Speed development vs speed endurance

Will there be a cross over between speed development and speed endurance? For example will a 100meter sprint above 95% aid speed development?

This is a one-way street. Greater Speed creates a greater Speed Reserve for a given Speed Endurance demand, as the differential has increased but Speed Endurance has little or no effect on maximum speed as Endurance is specific to the speed of execution (all the work in the world at 10MPS has no effect on the ability to achieve or maintain 12MPS. )

I am not arguing but why are sprints under seven seconds needed to develop speed. When you run a 100meters flat out are you not doing speed work for the first seven seconds and then tacking speed endurance work on the end?

I’d say that the main reason is you can’t do many hundreds in training without the quality diminishing rapidly. Therefore you run distances in earlier training cycles that address speed directly while gradually progressing to longer distances in later cycles. In later cycles you might run a hundred or two in training but the general idea is to develop speed first before you worry about enduring at speed. If the speed endurance work is done in too high a volume and too soon you are thereby limiting the quality of the speed endurance later. Certainly some of the highest speeds attained by many sprinters occur during 100m races but they just can’t do more than 1-2 without the speeds dropping off considerably.