Hack Squat
The hack squat is a machine squat: you stand on an angled platform with your back against a padded backrest and your shoulders under pads, and the load travels on a fixed track as you squat down and stand up. It works the quadriceps above all, with the glutes and inner thighs helping, and because the back is supported it lets you load the legs heavily without balancing a bar.
Also called: Machine Hack Squat, Sled Hack Squat, 45-Degree Hack Squat · Equipment: machine · Pattern: squat
Step by step
- Step into the machine with your back flat against the pad and your shoulders snug under the shoulder pads.
- Place your feet about shoulder-width apart in the middle of the platform, toes turned slightly out.
- Brace your trunk, push up to straighten your legs and release the safety handles.
- Bend your knees and sink under control, letting the knees travel forward over the toes while your heels stay flat.
- Descend until your thighs are at least parallel to the platform, or as deep as your heels stay down and your back stays on the pad.
- Drive through the whole foot to stand back up, finishing with the knees straight but not snapped back.
- After the last rep, stand fully, re-engage the safety handles and step out.
- Back flat against the pad
- Heels down, push through the whole foot
- Knees over the toes
- Sink deep under control
- Drive the platform away to stand
In VALDA, these cues are one tap away on the exercise while you train.
What it trains
| Muscle | Role | Evidence |
|---|---|---|
| Quadriceps: vastus lateralis | Prime mover | B |
| Quadriceps: vastus medialis | Prime mover | B |
| Quadriceps: rectus femoris | Secondary | C |
| Gluteus maximus | Secondary | B |
| Adductors | Secondary | C |
| Hamstrings | Stabiliser | C |
| Erector spinae | Stabiliser | C |
Evidence grades: A = strong research base · B = good · C = limited · D = coaching consensus.
What goes wrong, and the fix
Heels lifting
Fix: Move the feet a little higher on the platform and keep the whole foot flat.
Hips peeling off the pad
Fix: Sink only as deep as your hips and back stay against the pad.
Knees caving inward
Fix: Keep the knees tracking over the middle toes on the way down and up.
Cutting depth short
Fix: Sink until your thighs are at least parallel to the platform on every rep.
Bouncing out of the bottom
Fix: Control the descent and drive up smoothly from the bottom.
Snapping the knees straight at the top
Fix: Finish each rep with the knees straight but not forced back.
What the research says
Muscle growth · first choiceGeneral fitness · first choiceStrengthRehab & prehabEnduranceFat loss & conditioning
- Range of motion — A meta-analysis found full-range training built more leg muscle and strength than partial-range training, and a 10-week squat study found full-depth squats grew the glutes and inner thighs more than half squats.
- Load by goal — Research comparing loads finds maximal strength favours heavier loads, while muscle growth is similar across a wide range of loads when sets are taken close to failure.
- Effort — Studies show sets that finish a few reps short of failure capture most of the growth benefit, and true failure adds only a small extra return. A fixed machine path lets many lifters take sets close to failure without balance limiting the set.
- Volume and frequency — Research links more weekly sets for a muscle to more growth, with diminishing returns. Around 10 or more hard sets a week has been associated with more growth than fewer than 5, and training a muscle about twice a week is a common way to spread that volume.
- Rest — In trained lifters, rests of about 3 minutes between sets have produced greater strength and size gains than 1-minute rests.
- Foot position — Lifters commonly place the feet higher on the platform to bring in more hip and nearer the bottom of the platform for more knee bend. There is no direct research comparing hack squat foot positions.
Swap it mid-workout
With VALDA Pro, FLEX offers alternatives like these when you swap an exercise mid-workout.
Log the hack squat in VALDA, with these cues one tap away while you train and your history for it in one place.
General information about exercise technique, not medical advice. If you have an injury or a health condition, your healthcare provider is the right person to ask.