Can you wear a weight vest and hold as heavy a weight in your hands as possible? If the point of Meso 3 is to build strength by doing 8 reps at your heaviest weight possible, there really isn't a substitute for that in Cathe's repertoire. Anything else you are doing is hypertrophy (possibly) or endurance (most likely). Not to say those cannot be challenging and still building strength in your legs, you are just not going to "replace" meso 3 with anything else that is trying to achieve the same goals. I would just do whatever leg workouts you enjoy and find to be non-stressful on your back, while still challenging and that should be fine!
