Often the catalyst for a well-intentioned new year health kick, the millions of fitness DVDs found in stockings around the world over Christmas may actually be causing considerable psychological harm to viewers.

That’s according to researchers at Oregon State University, who have warned that many fitness DVDs contain negative imagery and demotivating language.

Their study of 10 popular commercial exercise DVDs – published in the latest issue of the Sociology of Sport Journal – found that the imagery in the fitness videos may be perpetuating and reinforcing hyper-sexualised and unrealistic body images.

In addition, researchers found that one in every seven motivational statements on the DVDs was actually a demotivating statement that could reduce the effectiveness of the workout, diminish the user’s hope and potentially cause psychological harm.

“These findings raise concerns about the value of exercise DVDs in helping people develop and commit to a workout programme,” said Brad Cardinal, a kinesiology professor in the College of Public Health and Human Sciences at Oregon State University.

“There are a lot of exaggerated claims through the imagery and language of ‘do this and you’ll look like me'.”

The study found that most of the instructors and models were slim, female and white, and they typically wore revealing attire. According to Cardinal, this sends a subtle message about what people who are fit should look like and emphasises physical appearance as opposed to improved health.

Another finding was that 25 per cent of the language used by instructors was motivational, but one of every seven motivational statements could be considered negative. Such statements included phrases such as “say hello to your sexy six-pack,” “you better be sweating,” and “you should be dying right now.”

Cardinal said those types of phrases are dangerous as they focus on outcomes, encourage social comparison, and don’t take into account individual differences in health or fitness. He added that “tough love” phrases and strategies can also have a harmful effect because they can lead to injuries or other adverse health outcomes.

“Buyers should beware when making these purchases,” warned Cardinal, who said many of the instructors appear to have little or no credentials in fitness instruction.

“There are also questions about some of the exercises, which could lead to injuries and pose a real danger to the user.”