ, there is a scale in the training room. For your runs leaving from home, use your own scale at home. For your runs where you, for example, drive to Barton Springs Pool, park there and run from there, take your own scales from home with you in the trunk of your car.
Get into the habit of weighing yourself pre and post run. The more often you repeat it, in different conditions -- heat, humidity, effort level, etc. -- the more you'll zero in on understanding your fluid intake requirements. Repeat the pre and post-run weighing exercise constantly (no, not all the time, but here and there in different temps, humidity, conditions, effort level, etc.). It takes but ten seconds! If you get in a habit of doing pre and post-run weigh-ins, you'll "get a feel" for what you should/could be consuming on your runs in different conditions. My guess is that you'd be surprised at how much you need to be drinking. Over time, your post-run number will get closer to your pre-run number automagically.
Your goal is to weigh the same after the run as you weighed before the run. Any weight loss is, of course, lost water. Sweat. Plus electrolytes in that sweat. It is also possible to drink too much fluid. So we also don't want to overhydrate, drink too much. That can lead to other problems, the first symptom of which might be a "water sloshing" sound in your stomach. Therefore, we want to weigh fairly close to same pre- and post-run.
What if your pre- and post-run weigh-in numbers differ? In our summer weather, I'm guessing that the post-run number is smaller. Kudos if it is the same. And you might, might have a post-run number that is larger, you gained weight. In winter weather, we may more easily balance our hydration, or even over hydrate. If the numbers differ, you didn't quite get your hydration quite right for this run (for this distance, at this temperature, at this humidity, at this effort level). As a quick yardstick, 16oz of water weighs 1lb; one of those "cone cups" is 4oz (filled to the brim). So, for example, if you lost 3lbs during a run, you should/could have drunk 48oz more of fluid, 12 cone cups. If you gained 2lb, you should/could have drunk 32oz less of fluid, 8 cone cups.
Billy Mays: "But wait, there's more."
Actually, we can tolerate some level of dehydration. Up to 2%. By "tolerate" I mean that the adverse affects of dehydration, the increased fatigue, might not arise until we're 2% dehydrated. This allows us some "wiggle room" if we simply can't consume the extra, say, 48oz of water that a maintain-hydration approach requires. 2%? A 2% dehydration affects your athletic performance. But a 1.9% doesn't? Hmmm. Personally, I try and stay clear of even getting near 2%. A weight loss of 3-5lbs probably puts athletes less than 150lbs over that "affects performance" 2% threshold.
The human body can't store excess water. Instead, we constantly operate in a state between fully hydrated and some level of dehydrated. Prehydrating the day(s) before ideally put you at the fully hydrated state, you probably re-hydrated when you woke before your long run, and tried to stay ahead of the game during your run ... and that's where you came up short.
We don't actually need to (necessarily) balance fluid intake with fluid loss during the run. Some net loss is OK, and possibly unavoidable in our summer temps/humidity. We need to prevent getting "too" dehydrated, and we can use the "2%" threshold as a guideline. We'd need to replace the imbalance after the run.
This gets a little more complicated, but let's take some numbers as an example, and dive into some detail. Let's first assume we want to remain in balance.
You lost 3lbs during a 90 minute run. To replace all of the fluid that you lost, that would mean drinking an extra 48oz over that 90 mins in addition to what you actually drank. That's an extra 16oz per 30 mins, an extra 4 full cone cups per 30 mins, an extra 2 full cone cups per water stop? Do-able? Maybe that's a lot of water? Let's look at whether, and how to avoid, that "2%" threshold. Did you get close to that threshold? Let's say 2% of your pre-long run (normal, well hydrated) weight is 2.5lbs. Same 90 mins run. So, yes, you stepped over the 2% threshold. To prevent hitting your 2% level, you only want to lose up to about 2.5lbs, no more (less is ideal, but we've drawn the line in the sand at 2%). So, you really want to address the "excessive" loss. The 0.5lbs of loss (I.e. 3-2.5) 0.5 lbs is 8oz. So you would have needed just 2 extra cups (8oz) during the course of your long run today in those conditions. Do-able? Certainly.
Sweat is water+salts/electrolytes and replacing it with just water means we're diluting/losing electrolytes. And those are important for all sorts of things inside our body to keep you operating safely.
Arguably, maintaining hydration is more important for race performance, but every run we do is an opportunity to practice. Then, come race day, whatever the weather/temp/humidity, you'll have the information to fine tune your race hydration plan. Finishing your training runs and workouts suitably hydrated will also aid in your recovery in addition to making them more enjoyable.