When I received my personal trainer certificate less than a handful of years ago, the message was pretty clear:
Train a muscle once week for maintenance, twice a week for muscle growth.
The landscape here, however, appears to be changing. Recent research now suggests that working a muscle 3 times a week will increase muscle growth of those muscles more than the previously recommended twice a week would. Yet, increasing the volume will not necessarily aid getting your pipes to exploding level. Keeping the amount of exercises and sets that you found work well for you the same, and spreading them out over three sessions within 7 days will yield the best results.
At least they found that in Norwegian powerlifters. It does make sense when you think about, though, right? Doing a workout once a week definitely doesn't feel as if anything is happening. Soreness comes back every session, you're not getting stronger and you don't look bigger. I always felt twice a week was about right to maintain, with maybe a little growth sprinkled in when doing it right. Based on how I trained the last few month with 4 sessions in a week but doing continuous splits so that every muscle group gets focused on three times a week, I find this research is spot on.
What's your experience with working out once or several times a week? What's working for you?
I found that when I was first starting more frequent lifting helped to not only build muscle, but to reinforce the routine and lifestyle change. During my peak I was hitting the gym (crossfit at the time) i was going approximately 5 times a week. Right now, I have been going 2-3 times and have been making or maintaining the majority of my strength gains. However my metabolic capacity is way WAY down.