Indeed, T.R.E. therapy targets the psoas muscle to relieve tensions / stress hormones accumulated there. The body-tremors that are provoked used to be a classic reaction that animals still manifest after acute stress but that we humans lost due to culturization.
I myself tried it several times. Often the first 2 days, my symptoms got considerably worse, with nightmares and high stress levels, but then i used to go back to normal. Does that mean i have released an amount of stress hormones? I don't know but it sounds plausible.
The tremor-reaction is quite intense for me, so that i 2x injured myself with a strain in a muscle, which forced me to give up.
Big coincidence: i started again 2 days ago, but the reaction was too strong: massive POIS-symptoms the day after. Not feeling very comfortable with going on now (while that probably is what i should do)