My suggestion is that it is better to write euphemistically and point out your physical problems. Generally, you have your own medical records to prove whether your parents and attending doctors recommend you to participate in military training. Most schools have said that if they really don't adapt to the high-intensity training of military training, after all, students' health comes first. Examples are as follows:
Hello, teacher, I'm XXX (your name) from Class XX, and my major is XX. Due to my own physical reasons (it is best to write down specific diseases here), the amount of exercise in military training is not suitable. I still feel uncomfortable after attending for a few days, and I can't hold on (this sentence can be omitted from the beginning). I have seen a doctor in the hospital before, and the doctor also has the corresponding medical record, so I would like to ask if I can apply for exemption from training, and what is the specific operation of exemption from training?
Secondly, it depends on the requirements of your school, whether it is better to go to the school hospital to open a certificate or to go to an off-campus hospital to open a certificate. If it is a certificate issued by the school, it is still very convenient, just take your own medical record card; If the certificate is issued outside the school, you should also make it clear to the attending doctor what leave you want and why you want to apply for exemption from training. The general practitioner will give you a certificate.