Some People Do Better Exercising At A Low-Intensity Pace

Liz Wolfert seemed a picture of health. The Denver-based financial consultant rode her bike to work, climbed "14ers" - mountains that rise more than 14,000 feet above sea level - took kung fu lessons and swam. But in 2015, at age 32, she learned that she had elevated blood glucose levels, a possible sign of pre-diabetes. Wolfert's first instinct was to work out harder and faster. But she soon learned that she needed to do the opposite: slow down and exercise at a much easier pace.

Wolfert was told of her "metabolic inflexibility" - and the recommendation of low-intensity exercise - by Inigo San Millan, director of the Sports Performance Program at the University of Colorado Sports Medicine Center in Boulder. An exercise physiologist who works with elite athletes, San Millan defines metabolic flexibility as the body's ability to quickly switch between fat and carbohydrates to fuel exercise.

Individuals with Type 2 diabetes are metabolically inflexible. That is, they have a poor ability to switch back and forth. Endurance athletes, on the other hand, have an amazing capacity to do so. Fats and carbohydrates are metabolized in the mitochondria, so mitochondrial function is the key element behind metabolic flexibility.

Elite athletes, San Millan explained, are incredibly efficient at this task because they have a high level of mitochondrial health. "Mitochondria have the job in cells of metabolizing carbohydrates and fats in order to generate energy," he said. "As a result, this is a population practically devoid of Type 2 diabetes."

The average person, however, may have a metabolism that is less agile. "If you are not metabolically flexible, you have a tough time accessing and burning fat for fuel," San Millan explained.

Wolfert learned this after a trip with her mother to San Millan's lab. "We read about his testing methods and that he was looking for average people to come in and try it," Wolfert explained. "We thought it might be a good idea to see where we stood and if it could help me with my" suspected pre-diabetes.

Both Wolfert and her mother expected her to exhibit better metabolic efficiency. "I am your typical deskbound American, not athletic, and don't exercise to the degree that Liz does," said Diane Wolfert, who is 66. "So we were shocked to see that I had good metabolic efficiency and Liz didn't."

One thing the mother got right that the daughter did not was exercising at a low intensity. "I do go for walks," said Diane Wolfert. "Based on my results, nothing needed to change."

San Millan has spent years testing the metabolic flexibility of elite athletes using high-tech and expensive methods. The standard test includes a muscle biopsy, which is not practical for widespread use.

Determined to broaden the test's accessibility, San Millan developed a streamlined version that he used on the Wolferts.

San Millan has patients exercise at gradually increasing intensity on either a bike or a treadmill wearing a mask that measures how efficiently they are utilizing fat and carbohydrates. "The test stresses the mitochondria to give us very clear signals of how well they work," he said. "I take periodic blood samples from the fingertip and assess how quickly the cells are clearing lactate, which is a metabolic byproduct that can lead to disease if it accumulates."

San Millan tested his methods to demonstrate their efficacy vs. the standard protocol, which involves a muscle biopsy, and it held up well, he said. "All the physicians I talk to love the concept of my test, and many refer their patients to us for metabolic rehabilitation."

Rosalie Naglieri, a Maryland-based clinical endocrinologist, finds the approach intriguing but suggests that multiple factors may be at play.