According to a study conducted at the University of Liverpool in the U.K., just 14 days of inactivity can cut our fitness level by 4 percent. “It took 14 days of training to see fitness levels return to what they were at before the sedentary period” writes Jordan Smith in Runner’s World.
When the researchers measured participants’ fitness level, after they were asked to stop doing workout (who otherwise walked 10,000 steps per day), the discovered that “their cardiovascular function decreased by nearly 2 percent and VO2 peak decreased by 4 percent, leading to an overall fitness levels drop of as much as 4 percent”.
… their metabolic health took a dip, too: Their total body fat increased by 0.5 percent, waist circumference by one-third of an inch, and liver fat by 2 percent. They also became more insulin resistant, a condition where your body does not respond as readily to insulin as it should, causing excess blood sugar to build up in your bloodstream and raising your risk of type 2 diabetes.
Kelly Bowden Davies, Ph.D., professor of Sport and Exercise Science at Newcastle University, U.K told Runner’s World “When you stop exercising, your muscles contract less frequently, and you reduce the activation of an enzyme called AMPK, which aids blood sugar absorption for fuel”.
The lack of shear stress, or the heavier force of blood flow on vessel walls during exercise, may contribute to poorer blood vessel health. That’s because the more you exercise—and get your blood pumping—the healthier your heart and arteries will likely be.– The Runner’s World
The researchers found that “after the participants resumed exercise, the researchers again tested their fitness levels 14 days later—the same amount of time that they rested—and found that they had returned to their baseline”.