Hack squat: proper form, muscles worked and common mistakes

quadscompoundmachine

How to do it

Back against the machine pad and feet mid-platform. Descend past parallel with the knees tracking over the toes and press without snapping the knees straight; it biases the quads.

Muscles worked

Main muscle: quads. When it plans weekly volume, every set of this exercise counts in full for quads: the generator does not split it with other muscles.

Hack squat vs. leg press: what changes

On the hack squat you stand under the shoulder pads and the sled runs along an angled track: your torso moves with you as in a squat, but you do not have to balance a bar. On the leg press you sit or lie back and push the platform away from you, with your hips fixed in the seat. That is why the hack squat is closer to the barbell squat in how the knees and hips work, while the leg press lets you load more weight with less trunk involvement. With your feet low and close together, the hack squat loads the quads more; with your feet higher or wider, some of the work shifts to the glutes.

Choose it after your main squat to add quad volume when you're already tired, if you haven't mastered a bar on your back, or if free squats leave your lower back beat up. It also works as the main leg lift in a gym without a rack. Progress with sets of 8 to 12 reps, and add a one-second pause at the bottom before you raise the weight.

Check where the safeties are and how they release before you load up, and keep the shoulder pads seated firmly. If your heels lift, move your feet up a little on the platform.

Technical sheet

Movement pattern: Squat
Minimum level: Intermediate
Technical demand: Needs coaching
Fatigue it generates: High (1.5 out of 2.2)
Risk if technique breaks down: Medium

Peak tension in the stretched position

These are the values the generator uses to decide where the exercise goes within the session.

Recommended sets and reps

As a compound lift, it fits in 3–5 sets of 5–12 reps leaving 1–3 reps in reserve (RIR). Prioritize it at the start of the session, when you're fresh.

Common mistakes to avoid

Going so deep that your pelvis tucks and your lower back peels off the pad: the useful range ends just before that.
Not adjusting the seat and pads to your body: your joint should line up with the machine's pivot.
Cutting short the part of the range where the muscle is stretched: that is exactly where this exercise gives the most stimulus.

What the research says

Because it is a multi-joint lift, the 2021 review of the repetition continuum by Schoenfeld and colleagues leaves room to choose: both heavy and moderate sets build muscle if they finish near failure, but maximal strength needs some heavy work.

It loads the muscle in the stretched position, which is where several trials find more growth: more hypertrophy from seated than lying leg curls (Maeo and colleagues, 2021) and better quad results from training the long part of the range (Pedrosa and colleagues, 2022). So do not cut the bottom of the rep short.

You do not need to reach failure on every set: according to the meta-analysis by Refalo and colleagues (2023), stopping one or two reps short gives very similar growth. The generator prescribes it with RIR for that reason.

References

Schoenfeld BJ, Grgic J, Van Every DW, Plotkin DL. Loading recommendations for muscle strength, hypertrophy, and local endurance: a re-examination of the repetition continuum. Sports. 2021;9(2):32.
Maeo S, Huang M, Wu Y, et al. Greater hamstrings muscle hypertrophy but similar damage protection after training at long versus short muscle lengths. Medicine & Science in Sports & Exercise. 2021;53(4):825-837.
Pedrosa GF, Lima FV, Schoenfeld BJ, et al. Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. European Journal of Sport Science. 2022;22(8):1250-1260.
Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ. Influence of resistance training proximity-to-failure on skeletal muscle hypertrophy: a systematic review with meta-analysis. Sports Medicine. 2023;53(3):649-665.

How Hack squat compares with other quads exercises

Of the 16 quads exercises in the catalogue, ranked from least to most fatiguing by the values the generator uses, Hack squat is number 12.

With that fatigue it is best placed early in the session, while you are fresh, without stacking equally demanding exercises for the same group after it.

With different equipment, the same movement pattern offers 12 alternatives, such as Goblet squat, Dumbbell step-up and Static lunge.

Quads exercises with the same pattern as Hack squat, from least to most fatiguing.
Exercise	Equipment	Fatigue	Technique
Dumbbell lunges	dumbbells	High (1.2 out of 2.2)	Basic
Box jump	bodyweight	High (1.3 out of 2.2)	Needs coaching
Cyclist squat	dumbbells	High (1.3 out of 2.2)	Needs coaching
Bulgarian split squat	dumbbells	High (1.4 out of 2.2)	Needs coaching
Hack squat	machine	High (1.5 out of 2.2)	Needs coaching
Sumo barbell squat	barbell	Very high (1.8 out of 2.2)	Needs coaching
Paused squat	barbell	Very high (1.9 out of 2.2)	Needs coaching
Front squat	barbell	Very high (1.9 out of 2.2)	Advanced

Tension with the muscle stretched. Hack squat loads the muscle when it is longest. In the review by Kassiano et al. (2023), across eleven studies, full range of motion and partials performed in the initial part of the movement — with the muscle long — produced more growth than partials performed at the end.

On a machine. In the meta-analysis by Haugen et al. (2023), with thirteen studies and 1,016 participants, there were no significant differences in muscle growth between training on machines and with free weights.

References

Kassiano W, Costa B, Nunes JP, Ribeiro AS, Schoenfeld BJ, Cyrino ES. Which ROMs lead to Rome? A systematic review of the effects of range of motion on muscle hypertrophy. Journal of Strength and Conditioning Research. 2023;37(5):1135-1144.
Haugen ME, Vårvik FT, Larsen S, Haugen AS, van den Tillaar R, Bjørnsen T. Effect of free-weight vs. machine-based strength training on maximal strength, hypertrophy and jump performance: a systematic review and meta-analysis. BMC Sports Science, Medicine and Rehabilitation. 2023;15(1):103.

Alternative exercises

More squat exercises

Add it to your routine

Progrevia can generate a personalized routine that includes Hack squat based on your level, goal and available days.

Build your quads workout

Generate a full routine with the emphasis on quads and Hack squat among your preferred exercises. Free, no sign-up.

Build my quads workout

Not sure what to pick? The setup assistant walks you through it, one question at a time. Open the assistant

Frequently asked questions

What muscles does Hack squat work?

Hack squat mainly works the quads muscle group, plus synergist and stabilizer muscles depending on the variation.

How many sets of Hack squat should I do?

Between 3 and 5 sets per session, adjusting the total weekly volume for quads to your level (about 10–20 sets per muscle per week).

Should my feet be high or low on the hack squat?

It depends on what you want. With your feet lower and closer together, the quads get more of the work, but you need good ankle mobility. With your feet higher, more glute comes in and it's often easier on the knees. Start in the middle of the platform and adjust a couple of inches based on how it feels.

Create my free routine

Progrevia builds gym routines from your own data: periodization, RIR and week-by-week progression. Free, no card.