So I recently acquired a client who wanted to work out three days a week.

Wonderful, I thought: three days a week is a good amount of time to get something done. True, you might not be able to do everything you'd like in three hours a week, but it's a good base from which to work, and if people are watching their diet and staying off the couch most other days, they're going to see some good progress pretty quickly.

A couple of weeks into our work together, I asked this client--let's call her "Emily"--what she'd done since I saw her last. I know she has a very active dog, and that she had recently started jazz-dance classes, but she responded, "No, I've done nothing since I saw you last."

Now, Emily is a friend of my wife's, and the reason I'd asked is that my wife had told me that Emily was actually hiring two trainers--myself and another guy--as well as the private dance coach. Her plan was to work out five days a week and on two of those days, do a dance class two other days as well.

Oddly, she had decided to withhold from either trainer the fact that she was working with someone else. So for about three weeks, this other trainer and I had been working with Emily under the assumption that she wasn't doing any strength training outside of our sessions with her.

So for awhile there, I was baffled why Emily was experiencing knee pain and seemed so fatigued during our relatively mild workouts.

Once she came clean as to what was going on--something she found agonizing to do, as she felt she was double-timing me and this other trainer--I adjusted her program accordingly. Hopefully the other trainer did too.

I don't imagine anyone reading this will have this problem, but just in case: share with your trainer openly about what you're doing outside the gym. If he/she is worth a lick, he/she will work with whatever those activities are. If you don't, there's a possibility--perhaps even in probability--that you'll get injured.