What about pushing vs pulling a sled?
In my experience, sleds, even slightly heavy, cause significant tightness in the hamstrings if you are pulling them. I don’t necessarily mind that, but it is worth considering if you are running further than 10 yards. I find the mechanics change quite drastically (in a negative way) if you are pulling a heavy weight.
Alternatively, sled pushes seem to be a much better exercise at getting this specific strength if you want to use a heavier sled. In spite of the arms being locked/zombie style, the shoulders down look much better than most heavy pulling I see. I concur with Henk K. that it seems silly to analyze in isolation since it is essentially just analyzing whether resistance training alone can improve the 5-10m time of an untrained person. A bit silly really.
I think steep(er) hills can fit in there well. Charlie was one of the big proponents of the 10% rule, but the hill he uses in his GPP video is quite steep and causing much more slowing down than 10% (which would be less than .4 over 30m for a male). I generally dislike heavy sled pulling though for somebody already lifting and sprinting regularly.
