CARIUS TRAINING GUIDE
Change your workout split when the current structure no longer distributes training effectively for your goals, schedule or recovery, not simply because it feels old. A different split can help when priority muscles or lifts need more useful exposure, sessions have become too long, recovery between sessions is poor, or progress has stalled under the existing distribution.
Before changing, determine whether the split itself is the problem. A plateau caused by unrealistic loading will not necessarily disappear because upper/lower became push/pull/legs.
When a split change is justified, preserve useful exercises and progression data where possible. Change the organization with a purpose rather than resetting the entire program.