In the basic form, the restricted single leg concentric box squat with a leaning backward (2nd pull OL position) cannot be carried out to a balanced position and one must fall back on to the box where there should be ample padding. Being a scientist that never looks to prove the null hypothesis I found this to be the only exercise that gave substantial results in the early acceleration phase.If one needs to restrict that knee from moving beyond the toes one could employ another box that stands in front of the knee.
As one gets more advanced, the restricted single leg squat (etc. etc. etc) can be executed to a more balanced position by moving up on to the toes a little but the thigh-shin-foot angle must be preserved.
It sounds like it’s somewhere between an old-school bodybuilding sissy squat using a specialized sissy squat machine and a leg extension. I’m leary any time natural movement (especially joint translation and rotation) is restricted.
You can call it Lombard’s paradox (hip extension)that I’m trying to facilitate but the previously mentioned sports scientists never referred to it as that probably for fear of intimidating the readership with big words.
They talked about rectus femoris as a hip extensor? I can’t say I’ve ever heard of it working that way. I’ve heard of biceps femoris acting as knee extensor and hip extensor but nothint with RF.
The one-quarter effectiveness is taken from the study by Delecluse et al. (1995) who measured every inch of movement with a velocimeter. They also used a very large number of subjects which likely would have given the study a lot of power. Delecluse quoted a significance of p<0.05 between plyometrics and strength training in that regard. I actually underquoted the results which show the ratio to be more one-sixth.
Do you have an abstract for the study? I'm not familiar with it. Are you saying that they found plyometrics to be 6x more effective than strength work at improving speed?
From my own calculations, the plyometric programs that have a net horizontalness (more horizontal based exercises than vertical) have produced the greatest improvements.
In most North American coaching circles the emphasis is on vertical plyos.
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