Hi,

No need to rush. I know there is pressure on everyone to look good but you're only 14, you've got at least 7+ years of growing to do. (btw women go for more than a 6-pack )

5x a week for HIIT I would say is far too much especially on a day when you're training legs!

Try two days on two off to begin with. I 'may' do boxing on the same day as HIIT. It depends on your training aims. If it is just to get fit then do them on the same day. If you want to improve your skill level in boxing I could look to stay fresh.

If it were me, I would prefer to do something like HIIT with as little as possible in my stomach. One choice would be to have a small glass of juice to give you a boost of sugar and then have something balanced after. Cottage cheese is low fat and a good source of prot. It's also cheap.