DB arm swings?
db arm swings are probably beneficial. I personally prefer plate swing - I like having the arms locked, feels safer for the shoulder. Plate swings was probably my favorite upper body exercise when I peaked my vert. I could feel the carry over tremendously to jumping.
regardless, bodyweight exercises are a must.. just like in jumping, where you are "throwing yourself with your legs" (Kelly B terminology), upper body exercises give you the ability to "throw your upper body". This results in some serious coordination, strength, power, etc. So for example, if you can do 1 pullup in 3 seconds, versus 10 pullups, each lasting on average 1 second, you now have significant strength, power, and conditioning gains for all muscles involved in arm swing (upward and downward).
so making those improvements, in combination with actually jumping - to tie it together, is definitely important.
important BW exercises = dip variations, pushup variations, pullups/chinup variations.
apart from that, beneficial barbell/dumbell exercises include bench, overhead press, push press, jerk/snatch etc.. jerk/snatch being far more technical, limited by a learning curve.
My personal preference was mostly BW upper & plate swings, occasionally throwing in some DB upper (bench/rows).
I remember a strength coach once said that the bench press benefits sprinting.... I don't see how that can happen. I mean, obviously you don't want to be a scrawny nerd up top where you can't even do 10 pushups....
bench press can be used as a tool just to stimulate the CNS.. so, some heavy bench press singles, or doubles etc, can really amp you up great & not have a detrimental impact on sprinting related muscles. If anything, bench itself can give you some more shoulder power, which is definitely going to be beneficial to the start/acceleration phase of a sprint.. short distance sprinters usually have very well developed upper bodies - for some it's natural, for others it's a bit natural + upper body lifting. Regardless, adding some upper body mass can help improve a powerful arm swing.
bench aint bad for sprinters/jumpers.. upper body mass is less important for jumping though - the strength needs to be there, but the mass doesn't. That mass itself can benefit a sprinter in the acceleration phase of a short sprint, during the lean.
One of the easiest things to do is simply look at elite level athletes in these various sports, you can learn alot just by the naked eye. And remember, if most elite olympians seem to fit a stereotype, ie, oly weightlifters having huge legs, or 100m sprinters being lean af & fairly jacked, then for the "normal trainee", trying to achieve a similar physique isn't such a bad idea. If someone has very weak natural upper body development but wants to get better at sprinting, it's probably a good idea for them to experiment with adding some upper body mass into their training regiment. It doesn't always work, leverages change / tendons / muscle fiber composition change the game, but it can still help. If I was going to get into oly lifting, I would make my thighs, glutes, and back/upper back enormous. To some degree, physique imitation can be effective.
