Why do people put so much emphasis on the squat. Isn't the p-chain just as important for jumping as quads? Also what do you guys think is the dl to squat ratio athletes should be aiming for (specifically aiming this at Lance and Adarqui!)?
The problems with the deadlift, specifically using it as your main lift to supplement vertical jump training, is a.) it starts from a dead stop, there is no reversal or amortization phase as there is in the squat b.) like Kelly said, the technique and individual levers and structures make it very easy for lifters to turn it into a low back dominant lift, or lift with very limited rom. c.) the limited quad activity (specifically bad in the case of 2 leg jumps).
Some people do well with deadlifts, and you can use a touch and go technique or starting at the top and stopping at mid shin technique to get around the dead stop, but depending on your structure you may still have several other issues with your technique being as beneficial as a squat to your jumping. I have always found that squats supplemented with rdl have been much better for this cause, trap bar deadlift is another good option with the extra quad involvement but we do them without stopping on the floor if vertical jumping is the goal.
Any type of lift that limits the quad activity (box squat or squat with very little forward knee travel, deadlift, etc.) is not going to be nearly as beneficial as as one with more balanced quad and pchain emphasis imo, specifically for 2 leg jumps. The squat is just a nice balance of the two when performed correctly for an athlete, and deadlifts or deadlift variations can supplement that really well.
Btw, if youre squatting deep enough, it is highly likely that your deadlift will go up along with your squat, if you only deadlift it is not as likely that your squat will go up in the same fashion.