(Although this would potentially lead to a completely subsidized transport system... but then you could increase the barrier to getting the free ticket or have the barrier depend on the person's physical fitness... and you might get the cost for the tickets back from the decrease in healthcare costs... it's just got so much potential!)
What if you started giving free tickets to people who can do 60 sit-ups, or 100, instead of 30? Wouldn't this mean free tickets for men only (or mostly)?
As for the men-only part... enhance the system to not use a fixed number but have that number depend on the applicant's estimated gender, age, weight etc.
You could even gamify this, gain money from selling people's user statistics (ugh!) etc.
Don't let diversity scare you away from doing things - do them, but make best efforts to be inclusive.
Why would you think that? Body weight exercises are generally easier for smaller built people to get good at. For one, it gets harder and harder to add more muscle as you get bigger, and secondly smaller built people have shorter distances to move. If it was limited by explosive strength, maybe, because it's harder for women to grow large muscle volume, but if you can do 10-20 plus, it's pretty much down to endurance beyond that point.
That's speaking for Germany, at least. Sadly, I can imagine what such a lawsuit would look like in the US rather well :(
By `mostly work', I mean `good enough for an art project'.