Most people can agree that you should train a muscle at least 2x a week for maximum growth..but can we push the envelope and go even more frequent?
Recent studies have shown people who train muscle groups 5x a week had a substantially greater muscle growth than training 1 or 2x a week most likely because fully body workouts can achieve significantly greater total training volume in terms of TOTAL work (sets x reps x weight).
When the amount of exercises or sets is split across more sessions, more work is able to be performed. Think in terms of working muscles...are you going to be able to perform the best set of back squats after 9 other exercises that worked those exact muscles? By splitting up the exercises across multiple days, each muscle group has time to recover. And with better recovery leads to better training days and being able to put forth maximal effort on each day.
The days of the bro splits are over. Long live high frequency training.
High Resistance-Training Frequency Enhances Muscle Thickness in Resistance-Trained Men (Zaroni et al 2018)