This is a VERY interesting topic to me personally… I’ve been a Strength and conditioning coach for the last ~12 years. And have competed at the national level in powerlifting. I started playing guitar when I was 18 since I didn’t like my roommates… Interestingly enough, MANY of the elite level athletes (not just average or slightly above average athletes) were involved in some sort of musical endeavor at some point during their development. I think there is a direct correlation between early music and athletic correlation but don’t have any specific data.
That being said being the nerd that I am in both strength and conditioning and guitar, I have noticed that the more consistent I am in training, the more relaxed and focused I feel practicing guitar. Since the 3 phases of lifting weights take place in different parts of the brain, there has to be some crossover. Whether it is in technical/mechanical processing or the ability to of the nervous system to better coordinate global/fine motor skills, there is definitely some carryover. Granted, I wouldn’t recommend anyone putting themselves through the stupidity that I did, but there seems to be benefit to training and its carryover to practice.
I have noticed that when/if I am deadlifting heavy, I have noticed it takes me longer to warm up my fingers when playing guitar. I also think there is a correlation between complex movements in the weight room and coordinative (is that a word?!) ability completing fine motor tasks. Again, no data on this just my empirical observation with myself and some of the high level athletes I have been blessed to interact with.
I do think that it takes more focus to stay relaxed playing guitar when you are lifting heavy as I can remember playing guitar when I was competing regularly and gripping the guitar like I was trying to choke it… If anyone is super interested in this, I’d be happy to try to sift through the mountains of “stuff” I have and see if I can come up with anything. I’ve got a bunch of really old translated russian manuals from the 60’s and 70’s. What I can say is that Americans have sport training and physical preparation pretty wrong! Hopefully someone got some use out of these ramblings…