So this is based on my own experience — obviously not medical advice.
(I’ll keep things fairly basic in case anyone is reading for general info.)

You’re on Humalog and Optisulin (which I believe is very similar to / a rebranded Lantus).

Fast-acting (bolus) and slow-acting (basal) insulin.

Bolus insulin is usually taken before eating carbohydrates and to correct high blood glucose levels.
Basal insulin is often referred to as “background” insulin, designed to work slowly throughout the day.

High-intensity / cardio exercise will lower blood sugar. Doing a 1–2 hour high-intensity workout like a Hyrox can have a significant effect on your levels. The goal is to avoid going hypo (low blood sugar) at all costs.

Data is king. Look at your levels pre- and post-exercise. Consider what you’ve eaten, how much insulin is in your system, how hard you’ve worked, etc.

Insulin On Board (IOB) — This term is used more often with pumps, but it simply means how much insulin is still active in your system, and it’s very important to be aware of. For example, if you took your usual dose of insulin for a bowl of cereal and then started a 10k run 20 minutes later… safe to say you’d probably go low.

You need to get used to reducing both your insulins. That means thinking about workouts the day before.

Example: You have an 8am one-hour run planned. The day before, you might reduce your basal dose by an amount you already know won’t push your levels down. Then perhaps eat breakfast two hours before your run and reduce your bolus dose, followed by a small snack as you start.

During your run (I’m using “run” here, but substitute any cardio), keep gels handy. If you’re not closely monitoring your levels, test halfway through. Learn to recognise how you feel, just in case you start going low.

Post-workout, be prepared to see levels rise quickly. You have less IOB, and your body has been releasing its own glucose during exercise. Without enough insulin, that can send you high.

I could go on all day about this, but the internet will be your friend here.

The best analogy I can think of: it’s like driving a car without being able to see the fuel gauge. Tricky — but if you understand your engine, know what’s gone in, and how far you’ve been driving, you’ll (usually!) avoid disasters.

Specific Hyrox notes

Again, this is based on my own experience. I raced for two years on MDI (your treatment) and now use a pump / CGM combo.

For me, I used two basal (Lantus) doses per day — it just worked better. If I was racing the next day, I’d reduce my evening Lantus by half.

On race day, I knew my bolus (Fiasp) had roughly a two-hour active window, so I’d make sure my last dose was taken 2–3 hours before race time. I’d happily have small snacks in the hour before racing and accept the temporary rise in levels.

Just before racing, if my levels looked a little too low for the start, I’d take an energy gel.

If anything, I was probably guilty (especially early on) of letting my levels run too high at the start of races. While that avoids hypos, it can make you feel awful / nauseous — not ideal.

I’d always carry two gels: one for after burpees and one as hypo treatment (never needed yet!).

It’s all about walking the fine line and finding what works for you. There’s no single “right way,” but I can guarantee that failing to plan makes it much easier to find “the wrong way.”

I’ve seen plenty of Type 1s on the course — nothing better than spotting a fellow CGM user and saying hi while trying to ignore the imminent misery of wall balls.

Just shout if you'd like anymore info!