This is a grew questions. There are a few clients who actually blame their failures or lack of results on their trainers. Regressions and progressions happen to everyone, even us personal trainers. Like Frank said, trying to to overreact at a regression is very important step. Your client’s weigh gain after 6 weeks could have been caused by a multitude of reasons.
Here are few things to consider:
1) Remember, the progress of a client hinges on the both the trainer and the client. I make that cleat to all my clients at the onset. The client has a part to play in showing up for sessions punctually, adhering to nutritional guidelines and giving maximal effort. The trainer’s part is being early for sessions, of course, writing sound programs and disseminating helpful articles and publications to continually enhance client’s knowledge.
2) Keep in mind that 4 things are measure on a weight scale : muscle, fat, bone and water. A weight gain doesn’t necessarily mean fat gain because as we all know, muscle weighs more than fat. As long as strength training is involved (which I’m guessing it is), muscles will always have the ability to grow via hypertrophy.
3) Finally , have a sit down with this client. Find out if his/her eating patterns changed a little over that period. Maybe stress from work or family caused some over eating. Stress has been linked with the release of cortisol which causes weight gain. Thyroid problems and other hormonal issues have also been know to impact weight gain so find out if this client has any of those conditions.
I can almost assure you that one of these three tips, if not all, will address the issue.