The details of a hot, long run…

not a view from my run, but hot nevertheless

Most runners simply drink when they are thirsty. While this works for shorter workouts, not knowing some hydration basics will cause you to crash during longer training runs.

Last Sunday, I needed to a long run and didn’t roll out of bed in time to beat the heat. It was around 88 degrees when I started at 1:00pm and didn’t arrive back home until 4:00pm. Thinking about the time of day and length of run, this is probably the worst idea for a long run. I would not recommend this tactic but I was curious to see just how my body reacts to heat. Note: I was well hydrated and had periodic water stops on the trail.

First off, here are some hydration basics:

  • Water needs vary from person to person. A smaller runner may sweat one pound per hour while a bigger runner can sweat four pounds. To put pounds of sweat into perspective; one pound equals 16oz. So the bigger runner is sweating a half gallon every hour!
  • There are many ways to make sure you’re hydrated but the simplest is by the color of your urine. Clear is good, dark yellow is bad. The best way to hydrate is drink water well in advance of your workout. Start drinking about four hours before and stop with one hour to go. This will give the kidneys time to process and rid any excess.
  • Super-hydrating right before a run will not work. The body can only process about 20oz of water per hour. So downing a big Gatorade right before a long run will only leave you bloated and dehydrated. Most likely you’ll have to make pit stops at mile 3 and 5.
  • Most runners who lose more than 2% of their body weight due to sweating will have to slow down and most likely have to walk. For me, a 170 lb person, this is 3.4 pounds of sweat loss.
  • Sweat is not just water. Sweat also contains electrolytes. Electrolytes are sodium, potassium, calcium, and magnesium. Drinking a sports drink with electrolytes is a good idea to replace those essentials particles. For my run, I just drank water. Ideally, drinking Gatorade or Powerade would be better as they contain electrolytes.

During my long run, I started off well hydrated. Although I have not measured my sweat rate, I would guess it’s around 2.5 pounds per hour or 40 ounces. My water stops were further apart than I would have like, about 40 minutes. Due to the large gaps in water intake, I drank as much as I could without bloating.

Two hours into the run, my sweat total was around 5 pounds/ 80oz and my water intake about 40 oz. The amounts are estimates since I didn’t weigh myself and was drinking out of water fountains. In total, my net sweat loss after two hours was 40oz or just under 2 pounds.

If you remember that 2% loss of body weight from sweating can cause you to significantly slow down, and I was close. My body weight is 170, so 2% would be 3.4 pounds or 54oz.

At the end of my run, my sweat total was around 7.5 pounds/ 120oz and my water intake about 55oz. My net sweat loss for the run was 65oz. Considering 54oz causes a significant slow down I should have been feeling pretty crappy…and I was. My attitude turned from positive to negative, I wasn’t smiling at other runners and cursing bikers under my breath for not getting over on the trail. The music turned from motivating to annoying. Thinking back on it now, the 2% loss of body weight really did indicate dehydration. This was approximately the moment I turned from finishing strong to crashing and just trying to finish.

Overall, it was good to find out how well I do in heat, but next time, I think rolling out of bed earlier would be wiser.