New research suggests that high-intensity interval exercise may help burn more fat when performed in cold weather. The first-of-its-kind study is published ahead of print in the Journal of Applied Physiology. Regular physical activity improves the metabolism of consumed nutrients and helps regulate lipid (fat) levels in the blood. Previous research has shown that high-intensity interval training is better for lipid metabolism and oxidation (burning of fat) than moderate-intensity continuous exercise. Ambient temperature also plays a role in metabolism during exercise and while at rest, but it is unclear how temperature affects blood lipid levels or post-meal metabolism the next day. In a new study, a small group of moderately fit, overweight adult volunteers participated in two evening high-intensity exercise sessions separated by a week. In both sessions, the volunteers completed 10 one-minute cycling sprints at 90% effort. A 90-second recovery period of cycling at 30% effort followed each sprint. At the end of the sprint session, the volunteers were allowed to cool down with slow cycling or walking. In one exercise session, the ambient temperature was “thermoneutral” at approximately 70 degrees F. A thermoneutral environment is warm enough that it does not alter metabolic processes. The room temperature in the other session was a cold 32 degrees F. The researchers measured the participants’ skin temperature, core body temperature, heart rate and amount of oxygen delivered to the quadriceps muscles in the thigh during both sessions. Glucose (blood sugar), oxygen and carbon dioxide levels, and gas exchange rates were also recorded. After each workout, the volunteers ate a protein- and carbohydrate-rich nutrition bar before going to sleep. The next morning, the research team provided the participants with a high-fat breakfast, after which blood samples were taken to measure insulin, glucose and triglyceride levels and to compute lipid oxidation rates. “The present study found that high-intensity exercise in the cold increased lipid oxidation by 358% during the exercise bout in comparison to high-intensity exercise in a thermoneutral environment,” the research team wrote. However, longer term metabolic responses after eating the high-fat meal—including blood sugar regulation, fat burning and triglyceride levels—did not change substantially after the cold condition. Source
