High intensity training increases testosterone and stress hormones (cortisol, norepinephrine).

We've also developed inhibitory measures to these stresses, via social learning, so that we normally don't start hammering on random cars or pouncing on those we're racing with. These behaviors too very likely have correlates at the level of brain chemistry.

Causation is a big deal. Hormonal surges won't cause anyone to behave in any way but they do make aggressive acts more likely, yes. So yeah, it's good to work on your conflict negotiation and relaxation skills while you're taking your training up a notch.