I honestly believe the bench press may be the best weight training exercise for a 100m sprinter. I’m just drawing from my own experiances.
My sprint times never correlated all that well with increases in squat lifts for example.
But whenever the bench lift was in my program I increased my speed.
I don’t go to the gym anymore for various reasons and I don’t have a heavy duty powerlifting bench and olympic barbell at home.
I have since dropped all weights work and now do more running drills etc. (not a tip, as that bit’s not relevant to this thread for starters, but please read on.)
If I was able to add one weights exercise to my program it would be the bench press. (followed possibly by dumbell rows.)
Your muscle fibres in lower body are allready taxed from the running work. Any further training - even damage - may compromise effect on those fibres and what they are to adapt to. (Remember that most athletes at sub elite leval are so desperate to add leg strength that they often go overboard on reps x % of 1 rep max, exercise variaion and volume, in order to try and build strength, often making mistakes.)
The bench press however, is less likely to interfere with the most important fibres in running, but can still give a good stimulation to the central nervous system. (Most peoples bench is WAY over half of their squat.)
There are other factors in my opinion;
It is easier to recruit a large % of fibres from upperbody muscles in upper weights work, than same % of lower body fibres from lower weights work.
weights is a little better at developing upper body strength than lower body strength, yet another reason why upperbody weights work is easily as effective as lower weights work for the sprinter, in my opinion.
The stimulated c.n.s (stronger body) without further compromise on lower body, whilst developing upperbody strength directly -which in turn helps sprinting arm mechanics- which effects rest of body in sprinting - also helps improve rest of bodies strength etc.
I’m in no way the expert on this, but this is my logic and way of seeing it, plus like you, I have a lot of training experiance of differant programs over the years.
I’m sure Charlie or other may pin point the facts for you better if need be.