I’ve written previously about the benefit of seeing real time glucose data through the use of a continuous glucose monitor. Glucose is, of course, the body’s most basic and preferred fuel source.
It’s been a positive learning curve figuring out which off-bike foods and on-bike fuel supports sustained performance over time, distance and varied terrain. Endurance brings an added complexity because you have to balance all of the above with gut comfort, which is no mean feat when you’re talking about fuelling continuous days and nights of full-on racing. That’s a whole lot of processing for a gut folded in half over a bike with blood supply continually diverted to working muscles and skin.
We’ve established Joe’s glucose performance zone (GPZ) over time, the zone where he can push on sustainably and cope with the amount of necessary calories. It’s between 110-139mg/dl. When he’s in this zone he can fuel the effort and when he can fuel his effort you can bet he’s at the sharp end of the race.
We figured out Joe’s GPZ by using the ‘event’ function whereby you measure glucose over training sessions or time periods. You add this objective data to other data fields such as heart rate, power, etc until the glucose pattern emerges. Don’t forget to add subjective ‘feel’ too. Research tells us that pairing objective and subjective data is most useful when it comes to assessing performance.
Race Across the West (RAW) gave us the opportunity to see how valuable all that glucose detective work really was. After all, who cares about data if it doesn’t improve race performance?
I created an ‘event’ for the complete 930 miles, all 68 hours and 53 minutes of it. This event included the 4 hours and 20 mins of off-bike time, which if you followed our race media you’ll know that was mainly due to ‘hot feet’ issues. Joe slept for perhaps 30 mins within those 4 hrs 20 mins.
Joe’s numbers:
He spent 94% of this race in his Glucose Performance Zone with 2% lows and 92 drops. He had zero issues with gut discomfort or hydration status.
Of that 94% in GPZ the majority of time was spent in the 120-129mg/dl with still a considerable amount of time spent between 110-119mg/dl. He sporadically reached into the 130-139mg/dl range.
That’s terrific and dedicated fuelling over 930 miles, 56,000ft climbing, desert heat, sand storms, race load and fatigue. How he did it and what he used, that’s another blog but there’s no magic to it unless consistency is magic…which it is!
2% lows is another terrific data point. A glucose low is a downward trending slope which gets to below 80mg/dl. No athlete wants to be there especially an endurance athlete. You can’t go the distance if your fuel gauge is low and no matter where your blood glucose is coming from (stores such as glycogen, body fat or ingested) low is low.
The 92 drops is the interesting point, that’s nearly 1.5 drops an hour. A drop is a decline of glucose of at least 10mg/dl within a 5-min time frame. These consistent drops might indicate under-fuelling or a period where the fuel, either from stores or ingested, is out of sync with effort.
One data point can tell multiple stories depending on which lens you look through. Joe’s drops, while plentiful, stayed within his GPZ - that’s a strong positive.
However, the drops tell me that his GPZ could and should be more focused on the upper range of 130-139mg/dl. This level of fuelling might sync better with race effort in a more sustainable way thus preventing rapid drops. It also makes sense that performance would be more consistent (baring other factors such as mindset, sleep deprivation, etc) once there is a more stable level of fuel.
This 130-139mg/dl range would require only a slight increase in volume, an extra bite of a bar, extra sips of his maltodextrin based bottle mix per hour or an extra, more complex, top-up feed every 3 hours. You can see how I typically structure Joe’s feeding schedule.
I traditionally err on the side of slight under-fuelling versus over-fuelling. Over-fuelling often leads to gut discomfort as the hours tick by and when nausea, bloating, etc hits mid-race it can take up to 4-8 hours to resolve and by that time depletion has set in, the race has moved on and it’s near impossible to recover. As I’ve said before the gut is the fastest way to a DNF in endurance.
A slight under-fuelling, on the other hand, is easy to fix - you simply eat/drink more - and the effects are immediate. The gut hasn’t been stressed and is more than happy to process those calories.
Looking forward to July 10th, our 7-day Highest Mileage Guinness World record attempt, I’ll be changing a few things based on our Race Across the West data. We’ll be increasing volume and aiming for that 130-139mg/dl zone. I’d expect to see considerably less drops and will be setting short 12 hour ‘events’ during those first few days to assess strategy. Of course, I'll be keeping an eagle eye on gut comfort too.
It’ll be interesting so make sure you follow on all our media channels to get my regular fuel updates. Fuelling an endurance event, particularly the magnitude of the one that’s coming, is nerve-racking. Anything can happen but with my trusty Supersapiens, at least I’ll have data that will help me make good fuelling decisions when it all goes pear shaped and in endurance you can guarantee it will.
Wish me luck!
Interested in performance nutrition coaching? Check me out or drop me a line jill@teamjoebarr.com