The study, conducted by Professor Brett Martin, of the University of Bath's School of Management, and Dr Rana Sobh of Qatar University, interviewed 281 male and female undergraduates.
In the study, the researchers asked half of the participants to imagine a physically unattractive version of themselves they feared they might turn into.
Then, they asked the participants to either imagine a scenario in which they dramatically failed to keep to a fitness programme or one in which they dramatically succeeded.
The analysis of the study showed that those who had been asked to think about a dramatic failure to keep to the programme were motivated to keep on training because they were fearful of not looking good.
Those who were asked to imagine they were succeeding in getting fit became less motivated to continue at the gym because they no longer had this fear of not looking good.
The study reveals that fear of failure motivates people more than gaining some success, which demotivates them. This fear of failure is particularly strong when people feel they can already see signs of the feared self they are striving to avoid.
The findings reveal why marketing works or doesn't work for some products like gyms to get a better body or cosmetics to reduce wrinkles. "How consumers see themselves in the future has a strong effect on how motivated they are to keep using a product or service," said Martin.
"When people dwell on a negative future, fear motivates them, yet as they move away from their feared state - a flabby body, or a wrinkled skin - they become less motivated. "At that point, marketers should take advantage of another insight of our study - that of motivating people with a more positive outlook," Martin added.
Martin found that among those who were asked to think positively about their bodies, the other half of the 281 surveyed, being successful in keeping to the fitness programme made them even keener to keep going to the gym. Failing to keep to the programme demotivated them.
"Once someone moves away from their 'feared self' - in this case an unattractive body - because they are successful in the gym, they lose motivation, so highlighting thoughts of being unattractive is unlikely to work," said Martin.
The researchers found that 85 per cent of those who wanted to avoid a feared unattractive self responded to a scenario where they were failing in the gym by wanting to press on, compared with 65 per cent who were succeeding in the gym who were motivated to continue.
They found that 91 per cent of those thinking positively about their bodies responded to a scenario where they were succeeding in the gym by wanting to press on, compared with just 57 per cent of people who were failing in the gym and wanted to go on.