Integrate a substantial calisthenic exercise into your daily routine. Something like a hundred pushups and a dozen pull-ups. Increase the count as you get lighter and stronger so you're always within 10-20% of the maximum you could do in a set. Make it a non-negotiable part of your day akin to brushing your teeth and showering. This way when you fuck up your diet/lifestyle, you have a very strong negative feedback si…
100 pushups?? I can't even do 5 in a row. No upper body strength at all.
This is a maintenance/hygiene routine, the objective is to do this daily until you're dead or otherwise disabled. Just make sure the amount is enough to both have great negative feedback and confer obvious health/fitness/physique advantages you'll be upset about losing.
It doesn't matter if it takes you 10 years to reach 100/day, what matters is that you kept doing it every day up to and beyond that >=100 point in time.