Gist
Only modestly compared with free-weight squats. The back support reduces balance and trunk demand, even though some bracing is still required.
The calves support ankle control on the platform, but ordinary hack squats are secondary calf work unless the machine is used for a deliberate calf-raise variation.
Only modestly. The guided path emphasises knee and hip extension, while the hamstrings usually receive less direct tension than in hinges or curls.
Yes. Hack squats are one of the clearest machine-based options for progressively loading the quadriceps through a stable path.
Yes. Deep, progressively loaded hack squats can train the glutes, although machine design and foot placement strongly affect the hip demand.