I train based off of major exercise movements, so I hit some of my muscles pretty much every time I train. I rarely do isolation stuff though, perhaps that's the difference. My back receives a lot of work everytime I'm at the gym and it has responded with lots of growth and strength gain, so I'd say that the more frequently you can handle working a muscle the more gains you make. Of course this means you have to see how fast your body can heal given your natural healing rate, food intake, and rest levels, to determine what you can do, otherwise you'll just end up overtrained. Regards, Sensless