I wonder about rep ranges and programming...
20 rep squats are more mental than anything else. I wonder if introverts have better focus over a longer period to do well at these higher rep ranges. Where as extroverts would be more likely to hit heavy low reps and move on to something else.
Programming? I'd think introverts would be drawn to programs like 531 or Christy's that have a slow progression with a few well chosen exercises that don't change often. While extroverts may be drawn to Westide or Split Training where they get to rotate lifts a lot and tinker often.