One good reason to buy and use Super Sapiens, the CGM dedicated to athletes, is to fuel correctly during long sports events. I could not squeeze a long ride in my 14 days using the Abbott Freestyle Libre for the first time : bad weather or on calls impede me from going long on my bike… but thanks to my trusted TacX Neo, I did a long workout indoor. Not as fun, and as « stochastic » as outdoors but still, it’s an experience.
So, one day I just had two fried eggs for breakfast (no carb) and hoped on the trainer for a long workout. My goal was to reach some fatigue I could relate to a decline in energy.
In 2020, I did some long ride in the fasted state and I monitored my estimated energy expenditure (see here or there). What I found is when I « burn » 150ish grams of carb with no intake I start to feel a need for sugar. Above 180-200 g without intake, I have experienced lows. Not really bunking and tunnel vision but definitely less willpower and energy. Some estimations gives me a muscular glycogen reserve of 380 grams. So I suspect when half of it has disappeared, there is a change in my sensations.
Frankly, long endurance workouts on the trainer are quite boring. I pitched up the intensity compared to my usual endurance rides outdoor to burn energy quicker avoiding spending 5 hours riding indoor. I did a 3,5 hours workout with a lot of fatmax intensity, one hour of high zone 2 intensity in the middle and some variations in intensity. My average HR was 128 bpm, Garmin rates the aerobic training effet 3,8. NP is 187W, IF is 0,75ish, energy expenditure more than 2000 kcal with zero intake (but I drank a lot, around 2,5 L, Garmin says sweat might be >2L and I had a correct urine output, weight was 62 kg after the ride, 53 of lean mass, 64,9% hydration state). Estimation of my energy partitioning is 143 g of fat and 261 g of carbs. It’s close to what I could have seen during a 100-120k ride with my friends lasting 4-5 hours.
Like in my outdoor rides, I felt a need for eating something around 150 g of carb burnt but my glycemia was quite stable and power was steady. I saw a slight decline in glycemia during the zone 2 intensity (11:00 to noon), like I have already seen, but the overall feeling was good up to 90% of it. I had two short times lower than 0,7 g/l when I stopped for a minute to get some water and at the stop of the workout.
You see that my 2 eggs around 8:00 are not visible on this graph. Studying the evolution of my glycemia during this long workout, there is no easy pattern I could rely to my feelings. I started feeling low during my zone 2 around 11:30. After noon, I was willing to stop. Mental saturation and low energy surely. Around 200 g of carbs burnt without compensation I really decline fast. The last 30 minutes, in Fatmax zone, were a pain.
Was Super Sapiens useful during this workout ? I feel not. Of course, it’s only one piece of workout and it’s « stupid » to draw quick conclusions, but on this precise workout, I can not see a translation of my sensations on this glycemia graph. I find that having good estimation of your energy expenditure and knowing yourself to manage your energy intake during workouts and race need some work and I have a hard time imagining that Super Sapiens would be THE shortcut to have another way of monitoring the balance between intensity and energy intake. A thing that I still find interesting is using it during a race but it’s not on my schedule any soon :-/
Another way to see this graph is that maybe the slow decay of glycemia during a steady, long effort is the path to bonking ? Then, the manufacturer should develop a way to see the graph on our bike computer or watch with a good visualization of the tendency of the graph with the right scale. Quite a challenge…
I need some rest now. Thank you for reading.