A Cyclist’s Insights on cgm data
Since reintroducing myself to endurance athletics in the form of biking 8 years ago I’ve grown to appreciate the nuances of fueling through longer training sessions.
I can clearly remember the first time that fueling “clicked” for me. It was in 2018 on an early spring ride with a friend, Joe, that was 80 miles long and took about 5.5 hours. The prior couple weeks leading up to this 80 mile ride where when things “clicked”. I had been finding that at about 3.5 hours into rides, no matter the tempo of the ride, I’d start to feel lousy and just couldn’t go on with the level of ease I had been enjoying in the first 3 hours.
During this infamous 80 mile “ah-HA” ride, at about the 3 hour mark, I’m sure I said something like, “Woof, I do not feel awesome”, but in the first 2 hours I was feeling awesome. Joe replied, “Dude, have you been eating the whole ride?”. I’m sure I replied with some sheepish response saying, “yeah of course…”. Joe gave some marching orders and I filed in behind him to benefit from drafting and ate a bunch of ride fuel. About an hour later (it takes a while!!!), I was flying again. It was the first time that I can say I absolutely noticed a difference after fueling and bringing myself “out of the hole”.
Have You Been Eating?
Since that ride, I’ve shared a lot of thoughts with a lot of ride partners whom I’m sure have gotten tired of me asking the question, “Have you been eating?”. It has made such a huge difference in building my ability to get in 4-6 hour training sessions with minimal disruptions from a falling off of energy. It truly is amazing how if I’m able to fuel a long ride thoughtfully, there's a huge success rate of those training sessions and ones I’m more cavalier about, those are a mixed bag of outcomes.
How Wearing a CGM Helped Me Gain Insight into Performance
Wearing a continuous glucose monitor for 2 weeks was insightful in that I was actually able to objectively see changes in my blood sugar level during training sessions.
I had some very straightforward endurance rides while wearing the device. An endurance ride is a conversational pace training session and it was great to see that my body was able to keep up with maintaining steady blood sugar over 1.5-2 hour rides without fueling. Doing training rides such as these are valuable as you’re burning fuel your body has on hand (think internal gas tank), and you help drive the body to get better at utilizing and expanding that internal gas tank.
On the other hand, there are the long rides which I mentioned earlier. If someone goes on an endurance ride which is longer than their body is accustomed to, at some point blood sugar will fall off and the rider will experience the dreaded “bonk” which manifests as an utter lack of energy and general awful feelings.
Fueling for a 5 Hour Training Session
I set out on a 5 hour mountain bike ride to thoughtfully observe how my body handles such a training session. In this ride we have 4 trail systems we link up via roads and each trail is roughly an hour in duration. I’m very good at eating on the roads but I’ve always struggled to eat on trail. I’m very much working to improve fueling habits when on trails so monitoring objectively what my blood sugar is doing would be very helpful in understanding cause and effect.
Over the first 1.5 hours of the ride I did a great job of being at 60 grams of carbohydrate an hour, this put my blood glucose at a steady 110-120 mg/dL. At 1.5 hours we entered a trail which I would end up not doing a great job of following the 60 grams of carbohydrate an hour goal. At just before 3 hours in, we were leaving the trail for a road stretch and I had a considerable fall off from how great I was feeling in the first 2 hours. I scanned my blood sugar and sure enough, I had fallen off to 80. Hypoglycemia starts below 60 so I’m at that point not at a critically low level of blood sugar, but as I could tell, it was not a great place to be compared to the 110+ I had been seeing early. I ate a hearty dose of carbohydrates, 60 grams in one go and about 15 minutes later another 40 grams. This was 100 grams of straight sugar which one would suspect to see a big blood sugar spike but I merely maintained and slightly improved my levels to 90-100 for the rest of the ride. When my sugar stabilized above 90, I felt smooth and even, much more like myself and the rest of the training session was a success. At the end of the ride I averaged out to just over my goal of 60g/hour of carbohydrate but as described above, it wasn’t the most perfectly spread out 60g/hour of consumption, but it got the job done.
On a subsequent ride which was just under 4 hours long, on a much less challenging trail, I was able to nail my fueling and I experienced stable blood sugars over the entire 4 hours. I can honestly say, I felt just as good at the end of the training session as I did at the beginning.
How to Plan Fueling
With the Lumberjack 100 looming on June 22nd I can’t say I learned anything “new” with fueling, but being able to objectively see changes in blood glucose levels has given me an even greater appreciation for thoughtful fueling.
If you’re reading any of this and you’re wondering, “how can I start to hone in my fueling strategies?”, my first answer isn’t to get a blood glucose monitor, although they are enjoyable to use as a tool. Instead, plan out your nutrition strategy before your training sessions. Visit a store such as the Rockford Bike Shop and give a look at the various forms of fueling. It can be overwhelming to start, but simply look at the package and see how many servings are in this package, and how many grams of carbohydrates are per serving.
If you’ve never thoughtfully fueled during your training and you’re unsure of what amount to start with, go with 40 grams of carbohydrates per hour and try to get in 20ish in the first 30 minutes, and 20ish in all subsequent half hour blocks. If your belly agrees with that product, great! You’ve found something that works for you. It is becoming increasingly accepted you can train the gut to take in far higher amounts of carbohydrates per hour but if a novice jumps right into 80 grams of carbohydrate an hour, I hope you have some restrooms along your route. It is important to slowly increase the amount of carbohydrates you take in per hour and find your sweet spot of consumption. Once you’re confident you can handle 40g per hour, go with 60g per hour on a later training date.
There isn’t a silver bullet out there as far as products go. Try out hydration mixes which have electrolytes along with carbohydrates. Try out gels. Try out maple syrup packets. Try out stroop waffles. Try it all out!
The biggest goal secondary to completing training sessions for endurance races is learning something from each and every one. If you can have a thoughtful fueling strategy set, and you execute, or fail to execute, that said strategy, you’ll learn something beneficial to take to you next training session. The more training sessions you have results in more insights into your own body. You’ll learn a TON of useful information which is unique to how YOU can set yourself up for successful training and racing.
A note about the author: Dr. Eric Graf is a Chiropractor, Movement Expert, Myofascial Magician, and USA Cycling Certified Coach working on completing his bike fit certification. He trains private cycling clients on performance strategies including fueling, movement, and workout programming.
You can contact him directly to learn more about his coaching style by filling out the form below.
