u/Effective-Fox-2087

This will sound immature but me and my buddies have a group where we compete for weekly strain. I’ve noticed I have to do significantly more than other people to get a high amount of strain. Me and my buddy could do the same thing and he would get 15 I would get 10 etc. could this be a product of us just being in different body shapes, or is it an issue with my HR zones? Would appreciate any help