I wrote a post last year about online personal training. (I even used this same image. Efficiency!) In a nutshell, I'm not convinced it can work well without at least some in-person sessions.
However, it's still a big thing on the internet, largely because it can be easy and profitable for trainers to implement. Still, I was a bit disturbed to see this article directed at personal trainers on the topic of online training. Some of it is fine, but this part in particular bugs me:


The scale is the dreaded measuring device most commonly used to check changing body composition; that is, are you getting fatter? It's not a good measure, though, since it doesn't really tell us anything about body composition--the ratios of fat, muscle, bone, and water that make up total body weight. Water can be particularly confounding since one cup weighs about half a pound, so drinking a beverage or using the bathroom can immediately change results in a measurable way. What we're really interested in is body fat percentage--that's the most useful measure of body "comp."

