Hack squat (machine)
The machine hack squat lets you squat deep on a fixed track with your back supported, which makes it easy to push the quads close to failure. It works in programs that build the thighs, but no trial has tested it on its own, so the grade rests on machine-versus-free-weight data and squat-depth trials.
What the science says
- Builds the thighs in a varied machine program Moderate evidence
Kassiano et al. (2025) had young women rotate 45° leg press, hack squat and Smith squat across the week for 10 weeks; thigh muscle thickness rose 7.5–19.3%, the same as doing the leg press every session. The hack squat was never isolated.
- Machines grow muscle as well as free weights Moderate evidence
Haugen et al.'s 2023 meta-analysis found no hypertrophy difference between machine and free-weight training, with strength gains specific to the modality trained.
- Depth matters, as with any squat Moderate evidence
Bloomquist et al. (2013) showed deep squats grew the front thigh more than shallow ones; the hack squat makes deep knee flexion easy to reach. Extrapolated from barbell squats, not tested on the machine.
How to do it
Muscles trained: quadriceps, glutes, adductors
- Back and shoulders flat against the pads, feet shoulder-width
- A lower foot position puts more work on the quads; higher, on the glutes
- Descend under control to full depth, knees tracking over the toes
- Keep the hips on the pad; do not let the pelvis curl under at the bottom
- Drive up without locking the knees hard
How to apply it
Treat it as a quad-focused squat: go deep, control the descent and take sets close to failure.
Who should be careful
The supported back makes the hack squat a good option for people whose lower back limits barbell squats, but deep knee flexion under heavy load can irritate sensitive knees. Use the machine's safety catches. Anyone with knee or back pain should get individual advice from a physician or physical therapist.
Frequently asked questions
Is the hack squat as good as the barbell squat?
For muscle size it should be. Haugen et al.'s meta-analysis found machines and free weights build muscle equally, though no trial has compared the hack squat directly.
Is there research on the hack squat itself?
Very little. Kassiano et al. included it in a rotating machine program that grew the thighs, but it was not studied on its own.
How deep should I go?
As deep as you can control. Deep squats grew more muscle than shallow ones in Bloomquist et al.'s trial.
Scientific references
- Muscle Hypertrophy and Strength Adaptations to Systematically Varying Resistance Exercises
- Effect of free-weight vs. machine-based strength training on maximal strength, hypertrophy and jump performance - a systematic review and meta-analysis
- Effect of range of motion in heavy load squatting on muscle and tendon adaptations
More exercises
- Bulgarian split squat Moderate evidence
The Bulgarian (rear-foot-elevated) split squat trains one leg at a time and builds the quads and glutes with far less load on the bar than a back squat.
- Romanian deadlift Moderate evidence
The Romanian deadlift is a hip hinge that loads the hamstrings and glutes at long muscle lengths, and trials of stiff-leg deadlifts and similar hip-extension exercises show real hamstring growth, mainly in the semimembranosus and biceps femoris long head.
- Conventional deadlift Moderate evidence
The conventional deadlift trains the whole posterior chain and grip and is a core strength lift, but research on its growth effects is thin: trials either use other deadlift variants or measure strength rather than muscle size.
- Barbell hip thrust Moderate evidence
The barbell hip thrust grows the glutes, and it does so with little growth of the quads or adductors, which makes it a good targeted addition.
- Lunges Moderate evidence
Lunges (forward, reverse or walking) train the quads and glutes one leg at a time and highly activate the glutes.
- Leg extension Strong evidence
The leg extension isolates the quadriceps and is the best-supported way to grow the rectus femoris, the one quad head that squats and leg presses barely touch.