Gym-goers wishing to develop the major muscle groups of the lower body can do so successfully with the sled hack squat. As with other squat variations, how the athlete places their feet during the exercise has some influence on which muscles receive the most stimulation from the lift.
The quadriceps, hamstrings and glutes will all be targeted with the sled hack squat, but the athlete can shift emphasis onto their glutes and hamstrings by placing their feet further up the platform and taking a wider stance. On the flip side, taking a shoulder width stance with the feet placed lower on the platform will engage the quadriceps to a greater degree.
As the back is fully supported, the sled hack squat is the perfect choice for those with injuries who cannot perform the free weight squat alternatives.
The barbell hack squat is an uncommon sight in gyms, and is widely considered a fairly "old school" exercise. The reason for its demise is likely due to the difficulty in its execution, and there being plenty of other alternative exercises which successfully target the muscles of the lower body.
As with other squatting variations, the quadriceps, hamstrings and glutes are the primary target of the exercise. However, due to having the load behind and below the body (unlike the back and front squat), much greater resistance is placed on the muscles responsible for extension of the hip; the hamstrings and glutes, and less load placed on the knee extensors; the quadriceps.