An LSU powerlifting coach once told me to think of my arms as nothing more than a hook and lever when deadlifting the bar, and I think the same holds true when performing the clean.
For those who are somewhat inexperienced in the ways of explosively accelerating their body, the clean can cause the novice to attempt to muscle the bar to the shoulders by flexing the elbow PRIOR to completing full extension. Coach Hatch always says, “When the arms bend, the power ends.” This mantra holds true in ~98% of the population, but there are always exceptions when considering athletic adaptation (i.e. My slight jump backwards after extension).
A faulty start may cause an early arm bend in an effort to get the bar to the hip faster to make up for lost time and speed, which can also lead to the athlete completely missing the power position. Seen here is an early arm bend into a muted hip in order to rush under the bar. This can cause the athlete to bang the bar off the thighs, rather scooping/sweeping the bar into the hip with elbows extended while maintaining tension as the bar reaches the hips.
To facilitate elbow extension, we need to turn on the triceps, and relax the biceps. This is best done by using the “hook grip,” which will relax the grip and help the athlete differentiate the clean from what could potentially turn into really fast curl to upright-row. @brucebarbell’s cue for pointing the knuckles down is a fantastic way to rev-up the triceps, and inhibit the biceps.
A corrective exercise to really drive this home is a sequential clean pull from below the knee – above the knee – and ending at the hip in order to train the athlete to keep the bar close and rely on hip extension as the primary mover, NOT the arms. As with most relationships, a crushing grip will never produce the results we want, rather loosen your grip and let the rest happen. Your relationship with the clean is no different.