Squat biomechanics simulator: femur length, lean and bar position

To stay balanced, the bar has to stay over the middle of your foot. Your thigh sits horizontal at parallel, so a long femur puts your hips a long way behind the bar. The only way to bring the bar back over the foot is to lean the torso forward.

That lean lengthens the hip moment arm — the horizontal distance from the hip to the bar — so the glutes, hamstrings and lower back do more of the work. A short femur does the opposite: a more upright torso and a more even share between knees and hips.

Each of these changes the geometry in the simulator, so you can see the effect before you try it:

• Let the knees go forward. A bigger shin angle moves the hips closer to the bar line.
• Raise the heels with lifting shoes or a small plate if your ankles limit knee travel.
• Widen your stance and turn the toes out. Seen from the side, an angled thigh is shorter.
• Try a high-bar, front or goblet squat, which keeps the load higher and further forward.

Leaning forward is not wrong. It is the normal result of your proportions, and you can still build big legs with it.

A low-bar squat sits the bar a few centimetres further down the back, across the rear shoulders. That shorter lever lets you lean further while keeping the bar over the foot, so low bar is usually more forward-leaning and more hip-dominant. High bar sits on the upper traps and is usually more upright and more knee-dominant.

A 2017 review in the Journal of Strength and Conditioning Research (Glassbrook et al.) reported a more upright trunk and greater knee demand in the high-bar squat, and greater hip demand in the low-bar squat. For the full lift-by-lift picture see the exercise comparison tool.

Mostly because of your proportions and how far your knees can travel. Fry, Smith and Schilling (2003) showed that stopping the knees from moving forward increased forward lean and raised the hip torque sharply while lowering the knee torque. If you lean more than you would like, check ankle bend first.

It is a 2D side-view lever model at parallel depth. Default segment lengths come from standard body proportions (Winter, 2009). Torque uses only the bar load, not the weight of your body segments. It does not account for hip socket shape, mobility, bracing or technique, and it does not judge whether a squat is safe.

• Winter DA (2009) Biomechanics and Motor Control of Human Movement, 4th edn. Wiley.
• Fry AC, Smith JC, Schilling BK (2003) Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res 17(4):629–633.
• Swinton PA et al. (2012) A biomechanical comparison of the traditional squat, powerlifting squat, and box squat. J Strength Cond Res 26(7):1805–1816.
• Glassbrook DJ et al. (2017) A review of the biomechanical differences between the high-bar and low-bar back-squat. J Strength Cond Res 31(9):2618–2634.