This is a great foundational exercise but can double as much more. In young athletes, it teaches proper squat technique in regards to the pelvis and spine, and the kids find out how much mental toughness they have, fast. It's pure hell, and it's the last thing our athletes do on Fridays before they go home. In fact, they often crawl out of here!
The holds are between 45 and 60 seconds and we do them for 3-4 sets. The better you become at this movement, the more gravity just keeps assisting you into a deeper hold. You'll soon see some dramatic changes in hip mobility.
For anyone looking for size, loads and long times under tension can provide a great breeding ground for some new muscle.
Spread the floor apart with the feet. Drive the knees out while constantly pulling yourself down using your hip flexors and abs.