Race Day: Why Everything You Know About Training Runs Goes Out the Window (Part 5 of 12)
Race Day: Why Everything You Know About Training Runs Goes Out the Window (Part 5 of 12)
By Ali | AliRunsOnInsulin.com | The Run Starts Before the Run Series
I have run 15 marathons. And I will tell you something that took me an embarrassingly long time to fully accept:
Race day is not a training run with a medal at the end.
It is a completely different physiological event. The crowds, the nerves, the start corral, the adrenaline — all of it changes your blood sugar in ways your training runs never prepared you for. And if you go into race day expecting your numbers to behave the way they did on your long runs, you are going to spend a lot of miles confused and chasing.
This is Part 5 of 12 in my series on running with Type 1 diabetes. Today we’re talking about race day — the unique variables that make it different, and how to build a protocol that actually accounts for what your body is going to do.
The Adrenaline Effect: Your Biggest Race Day Variable
Here’s the thing about race day that nobody puts in a training plan: your nervous system doesn’t know the difference between excitement and stress. Race morning anticipation, the energy of the crowd, the corral shuffle, the gun going off — all of it triggers a release of stress hormones, primarily adrenaline.
Adrenaline tells your liver to release stored glucose into your bloodstream. It simultaneously reduces insulin’s effectiveness at driving that glucose into your cells. The result is a blood sugar spike that has nothing to do with what you ate, what you bolused, or how carefully you followed your protocol.
Research studying competitive T1D athletes found that in the vast majority of races, blood sugar was measurably higher in the two hours before a competitive event compared to an identical non-competitive training session at the same intensity. The difference was purely psychological — the word “race” on the calendar was enough to change the numbers.
One experienced T1D marathoner described the pattern precisely: adrenaline alone spiked blood sugar by 100 points or more in the hour before the start, even after following the exact same plan that had worked perfectly in training. The solution wasn’t more insulin — it was anticipating the spike and not panic-correcting it.
That last part is critical. Over-bolusing to chase a pre-race spike is one of the most common race day mistakes T1D runners make. The adrenaline that drove the spike will dissipate once you start running, the exercise will begin pulling your blood sugar down, and the correction insulin will still be active. The result: a low somewhere between miles 3 and 6 that derails your entire race.
The approach that works: anticipate the spike, accept a higher starting number than you’d prefer, and do not aggressively correct pre-race. Running will bring it down. Your job is to manage it, not eliminate it.
The Corral Problem
Here’s a race day scenario unique to distance running: you arrive, you check your blood sugar, it looks reasonable. Then you stand in the corral for 45 minutes to an hour waiting for your wave to start.
You are not moving. Your basal is still running. Any insulin you took with your pre-race breakfast is still active. And you are about to run 26.2 miles.
This window — the corral wait — is where a lot of T1D runners quietly go low before the race even starts. If your number is drifting down while you’re standing still, you need to eat something right there in the corral. A gel, some chews, glucose tabs — whatever you’re already carrying. Do not wait until the gun goes off to deal with a dropping number.
A small top-up snack 15 to 30 minutes before your wave starts is standard practice for many T1D runners, regardless of where their blood sugar sits. It provides buffer for the wait and for the first mile before your body fully adjusts to race pace.
Race Morning Nutrition: The T1D Version
The general guidance for marathon morning is to eat 2.5 to 3 hours before your start time — enough time to digest without feeling full during the race. For T1D runners, the timing and the bolus require extra thought.
A few principles that matter specifically for race day:
Eat what you’ve practiced. Race day is not the time to try a new breakfast. Whatever pre-long-run meal your body has handled well in training is your race day meal. The familiarity matters — your gut is already dealing with adrenaline-related changes in digestion.
Reduce your breakfast bolus. The combination of the long run ahead, the reduced basal rate you’ve already set (90 minutes before your start, as always), and the adrenaline-driven insulin resistance means your breakfast bolus should be meaningfully lower than a normal day. How much lower depends on your personal patterns — this is where your training log earns its keep.
Account for the wait. If your race has a long walk from parking to the corral, an early bag check, or a crowded start area, you may be on your feet and moving for an hour before the gun. That activity matters. Build it into your planning.
Mid-Race Fueling: More Than a Training Run
For marathon and half marathon distances, expert consensus for T1D athletes recommends consuming 60 to 90 grams of carbohydrates per hour during the race to maximize performance — this is higher than typical training run fueling.
Race pace is typically harder than your long training runs, which means you’re burning fuel faster. Race day also tends to run hotter (sun, crowds, nerves) and longer (real finish lines, not GPS estimates), so you need more in the tank than you think.
Fuel early and consistently — don’t wait until you feel like you need something. By the time your body signals hunger or fatigue at race pace, you’re already behind. Take in carbs at regular intervals from the start, not just when your CGM tells you to.
Your CGM on Race Day: Trust It Differently
Your CGM is your most important piece of race day gear and also your most limited one.
The 12-minute lag we talked about in Part 3 is amplified on race day. At race pace, with elevated adrenaline and stress hormones actively shifting your blood sugar, the gap between what your CGM shows and what’s actually happening in your blood can be wider than usual. A T1D athlete reported their CGM reading before an Ironman showed a reasonable number while a fingerstick revealed a reading that was 140 points higher — the adrenaline and pre-race carbs had hit in a way the CGM hadn’t captured yet.
On race day, carry a fingerstick option if at all possible. Use it when something feels off regardless of what your CGM says. Trust your body over the device when they conflict.
Set your CGM alerts before the race starts — low alarm higher than usual, so you catch a drop early while you still have easy access to your fuel. Once you’re deep in a race, digging into your belt for glucose tabs is harder than it sounds.
The Mental Game Is Different Too
Training runs happen in a controlled environment — your neighborhood, your trails, your usual routes. You know where water is, you know how long you’ll be out, you have your phone and your gear and your routine.
Race day strips most of that away. You’re in an unfamiliar city, on a course you may have only seen on a map, surrounded by 30,000 other people, with medical tents at checkpoints and no guarantee your CGM signal is strong in the crowd.
The anxiety that comes with all of that is real and it directly affects your blood sugar. This is not a mindset problem to be solved — it’s a physiological reality to be planned for.
Two things that help:
First, write your race day protocol down before you go. Blood sugar targets, action thresholds, what you’ll eat and when, what you’ll do if you spike in the corral, what you’ll do if you drop at mile 10. Having decisions pre-made means you don’t have to think clearly under pressure — you just follow the plan.
Second, do a practice race. If your goal is a marathon, run a half marathon first and treat it like race day — full pre-race protocol, race morning nutrition, corral wait, all of it. The first time you experience race day adrenaline shouldn’t be at your goal event.
The Race Day Checklist
The night before:
– Set your CGM adhesive (fresh sensor if needed — don’t race on a sensor that’s ending mid-race)
– Lay out your gear: belt loaded with carbs, ID, phone charged…and take your flat runner photo 😉
– Write your protocol down — targets, thresholds, action plan
– Eat a familiar dinner, nothing new
Race morning:
– Set basal reduction 90 minutes before your planned start (accounting for corral wait and warm-up time)
– Eat your tested breakfast 2.5 to 3 hours before your wave
– Reduce your breakfast bolus from your normal dose
– Bring a top-up snack for the corral
– Do a fingerstick in addition to your CGM check before you enter the corral
– Set CGM alerts before you hand your phone to gear check or tuck it away
In the corral:
– Check your number and trend arrow when you get in
– Eat a small top-up 15 to 30 minutes before your wave goes off regardless of where your number sits
– Do not aggressively correct a pre-race spike — running will bring it down
During the race:
– Fuel early, every mile station, don’t wait for your CGM to tell you to
– Fingerstick if something feels wrong regardless of the CGM reading
– Slow down before you correct — pace change is a safer first response than insulin
The Bottom Line
Race day is its own event. Treat it that way in your planning, your nutrition, your insulin protocol, and your expectations.
Your training runs built the fitness. Your race day protocol manages the rest.
Fifteen marathons in, I still expect my blood sugar to surprise me on race day. The difference now is that I’ve planned for the surprises — and that changes everything.
Always work with your diabetes care team on your personal race day management plan. Individual responses to competition stress vary significantly.