If you think hitting the gym hard every day is the key to losing weight, you may be mistaken.
A new study has found that the body's ability to burn fat peaks at a certain level of activity as the body adapts, the Press Association reports.
Researchers in the US measured the daily energy expenditure and activity levels of more than 300 men and women over the course of a week for their investigation.
They found that above a certain threshold of activity, the extra work people put in had no effect on the number of calories they burned.
During the study, individuals classed as having "moderately active" lifestyles were found to burn around 200 more calories each day than most sedentary people. However, those who did higher levels of exercise saw no extra benefit.
Lead scientist Dr Herman Pontzer, from the City University of New York, said: "Exercise is really important for your health. That's the first thing I mention to anyone asking about the implications of this work for exercise.
"There is tons of evidence that exercise is important for keeping our bodies and minds healthy, and this work does nothing to change that message.
"What our work adds is that we also need to focus on diet, particularly when it comes to managing our weight and preventing or reversing unhealthy weight gain."
The research team noted that the results may go some way to explain why people who start rigorous exercise programmes to lose weight often see a decline in their rate of weight loss after a few months.