Within four weeks: Your strength will start slipping
Dr. Hameed estimates that some people will notice their strength declining after about two weeks of inactivity, while others will begin to see a difference after about four weeks. The silver lining: Our strength probably diminishes at a slower rate than our endurance, and one 2011 study in theJournal of Strength and Conditioning found that when one group of men stopped doing resistance training, they still had some of their strength gains up to 24 weeks later.
Within eight weeks: You might gain fat
Dr. Hameed estimates that people will start to notice a physical change—either by looking in the mirror, or at the number on the scale—after about six weeks. Even elite athletes aren’t immune to the rebound. A 2012 study in the Journal of Strength and Conditioning Research found that competitive swimmers who took a five-week break from their training experienced a 12% increase in their levels of body fat, and saw a boost in their body weight and waist circumference. (We should also point out that these athletes weren’t totally sedentary—they still did some light and moderate exercise.) And a 2016 study found that elite Taekwondo athletes who took an eight-week hiatus from exercise experienced an increase in their levels of body fat and a decrease in muscle mass, too.
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That said, there’s a difference between breaking up with exercise for good and taking a well-intentioned rest. The distinction: “You need to do some type of activity [every day],” says Dr. Hameed. For example, maybe you just ran the Chicago Marathon and can’t run another 16 miles, let alone 26—in that case, says Dr. Hameed, you should do some cross-training. (Think: cycling, using the elliptical, or even light walking.) Just don’t quit moving altogether—your body, brain, and waistline will thank you.