what causes it?

[KingDosia]

I think it may depend if you're lifting them slowly or quickly (plyometrics)

Thats not what Plyometrics are Matt try again.
thread still closed by the way

[kwill7]

Personally, lifting weights has helped my handspeed. The problem is the results arent instantaneous. Immediately after lifting for a couple of weeks or so you will actually feel slower. This is because youre muscles are sore and weakened from being broken down by the weights. After they have fully healed in a couple of weeks you should feel faster and stronger before. This is why fighters lift early in training camp so they have time to recover before the fight.