1/ Charlie, can the CNS be stimulated positively by varying the sprinting surface or footware?
I noticed that when running bare footed or in thin soled flats on the track, for warm-up I experienced what I would term neural fatigue, yawning, sleepiness and lethargy akin to the after effects from speed training.
2/ Is there another way of stimulating the CNS without using the bench press as an upper body exercise. Does any other upper body exercise equate to the BP in recruiting the CNS?
The CNS CAN be stimulated differently by varying the surface and footwear- but this is not adviseable close to a meet. I’m sure you can use other upper body exercises for CNS stimulation, but the BP is the safest way to generate the highest relative stimulus.
You can control CNS load by varying the surface. Sprinting on grass lowers the CNS load vs muscular work, as, of course, do hills, and every change in surface hardness moves up the ratio of CNS load vs muscular load
As Gloop points out, you stop the speed work if you hear an increase in footfall sounds as this is an indicator that the hip is dropping before you can actually see it.
As you say, the CNS has a finite envelope so lifts drop in numbers as the sprint intensity rises. Can you describe what you mean by percentages? Lift max? Relative to each other? Relative to speed vol?