1. Flying blind

"Without a doubt, the foundation of many troubles people have in building muscle/getting fit is not using a program designed by a professional and sticking to it," says personal trainer Chris Bathke. "I've seen hundreds of guys over the years do the same chest, arms and abs exercises and get literally nowhere. If they had been working with a program that utilises the overload principle, periodisation and other facets of an intelligent, scientific program, then progress would be constant."

The problem: spend too long without seeing results and eventually you'll try something drastic and wind up hurting yourself.

Photo by Shutterstock Jul 20, 2012

How to injure yourself at the gym

We asked five personal trainers to pick the most common mistakes people make in the gym that lead to injury.