Could you be more specific? What postural/mechanical changes are occuring with a 20% sled that don’t occur with a 10% sled?
The postural and mechanical deviations that occur during a ‘cut’ far exceed the differences that occur by adding a little weight to a straight line pull with a sled, wouldn’t you agree? I don’t worry about slowing the athlete down a little…all resistance exercises are slower than sprinting. Like CF used to say, work all parts of the curve.
Yes CF has said works all parts of the curve, but has he ever advocated heavy sled use? I think you are taking this quote a bit out of context.
Once the sled is heavy enough, you are going to effect the striking patterns of running and there is going to be excessive anterior lean of the torso and posterior pelvic tilt. I suggest filming your athletes to see.
And the difference between postural changes during a cut and the resistance of the sled is that the body is trying to align itself properly for a cut, while during heavy resistance, it cannot proper align itself due to the sled.
Have you charted or filmed the changes that occur with different sled resistances?