Effect of dehydration

I noticed on my last three runs that my pace has not been improving, but has slowed in fact by almost 2% over the past week, over the same distance. This is a bit disappointing, as until this week my pace has generally been improving on every run. At first I wondered if I could be overtraining. Even though my total weekly mileage is currently pretty minimal, it has been growing by about 12-13% per week, which is quite a quick rate of increase, and above the 10% that most coaches recommend. I am reluctant to change my training plan though, as I do have a 10K race to prepare for, and I need to get up to running 10K fairly comfortably before the end of September.

Another possibility I thought of was that I might be slightly dehydrated. According to this article, a reduction of only 1% in the body's water content below the optimum level may lead to a slowing in running pace of around 2%, due to factors like decreasing muscle endurance, decreased cardiac output and decreased skin cooling. If so, this alone could explain the recent drop in performance.

The article goes on to explain that the average daily amount of water consumed by someone of my weight is around 3 litres. I reckon my own consumption is quite a bit below this, even if I include other fluids like tea and coffee. So from today I am going to try to always drink this amount every day.

Apparently, I should drink additional water before and during exercise, at a rate of about 100ml for every 10 minutes of exercise. So for my typical 20 minutes or so of running, I should drink around 200ml of water. It hardly seems worth carrying a bottle with me for such a short run, so I think I will try the 'water loading' approach, which is to load up on about 500ml of water approximately 30 minutes before running, so that it has left the stomach and begun to enter the bloodstream before the run starts. I will try this tonight and see if my pace starts to improve again.

Once my runs get longer than about 50 minutes, I will start carrying a water bottle as well, so as to be able to continue the 100ml per 10 minutes rule once the water load has been used up.