Yeah, yeah…
As an athlete - some 15-20 years ago, I competed in long jump and triple jump. Needless to say, there was lots of debate over single leg work. The result - an overemphasis on single leg work lead to lots of pelvic related issues, particularly with the SI Joint. I was living proof of becoming over-specific with the work.
My best performances were yielded following concepts that Charlie espouses. Keeping it simple with the exercises, generally stressing my body in the weight room through heavy bilateral loads - and the odd split snatch and jerk (although not considered a truly unilateral movement). The next step was doing the proper work on the track through sprinting and careful amounts of hopping (very careful), bounding and jump specific work (into the sand-pit).
I’m a big fan of the philosophy of… “Just because you can do something, doesn’t mean you should.” Having to run full speed down a hard runway (most of them were very hard), take off on one leg, then land back on that same leg - you figure out what works and what doesn’t in a real hurry. Single leg squats did piss all for the type of forces I was dealing with during long jump and triple jump.
I’m not going to read through more of the banter on here about specificity and what “should” work. I certainly found out what didn’t work and see these patterns all the time. I see coaches forcing athletes to do single leg squats all the time. These athletes have had back problems, meniscal injuries and even ACL problems. Seen with my own eyes. Posts on a forum will not change my opinion of what I have seen.
I posted a presentation on CF.com by Loren Chiu which covered the specificity problems related to over-zealous unilateral work. The biomechanics of it do not transfer as well as a bilateral squat. Loren has a PhD from USC and now teaches at the University of Alberta in the area of biomechanics.
For peripheral work, lunges and split jumps are fine. Single leg hops in moderation and combinations with bounding are good. For high intensity work and heavy loads, stick to what is safe. Why risk your life for pennies, when you can earn dollars doing things the right way (proven through the experience of knowledgeable coaches like Charlie and KitKat)!
BTW KitKat - I’m in discussions with the head coaches of the Canadian speed skating team. We are less than a year out from the 2010 Olympics and we have a number of world record holders and world champions in the group. You can bet I will be very careful in the application of loads and exercises at this point in their training!