The first group performed one set of free squats for 8 - 12 reps to failure, while the second group performed multiple sets of lower reps but not to failure. (fitnessandpower.com)
For best results, do free squats instead of hack squats. (fitnessandpower.com)
The belt squat takes a lot of effort to set up, but I think it is the only machine - free squat version that places no weight on the spine. (scoobysworkshop.com)