Is the flat side up harder than the dome side up?

Yes. With the dome on the floor, the whole platform can tip, so balance is much harder to hold. In a study of track and field athletes doing loaded half-squats, standing on the flat side of an inverted BOSU produced more body sway than squatting dome side up, on foam or on the floor.

Will BOSU squats make my legs stronger?

Only a little once you are past the beginner stage. The unstable base limits how much load you can use, so leg strength is best built with squats on stable ground, such as the Kettlebell Goblet Squat or the Barbell Squat, while this version trains balance and control.

Can I hold weights while doing it?

A light dumbbell or kettlebell at the chest is fine once the bodyweight version is smooth and steady. Heavy weights and barbells are not worth the risk, because a fall with a heavy load is far more dangerous than the extra training effect.

Should I do it barefoot or in shoes?

Either works. Barefoot or flat, thin shoes give better feel for the platform, while a stable training shoe can help if your ankles feel unsteady. Avoid thick, soft running shoes, which add a second unstable layer under the foot.

How deep should I squat on the BOSU?

Go as low as you can while keeping the platform level and the knees over the toes. For most people that starts as a half squat and works toward thighs close to parallel with the floor as balance improves.

BOSU Squat (Flat Side Up)

What Is the BOSU Squat (Flat Side Up)?

BOSU Squat (Flat Side Up) is a compound exercise that primarily targets the quads and also engages the glutes, adductors, calves and core. It is an intermediate-level movement performed on an inverted BOSU balance trainer, with the dome on the floor and both feet on the flat platform.

Flipping the BOSU changes the challenge. With the dome up, the soft surface gives under the feet but the base stays put. With the platform up, the whole board can tip in any direction, so every shift in weight has to be caught by the ankles, knees and hips before the edge touches down. That makes this version clearly harder than the dome-up BOSU Squat, and it is usually the next step once that one feels steady.

The squat itself works much like a Bodyweight Squat: the quadriceps drive the knees straight, and the glutes and adductors extend the hips. The difference is the constant balancing. The peroneals and calves work to keep the platform level side to side, the glute medius keeps the knees from drifting in, and the trunk stays braced so the upper body does not add to the wobble. Most people also squat shallower and slower here than on the floor, because depth is limited by how much control they keep.

This is a balance and control exercise, not a strength builder. The unstable base limits how much load can be used, so it complements squatting on stable ground rather than replacing it. It suits people who already squat well on the floor and want to train balance, ankle control and body awareness, and it fits well in a warm-up, a balance block or a lower-body circuit. Build up with the dome-up BOSU Squat and by simply standing still on the inverted platform before adding the squat.

Muscles Worked

MuscleActivation

Vastus Lateralis: Primary
Vastus Medialis: Primary
Gluteus Maximus: High
Rectus Femoris: High
Adductor Magnus: Medium
Gluteus Medius: Medium
Peroneus Longus: Medium
Soleus: Medium
Biceps Femoris: Low
External Oblique: Low
Gastrocnemius (Medial Head): Low

Instructions

Place the BOSU dome side down on the floor with the flat platform facing up, near a wall or rack you can grab if needed.
Step one foot onto the platform to one side of the center, then carefully bring the other foot up to the opposite side so the platform stays level.
Stand tall with your feet about hip to shoulder width apart and toes turned slightly out. Clasp your hands in front of your chest.
Brace your core and fix your eyes on a point ahead of you.
Push your hips back and bend your knees to lower slowly, keeping your weight centered over the middle of your feet.
Keep your knees tracking over your toes and your chest up as you descend.
Lower until your thighs are close to parallel with the floor, or as deep as you can while keeping the platform level.
Press through your whole foot to stand back up, straightening your hips and knees together.
Repeat for the desired reps, then step down one foot at a time.

Common Mistakes

Uneven foot placement
Standing off center puts more weight on one side of the platform, so the edge tips down as soon as you start to squat.
Knees caving in
Letting the knees drift inward while rebalancing stresses the knees; keep them tracking over the toes throughout.
Squatting deeper than you can control
Chasing floor-squat depth on an unstable base usually ends in a wobble or a fall, so go only as low as you can keep the platform level.
Dropping too fast
A quick descent makes the platform lurch at the bottom; lower slowly enough to correct small tilts as they happen.
Loose trunk
Rounding forward or letting the chest collapse shifts weight toward the toes and makes the platform harder to hold level.
Adding heavy weight too soon
Holding dumbbells or a barbell before the bodyweight version is steady raises the fall risk far more than it adds training value.

Injuries

BOSU Squat (Flat Side Up) is a medium risk exercise when performed with proper technique. The squat itself is gentle on the joints at body weight, but the platform can tip without warning, so the main risks are falling off, rolling an ankle as the edge hits the floor, and the knees caving in while the body scrambles to rebalance.

The knees are not the weak link when the rep is controlled. A lab study of healthy adults doing bodyweight two-legged squats with each foot on the flat side of its own BOSU found lower kneecap joint force and stress than in the same squat on the floor at several knee angles. That does not cover a fall, which is the real hazard here.

BOSU's own guidance does not recommend standing on the platform side, so treat this as an advanced balance drill. Set up with a wall, rack or partner within reach, keep the feet evenly spaced either side of the center, and never add heavy weights or a barbell. If balance goes, step off to the floor instead of fighting to save the rep. If the platform will not stay level, regress to the dome-up BOSU Squat or practice standing still on the inverted platform. Once the squat is smooth for 10 to 15 controlled reps, progress to slower lowering, a short pause at the bottom or the BOSU Single-Leg Squat (Flat Side Up).

Stop if you feel sharp pain in the knee, ankle or lower back, dizziness, or if you lose balance repeatedly as you tire. Fatigue makes the platform harder to control, so end the set while your reps are still steady.

Overview

Primary Focus: Quads
Equipment: Balance trainer and body weight
Modality: Strength
Difficulty: Intermediate

Alternative Exercises

Frequently Asked Questions

Q: Is the flat side up harder than the dome side up?: Yes. With the dome on the floor, the whole platform can tip, so balance is much harder to hold. In a study of track and field athletes doing loaded half-squats, standing on the flat side of an inverted BOSU produced more body sway than squatting dome side up, on foam or on the floor.
Q: Will BOSU squats make my legs stronger?: Only a little once you are past the beginner stage. The unstable base limits how much load you can use, so leg strength is best built with squats on stable ground, such as the Kettlebell Goblet Squat or the Barbell Squat, while this version trains balance and control.
Q: Can I hold weights while doing it?: A light dumbbell or kettlebell at the chest is fine once the bodyweight version is smooth and steady. Heavy weights and barbells are not worth the risk, because a fall with a heavy load is far more dangerous than the extra training effect.
Q: Should I do it barefoot or in shoes?: Either works. Barefoot or flat, thin shoes give better feel for the platform, while a stable training shoe can help if your ankles feel unsteady. Avoid thick, soft running shoes, which add a second unstable layer under the foot.
Q: How deep should I squat on the BOSU?: Go as low as you can while keeping the platform level and the knees over the toes. For most people that starts as a half squat and works toward thighs close to parallel with the floor as balance improves.