So eic you sprint with both legs at the same time then?[/quote]
I’ve never really bought into the idea that because only one foot is in contact with the ground at any given moment while running we should be doing single-leg exercises.
First of all, single-leg exercises require a balance component that running simply does not. Thus, recommending single-leg exercises on the basis that sprinting occurs on one leg at a time is a bit like telling a cyclist that they must learn to balance on their bike standing still in order to become a better rider in motion. IMO, that time would be better spent elsewhere.
I am in the weight room to do strength train, not simulate the specific demands of the sport. As you noted, bilateral exercises will increase limit strength far better than unilateral exercises. I can take care of any specific adaptation by doing the movements themselves (i.e., sprinting and jumping).
Finally, unlike sprinting, most of the so called single-leg exercises actually occur on two feet (i.e., lunges, Bulgarian split squats). The only ones that don’t are single-leg DL’s, single-leg squats, and step ups.
I actually like all three movements, but all three are not ideal ways of building limit strength and may or may not enhance the specifics of sprinting/jumping form. They are also difficult to do in productive form (step ups especially).
I’d rather divide my training time between limit strength moves (squats) and exercises I know will enhance my sprinting and jumping form (actually sprinting and jumping). I am starting to see a consensus emerge on this point from many of the guys who are successful in speed/vert training, including Kelly Baggett, Frank Yang (DigitalAir), A.C. (SquatDr), and Colin (CoolColJ).
They all pretty much agree that the core of speed/vert training is (1) bilateral limit strength exercises (esp. squats), and (2) practicing jumping and sprinting. The rest is just icing, and is not absolutely necessary IMO.
That said, I like mixing in a single-leg exercise for a couple reasons. One, it provides a good deload for the spine/CNS while still allowing decent work for the legs.
Second, it helps ensure equal development between the two legs, whereas bilateral moves can mask disparities. Third, in the case of the Bulgarian split squat, it provides a nice stretch to my hip flexors that I can’t get otherwise.
Hope this helps.