Nick already called out Sprint Geezer on one of his videos. Don't know if anyone mentioned that in this thread yet, but he has come to this site and read this thread already.
So here is what I have to say for Nick seeing that he's finally training somewhat right and not doing those pointless 800s.
The 100 is a step in the right direction towards the best training on the planet, and that's linebacker training.
How is the training going for the 100? Getting faster in the 40? Here's some tips. Make sure you keep your arms relaxed as much as possible. Limit the back swing as much as possible. The 90 degree arm angle is a flawed concept from the 1930s that is still taught today.
You want to keep your hands as close as possible to your face at all times. Don't allow the hands to drop below your chest at any point.
Even during the so called back swing. This will increase turnover..Limit lactic acid buildup because you're not straining yourself.
Make you more relaxed. And allow your legs to move more efficiently and smoothly down the track.
Try this technique and let me know how it goes. It works. Pivot the arms from the shoulders, not the elbows. Limit the back swing.
Don't actually do a back swing. Focus on smootly pivoting from the shoulders and the main thing is not allowing the hands to drop below the chest at all times. Let me know how this goes.
So overall your elbow angle should be like 20 degrees. Keep your hands as close as possible to the shoulders as you can. Do not swing the arm open from the elbow at all.
I included a video on how to do this right.
https://www.youtube.com/watch?v=pgceYHKT7_k