What is the proper descent speed on a squat?
The fastest speed at which you can stay in control of the movement. This includes maintaining proper positioning, keeping the bar path over your mid-foot, correct bracing patterns, keeping your knees out and tension in the hips, and much more. But the main point is the descent speed is dictated by if you can keep all the technical specifications of a squat in order. You may even notice with yourself that as the intensity increases, you start to slow the movement down a bit, which is very common. That is a natural reaction to make sure you stay in control of the weight, versus the weight controlling you. Lighter weights will be easier to control than heavier weights, so many times as you work up in intensity, descent speed will start to change. For some, they can almost dive bomb a squat and stay in proper positions, while others basically do a tempo squat. There is a benefit to speeding the eccentric up, as the elastic rebound is greater, but when the eccentric speed reaches a point where it compromises form, it is detrimental.
One of the first things I have my athletes do when there are technical breakdowns in the squat is to slow down the eccentric. If the eccentric loading process is correct, usually the concentric portion of the squat will follow suit. What commonly will happen with lifters is that during the last 1/4th range of motion during the eccentric, things will start to show an internal bias. Knees cave in, upper/lower back rounds, hips and knees push forward, and ankles pronate. Not always, but many times this can be fixed by slowing down the movement. A good tell is if a lifter has great form at lighter weights. If they do, that means they have the ability to hit proper positions in a squat, it’s just that at certain intensities that breaks down. And if that is the case, slowing down the movement can help to alleviate these issues.
The take home message is to only go as fast on the eccentric as allows you to maintain optimal movement quality. If you consistently experience breakdown in form, slow down the movement until you can maintain proper position and tension throughout the movement. But if you can speed up the movement, do so, as that elastic rebound will aid in strength if you can control the movement through the entire range.