Great machine....I train at St. Lawrence Universitys gym (the only gym in my small town) and we have a nice one with an adjustable pad at the back of the ankles.
A few years ago I hurt my back doing heavy hack squats.........the injury got better but was a re-ocurring thing.
I attribute using this machine for re-habbing my back.
At first it was so bad I could barely do it without weight.........worked my way up to 190 for a couple sets of 5 reps.
Not a lot for most guys but my back was bad and I`m not a big guy by any stretch of the imagination.
Just recently hurt my back again doing rack deads......so I`ll be using it a lot more for sure.
If you have access to one,use it.............highly recommended for strengthening the posterior chain.