The nice thing about CrossFit is that if you train at an affiliate you’ll have a trainer correcting your position.

Butt down! Knees back! On your heels!

Everyone knows these cues but it’s not readily apparent why they matter on a biomechanical level.

Here’s a very simple way of thinking about position:

1) contractile force increases as tension increases

2) tension is a derivative of muscle length

3) your position affects your ability to lengthen muscles

The important thing to note here is that you can lengthen your muscles past the point of optimal tension. Check out the picture above. When your muscle elongates beyond a certain point, tension decreases and you become weaker.

Being able to feel where you are on that curve is a very important intangible skill. Mastering that skill will make you instantly stronger.

Here is a very quick and easy example that will help you feel this skill. From a 3/4 squat position (thighs above parallel) let your knees drift in until they’re between your feet. Now push your knees out until they’re outside of the edges of your feet. You feel weaker in the first position because your hamstrings and glutes are slack.

P.S. For a fascinating glimpse into the history of biomechanics and exercise science check out A. V. Hill’s 1938 paper “The heat of shortening and the dynamic constants of muscle”