Keep the dose very low. There will be a threshold where if you take more than that, you will get androgenic side effects. Voice cracking, hair growth, enlargement, etc. So if you are going to do it, start extremely low and taper up each week. If anything bad happens, go back to lower.
Deva is a burning compound. Women typically use it to put on mass for bodybuilding or whatever. It's not going to be a performance enhancer for the triathlon. If you want to inject, I'd consider primobolan. Promo may give you performance benefits, and it won't have many sides. Or injectable anavar. Or injectable Winstrol. Deca would not be my first (or second or...) choice if I were in your shoes.