bro there is no right and wrong way to pair muscle groups in my opinion. i mean sure there are secondary muscles being used in every lift you do. for examlpe chest. if you work your chest like me heavy then your tris get hit hard to. anyway the thing for me is i completely change my lifts every 6 weeks. for example weeks 1-6 day 1 bis tris, day 2 shoulders traps and abs, day 3 hams and calves, day 4 chest and abs, day 5 back, day6 quads, and day 7 off. then weeks 6-12 might be day 1 back and bis, day 2 hams and calves, day 3 off, day 4 chest and tris, day5 quads and shouldersand calves. no matter what i try to keep my muscles confused as not to get muscle memory. if i feel they arnt i will either change lifts or routine muscle paiiring all togather.