It might be time to stop trusting your treadmill, at least if you're hoping to lose weight.
The fat-burning measurements on exercise machines aren't accurate, and the right exercise for weight loss may be highly individualized, new research suggests.
Researchers from the Icahn School of Medicine at Mount Sinai looked at 26 participants in a small study, comparing their heart rate data and how efficiently they burned fat during clinical exercise tests.
They found that the ideal heart rate zone for optimal fat burning differed widely between participants.
However, most commercial exercise machines, and many classes, recommend a "fat burning zone." Using factors like age, gender, and heart rate, machines like a treadmill or exercise bike will recommend a target percentage of your maximum heart rate to maintain, which you can then keep an eye on with a heart rate monitor. In a fitness class, a wearable heart rate tracker might serve a similar purpose.
But researchers found those target heart rate zones rarely predicted how well people actually burned fat while working out.
As a result, the one-size-fits-all approach is likely not helpful in aiding individuals with their weight-loss goals, according to the study published last month in the journal Nutrition, Metabolism, and Cardiovascular Diseases.
Future studies could help identify a better way to predict how people can most efficiently burn fat during exercise, and trainers may be able to use exercise tests to help clients find their ideal exercise and heart rate target, the researchers wrote.
"People with a goal of weight or fat loss may be interested in exercising at the intensity which allows for the maximal rate of fat burning," lead author Hannah Kittrell, PhD candidate at Icahn Mount Sinai, said in a press release. "However, the typically recommended fat-burning zone has not been validated, thus individuals may be exercising at intensities that are not aligned with their personalized weight loss goals."
For now, the best way to find best type of exercise for your body is to work with a qualified trainer to consider your goals and experience, alongside other lifestyle factors like your diet and schedule, fitness experts previously told Insider.
Don't rely on just cardio — weight lifting can help burn fat, too
A common misconception about the fat-burning zone is that cardio is the best or only option.
But previous research has found that resistance training exercises such as lifting weights can be just as effective for weight loss. It may even be more helpful than cardio alone in the long-term, since strength workouts can help build muscle to boost your metabolism over time.
And for living a long, healthy life, a combination of cardio and strength training may be best, some studies suggest.
Diet may be more important for weight loss than exercise, some research suggests
If weight loss is a big priority, you may want to focus more on what you're eating than what you're doing in the gym, according to some scientists.
Evolutionary biologist Herman Ponzer previously told Insider that diet may be more important than exercise for long-term weight loss. His research suggests that the human body can adapt to exercise-related weight loss by causing your metabolism to compensate elsewhere. For example, after a hard workout you might move less during the rest of your day, burning less energy overall, or you might feel hungrier and eat more to make up for the energy burned.
However, there are still major benefits to exercise that have nothing to do with weight loss. Plenty of evidence shows exercise is great for your health, helping improve energy, boost mood, and stave off dangerous illnesses like heart disease and cancer.
