I feel this pain too. When I first went to ID I was in very good shape. I have been athletic for my whole life and it is a part of who I am. But I found myself slipping in ID school. The best way to combat it I found was bike commuting this allowed me to get a workout before and after my time at school. This carried on to professional life also, but as of late I have moved to another place and it is impossible to bike commute. I also had a little one recently and that has also upset the balance in the best way. So my time is very short for myself. There are a few things I do.
-Wake up early go to bed late. This maximize your time. I have never really needed much sleep so this works for me. I am usually up at 6 go to bed 10:30 0r 11.
-Also I go to the gym now (hate it.) But it helps. Usually in the morning before work I like it alright but really like being outside.
-Try to work athletics in on the weekend. I do longer actives on the weekend to help me stay sane. Early wake up around 5:30 and do something till 10:30. That way I get my balance with the family on the weekend.
This is pretty much how I handle it. It’s not prefect for everyone but works for me.