Years of being a PT lecturer taught me anatomy and physiology that has helped tweak exercise movements for better effect. Here is a good example of why knowing your attachments of a muscle is important. The relationship of the calf muscle and the hamstring group is very important for maximal stretch and engagement of either.
I also show the usage of rubber bands to add the extra element of increasing load during the peak force of the exercise. This prevents the muscles from relaxing and letting the joints take over.
Try these tips next time you do stiff leg deadlifts.