we had this issue when doing a research project with track sprinters
if you do from teh blocks, you will need a much longer rope than the distance over which the sled is pulled e.g. if doing 10 m reps with a few m decelaration phase, you may need a 20 m rope to be safe
in our strongman training we dont have a block to start from, but i am sure it will help move heavier loads initially
Justin