Monday, October 16, 2006
Biking with Dex
One of my major motivations for purchasing a DexCom was to help me improve my BG management during my training for and racing of Ironman Couer d'Alene. I've been able to use it on a few bike rides now, and a couple of runs. I am withholding final judgement on its performance at this time; although I can say I have experienced both enthusiasm and disappointment.
This past weekend, I had a wonderful ride in the Bay Area, starting near Woodside, CA, riding up and over Skyline, down to the Pacific Ocean, and back up and over and down again, back to Woodside. The ride starts out with about 15 miles of rolling, mild grades, followed by about 4-5 miles of a moderately steep climb (Old La Honda for those who know the area). Once up on Skyline, the descent is long and fast and fabulous (maybe about 15 miles)! We kept up a pretty high cadence during the descent along 84W. After a quick ride along Highway 1-North, we started back up the mountain through Tunitas Creek--a very steep 3-mile climb followed by another 3 miles of climbing a more moderate pitch. Down we went on King's Mountain Road and then wound our way a few miles through Woodside and back to the start along Canada Road. The total distance was about 52 miles.
I'm including a graph showing the DexCom values and my BG values during the ride. I ate a banana around 8 AM and took about half of my regular dose. Later, after noticing that my BG's were rising more than I was happy with, I took my full dose. We started riding around 9:20 AM. Unfortunately, the software doesn't have any other graphing options for the time axis, but somewhere around 10 AM I noticed that my BG was falling, much more than represented by the DexCom. I ate a Luna bar + 1 GU and didn't take any insulin. You can see the large peak from this snack. I am so worried about dropping low when I exercise that I often end up having some hyperglycemia. I didn't take any insulin for the rest of the ride, but did eat another Luna bar and a couple more GU's at some point. We finished riding sometime around 1:30 PM.
What I might do next time is eat just the Luna bar or the GU and then eat again in another 40 minutes. I've learned that I do often overreact to falling BG's and that it doesn't always take a huge intake of carbohydrates to correct it. I have had an experience in a race where I ate several GU's, a PowerBar and a bag of Skittles and still had a hard time keeping my BG in a decent range. But this was probably due to eating too little earlier on, given the intensity of my ride. I think that, as long as I haven't had a huge insulin bolus recently, I can probably keep my BG's stable on an ride with carb intake every 30-60 minutes, depending on the intensity of the ride.