@Fred__Duncan: In an 8-week study (Cahill et ...

In an 8-week study (Cahill et al. 2020), resisted sled pulls improved 5–20 m sprint times in every resisted group, while the unresisted group showed no change.

The heaviest loads (~75% velocity decrement) produced the largest gains in the first 10 m, along with the biggest

increases in horizontal force (F₀). Power (Pmax) improved across all resisted groups.

→ Lighter loads bias velocity/rhythm.
→ Heavier loads bias force and projection.

Both matter if you want balanced acceleration.

If you want to understand how to load resisted sprints,

when to use them, and how to integrate them into a system for speed, it’s all inside Speed Kills, my 80+ page eBook and sprint program built around the science of sprint development.

fredduncantraining.com/product/speed-…