The best workout split for fat loss and muscle building depends on how much you can recover , not how many days you want to train. For most adults, the most effective options are full-body training 2–3 days per week  or an upper/lower split 4 days per week . More complex splits only work when recovery, sleep, and nutrition are fully dialled in. If you’re unsure which split is right for you, this guide will help you choose the one that actually produces results — not burnout.