I'm all for bodyweight training (you are your own gym, convict conditioning, al kavadlo, naked warrior, barstarzz, coach sommer, calisthenic kings...), and have

I'm all for bodyweight training (you are your own gym, convict conditioning, al kavadlo, naked warrior, barstarzz, coach sommer, calisthenic kings...), and have better results than with metal, without the pain, but this is not it. Seriously, not one exercise for your back, but useless crunches? Do some yoga sun salutation, add some resistance by tensing your body and you have a by far better workout in the same amount of time than this.