If you work out the same total amount, splitting your muscle workouts to hit each group twice a week builds more muscle than doing it all in one day a week. Basically, spreading out your training leads to better muscle growth.

Our current analysis shows that splitting your weekly muscle workouts into two sessions appears to build more muscle than doing everything in one day. The evidence we've reviewed leans toward training each muscle group twice a week when the total amount of work stays the same. What we've found so far comes from reviewing the available research. We found that 38 studies support this approach, and 0 studies refute it [1]. When you spread your exercises across two days instead of packing them into a single session, your muscles seem to respond better. This happens because giving your body more time between sessions allows it to recover and adapt more effectively. We are still gathering more data, so this view may change as new research becomes available. If you want to try this, you can split your usual routine into two shorter sessions each week. For example, instead of doing all your chest and arm exercises on Monday, you could do half on Monday and the rest on Thursday. Keep the total number of sets and reps the same. This simple shift might help you see better results over time.