Pause Back Squat
AKA Pause squat, stop squat
The pause back squat is a simple variation of the back squat that focuses on strength in the bottommost range of motion and rate of force development.
Place the barbell behind your neck—retract your shoulder blades tightly and rest the bar in the meat of your upper traps. Place your feet between hip and shoulder width with the toes turned out so that at full depth each thigh and the corresponding foot are in line with each other. Set your back in a complete arch, take in a large breath, and lock it in, forcefully tightening all trunk musculature. Bend at the knees and hips simultaneously to move down as directly as possible into the bottom of the squat with an upright posture, maintaining tension on the legs throughout the movement and controlling the speed of the descent. Full depth is achieved when the knees are closed as much as possible without losing the arch in the back (if you cannot sit into a full depth squat, you need to work on mobility). Upon reaching the bottom position, hold tightly without bouncing or moving for 2-3 seconds (or whatever time has been prescribed). Stand as aggressively as possible directly from the bottom position without first bouncing, again with the knees and hips together to maintain your upright posture—try to lead the movement with your head and shoulders.
For a lot more information on the execution of the back squat, and squat in general, see the following articles:
A pause of 3 seconds is adequate to eliminate the stretch-shortening reflex entirely. Longer holds can be done for additional posture strength work (i.e. trunk strength), but will not increase the effect on rate of force development.
The pause back squat can serve a few purposes. First, it helps train rate of force development in the squat by eliminating the stretch-shortening reflex that normally occurs and helps the muscles generate more force and momentum to recover through the sticking point of the squat. It will also improve trunk strength and postural strength, improve flexibility and comfort in the bottom of the squat, and help correct improper movement in the squat such as leading with the hips.
Pause back squats can be programmed in the same way as back squats, although usually reps above 5 are not recommended. Most common are sets of 2-3 reps.