Just make a bet with a friend. Work out 4 days a week, for each day missed you owe him $100, same for him. Proof must be provided at the end of the month (most gyms allow you to get a list of your check-ins)
That's kind of what you're doing if you get an expensive gym subscription and don't go.
No it’s a different psychological trigger.
I pay the same amount for my gym membership whether I go or not. What GP is asking for would only cost money on the days they don't go.