If The Shoe Fits

In this week's Rundown, researchers tackle long-term weight gain, the soft versus firm running shoe debate and cardiorespiratory exercise for teenagers.

The Rundown

Weighty Matters. New research from exercise scientists at Brigham Young University offers a startling picture of obesity in the United States. The team examined the long-term weight gain of more than 13,800 U.S. adults who were randomly chosen as part of the National Health and Nutrition Examination Survey (NHANES), an annual CDC-sponsored survey that looks at a nationally representative sample.

The researchers found that more than half of the adults gained 5% or more body weight over a ten-year period. For over a third of them, the weight gain was 10% or more body weight and almost a fifth of the sample population gained 20% or more body weight over a ten-year period.

Using the NHANES data, the researchers also discovered that ten-year weight gain was significantly greater in women than in men (12 pounds on average for women compared to 6 for men) and the greatest gains in terms of age were found in young and middle-aged adults.

The study’s lead author, Larry Tucker, warned that “the U.S. obesity epidemic is not slowing down” and hopes that the team’s research will help health care providers focus more on at-risk individuals.

If The Shoe Fits. The complex link between running shoes and injury has been the subject of numerous studies over the last few years, particularly when it comes to soft versus firm cushioning. In 2020, Laurent Malisoux of the Luxembourg Institute of Health conducted a trial with 848 runners who were assigned either firm or soft cushioned shoes and found that the runners wearing the firmer shoes were 52 percent more likely to develop an injury.

But, measurements from the force-sensing treadmill revealed that the runners wearing the soft shoes had greater peak impact forces, meaning they hit the surface harder, which you would expect would cause more injuries.

To address this puzzle, Malisoux did a study this year to discover why soft cushioned shoes, despite the greater impact, were causing less injuries. He found the answer in the timing of the impact. Soft cushioning slows the timing of your lower leg decelerating as it hits the ground. This overlaps with the timing of the larger force that is delivered a few milliseconds later by the rest of your body.

Together, the two impacts make the total force appear greater in softer shoes. When Malisoux separated the impacts, he found that the lower leg deceleration impact (the one linked to injury) was actually less in softer shoes than it was in firmer shoes.

In theory then, soft cushioned running shoes should reduce leg impact and injury but Malisoux notes that many running shoes with plush cushioning also contain a stiff carbon-fiber plate in the midsole and its effect on injury is untested.

His advice is to stick with what you’re running in if you’re satisfied with it and if not, try several different designs before making the transition. “Each runner is unique,” he says, “and the shoe that works well for your friend may not fit your foot.”

Teen 20. A new study published in the journal, Pediatrics, suggests that teenagers’ cardiorespiratory fitness may benefit the most from 20 minutes of vigorous exercise a day.

Over a two-year period, the researchers followed 339 teens, aged 13 and 14, who wore wrist-trackers while participating in school-based exercise programs that focused on running.

The study found that the teens maximized their cardiorespiratory fitness at 20 minutes of intense running and exercising longer did not improve it. The researchers note that only cardiorespiratory fitness was assessed, and other aspects of teens’ health may improve from lower intensity exercise.

Replay

This week’s vintage moment in fitness culture is brought to you by Arnold Schwarzenegger on his way to winning his fifth Mr. Olympia title, 1974.