Debunking the Knee Over Toe Myth

'Don't let your knees go past your toes.'

For years, I repeated this to clients. It seemed logical, was supported by respected organisations, and appeared unchallenged in the literature.

Until I looked closer.

What Changed

During my MSc in Biomechanics, I came across research showing that restricting knee movement in squats reduced forces at the knee. Good news, right? Except it increased forces at the hips and lumbar spine.

Restrict motion at one joint and the force goes somewhere else. It has to.

This made me wonder: what happens during a split squat? More specifically, what happens to the trailing leg that everyone seems to forget about?

The Experiment

With access to a biomechanics lab, I tested two variations:

1. Traditional split squat: knee behind toes (7.6° ankle dorsiflexion)
2. Full ROM split squat: allowing forward knee travel (39° ankle dorsiflexion)

In the traditional version, the trailing leg absorbed over 100 times more torque than the leading leg.

In the full ROM version, this difference almost disappeared. The trailing leg experienced only about 1.5 times more torque than the leading leg.

As Tom Purvis pointed out: 'We are so busy worrying about the leading knee being in front of the foot, that we fail to see that the trailing knee is FAR in front of the foot.'

The Real Questions

This was a small experiment. N=1. But it showed me something about our tendency to reduce complex biomechanics to simple rules.

We pay too much attention to the motion and the position without looking for the line of force.

It's not about the relationship between the knee and the toes. It's about the relationship between the line of force and the knee joint.

So instead of asking 'is the knee past the toes?', we could ask:

• What are we actually trying to achieve with this exercise?
• Why are we avoiding knee torque if we're trying to strengthen knee extensors?
• Where is the force going instead?
• How do this client's structure and tolerance affect what's appropriate?

I no longer tell clients to keep their knees behind their toes. I assess their structure, their goals, their movement quality, and their force tolerance.

The 'knee over toe' debate taught me something. Our role isn't to memorise and enforce universal rules. It's to understand principles deeply enough to make informed, client-specific decisions.