Inclement weather can be a good excuse to put off the daily jog, but new research suggests that exercising in lower temperatures could burn off more fat than normal – at least when it comes to shorter bursts of high-intensity exercise.
In a study of 11 "moderately fit, overweight" adult volunteers, lipid oxidation – the technical term for burning fat – increased by more than three times during exercise in a colder environment of 32 degrees Fahrenheit (zero degrees Celsius), compared with a "thermoneutral" environment of around 70 degrees Fahrenheit (21 degrees Celsius).
Participants were taken through a set of standard workouts for high-intensity interval exercise (HIIE), also known as high-intensity interval training (HIIT), at each temperature: ten 1-minute cycling sprints at 90 percent effort, followed by 90-second recovery periods of cycling at 30 percent effort, with a cool down period at the end of both sessions.
"This is the first known study to investigate the effects of cold ambient temperatures on acute metabolism during high-intensity interval exercise, as well as postprandial metabolism the next day," write the researchers from Laurentian University in Canada in their paper.
"We observed that high-intensity interval exercise in a cold environment does change acute metabolism compared to a thermoneutral environment. However, the addition of a cold stimulus was less favourable for postprandial metabolic responses the following day."
When our bodies get active, they're better able to process nutrients and regular lipid or fat levels in the blood. To check the effect on the study volunteers, the researchers measured skin temperature, core body temperature, heart rate, and the amount of oxygen delivered to the quadriceps muscles.
The next morning – after a high-fat breakfast – blood samples were taken to check on insulin, glucose, and triglyceride levels, to figure out lipid oxidation rates again and to see if the benefits of the previous night had carried over.
While exercise in the cold increased lipid oxidation by 358 percent immediately afterwards, there was no substantial difference following breakfast the next morning (the "postprandial" period). In fact, glycemic response (the change in the body's blood sugar levels after eating) was better after exercise in the thermoneutral environment, as far as post-breakfast readings were concerned.
"[W]hile acute benefits seem to be present during acute HIIE in the cold, postprandial metabolic responses are less favourable when high-intensity interval exercise is performed with acute cold exposure," conclude the researchers.
With so few volunteers and just a couple of HIIE sessions, it's too early to draw sweeping conclusions from the study – but it is an interesting starting point for looking at how ambient temperature might affect fat burning during bursts of intensive exercise.
Previous studies have shown that HIIE is very effective at burning off fat – which is part of its appeal – and there's also an established link between body metabolism after exercise and how hot or cold the environment is. This new study combines those two fields of research to look for further correlations.
We know that exercise is crucial in staying well and reducing the risk of diabetes, liver diseases, cardiovascular disease and other health issues – so the more we know about what makes for efficient, beneficial exercise and what doesn't, the better.
The research has been published in the Journal of Applied Physiology.