IMG 3381

This morning, I decided to get a bit more scientific about my hydration management during my runs this year. The weather at 09:17 was very mild, 70 F. with 76% relative humidity (RH). I ran 4.6 miles in 50 minutes, weighing myself immediately before and after my run. I was surprised that I lost 1.6 pounds of water during this run. I've run regularly in my 20s, 50s, and 60s and sporadically most of my life. I have never carefully measured water loss. 

1.1% body weight loss due to dehydration is still reasonably low. But in marathon training, I've had several brutal experiences in running in August when it felt like the sun was pounding me into the pavement, and I felt like I was staggering rather than running. So, I see this morning's experiment as a wake-up call for the rest of the year.

I did a little research before writing this brief note. A 2% body weight loss due to dehydration can cause a 5% decrease in running performance at the 5 and 10-kilometer distances. A 5% body weight loss can cause a 30% decrease in capacity to work. 

This year, heat acclimatization is a goal. I am not going to avoid the heat but rather selectively train in it to increase my body's ability to deal with it.



Jeukendrup, Asker. n.d. Dehydration and its effects on performance. Human Kinetics.