Iron U is not a medical device and does not give medical advice. It plans training. It does not diagnose anything, treat anything, or tell you whether it is safe for you to train.
See a doctor before you start. A check-up before your first hard session is the first job on the Iron U timeline for a reason: a resting ECG, blood pressure and bloods. Tell the doctor you are training for a 70.3.
Stop and get help if you have chest pain or pressure, faint or nearly faint, become breathless in a new way, or feel your heart beating strangely. Stop that day. Do not wait for the app to say so.
The readiness breaker can be wrong in both directions. It reads sleep, resting heart rate and heart-rate variability from your watch and only ever makes a day easier — it never asks for more. But a watch cannot see a strained calf, a virus coming, or a bad week at work. A green day is not permission. If your body says stop, it beats the watch.
Heart-rate zones are estimates. Yours are worked out from the maximum and resting heart rate you entered, or from your age if you did not enter them. An age estimate can be ten beats out either way. A laboratory test is the real number.
Ask a doctor about pain, illness, injury and medication. The coach in the app will not answer those, on purpose.
Short versions
One line — shown once during onboarding (79 characters):
Iron U plans training. It is not medical advice. See a doctor before you start.
Two lines — Settings → Legal:
Iron U plans training. It is not a medical device and it is not medical advice. See a doctor before you start, and stop if you have chest pain or feel faint.