It’s actually a function of the HPA axis called a neuro endocrine response. It’s not so much HEAVY weights as you put it as much as it is as difficult workout as you can stand to do. Most people lift “moderate or regular” as you’ve put it. Mostly for the mental fell good that they’ve “worked out”. But workouts are supposed to push you to what would feel like death. Simulating a hunt or being hunted that is life threatening. This with consistency yields the most natural testosterone production.