Since I published my fairly optimistic May 27 2008 post on this topic, I’ve a few observations and thoughts to add.

1. It takes considerable discipline to keep up with my drinking, especially now the hot weather is here. (I don’t like to use the central AC if i don’t need to. I just strip to my shorts when it’s hot.) For a couple of days I attached a 45 min timer to a pint bottle, and that worked, but…

2. It seems to be quite easy in hot weather to wake up dehydrated. I have a pint every time I pee at night but I guess you can evaporate quite a lot during 8 hours in bed. Don’t really want to

3. I’ve had several long rides and it seems quite feasible to maintain hydration. If I drink at least 1.5 oz/mi or 2+ in hot weather then I don’t seem to be dehydrated at the end. I have the impression that the kidneys take a break on their polyuria craze while exercising.

4. I’ve had some very good rides and no really bad ones since I upped the drinking. But there have been several on which it seemed as though I was staring at the end…

If a well rested and prepared cyclist goes out for a ride, she or he can ride very hard for a couple of hours. After that, things slow down and effort level (as monitored by heart rate) diminishes as though approaching a steady state of roughly 65-70% of max heart rate as the limit of what can be sustained. After many hours riding, huffing and puffing up a hill and enduring considerable muscle pain, you can get it a little bit higher than that. But that compares with taking a similar hill at the start of the ride much faster and with ease at 90-95% max HR.

The difference, as I understand it, very roughly, is that at the beginning you have the glycogen reserves available which can be metabolized quickly and anaerobically. At the end you have to rely on metabolizing fat aerobically. Some of your muscle cells are the type that burns glycogen, other fibers burn fat, and some others can do a bit of both. So at the beginning of the ride you can use all your leg muscle as both fuels are available, at the end only the fat burners are working.

Sustainable HR depending on ride durationI figure effort level using heart rate. There’s a lot you can read about on the web about why that’s reasonable. The graph shows my best guess, based on experience, how my sustainable heart rate depends on ride duration, which is on a log time scale from 10 seconds to 100 hours (assuming I’m well warmed up for the short rides).

I’ve had several rides recently when I felt like I was starting at the end of a ride. The heart rate I could sustain at the beginning of the ride was around 145 to 155. There were no other issues. I recently rode, for the fifth time overall, the Boston Brevet Series 300 km in 12:24, 16 minutes faster than my previous best. So I’m riding fairly well but it’s definitely different.

It feels and seems as though I’m starting my rides with depleted glycogen reserve. And I think this may be the case. My suspicion is that lithium produces chronic dehydration which, among other things, cripples the glycogen recovery between rides.