Sometimes, life simply gets in the way of exercise—deadlines keep you at the office, your kid gets the flu, or you just don’t feel like hitting the gym one day and that snowballs into several activity-free weeks. Regardless of what put the brakes on your training ambitions, you probably won’t be able to pick right up where you left off. Any hiatus from exercise has what experts call “detraining effects”—the loss of fitness gained during a consistent program (like your ability to run for a certain distance without losing your breath or power through multiple sets of weighted resistance moves). To try to figure out how soon you’ll get back in fighting form, you have to take into consideration how fit you were before your layoff and what type of exercise you had been doing. (Search: Reasons to exercise)
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“If you were in shape to begin with, you’ll still be fairly fit after your hiatus,” says Jeff Lemmer, PhD, an assistant professor in the Department of Movement Science at Grand Valley State University in Allendale, Michigan. In fact, well-conditioned athletes that have been training for a year lose just half of their aerobic conditioning after avoiding activity entirely for three months, according to a 2001 study published in the journal Medicine & Science in Sports & Exercise. And while a 50% loss might seem impossible to overcome, consider that new exercisers fare far worse. In a different study, beginners participated in a bicycling program for two months, making dramatic cardiovascular improvements and boosting their aerobic capacity substantially. The participants then quit exercise for the next two months and lost all of their aerobic gains.
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How quickly your fitness level deteriorates also depends on the type of workout you regularly perform. Unfortunately for those who regularly pound pavement, aerobic performance is the first thing to go when you slide into a slump. “You get a much faster detraining effect with aerobic exercise,” says Amy Crawley, MS, CSCS. “When you stop running, wait a week, and then start running again, your lungs hurt a lot more than your legs.” But, your capacity for cardio is also the first thing to kick back into gear when you resume your exercise regimen, she says.
Strength developed through resistance training takes longer to build than aerobic endurance, but sticks around a while—even when you’re not exercising. A 2000 study published in Medicine & Science in Sports & Exercise found that after nine weeks of training sessions, formerly sedentary study participants retained their strength gains for 12 weeks after ending their exercise program. What’s more, participants between the ages of 20 and 30 experienced only a 4 to 8% decrease in their one rep max on the leg press after a whopping 31 weeks off.
Clearly, cutting out exercise completely will lead to diminished performance. But squeezing in even one hour of exercise in a week will help you maintain your fitness. A 2002 study published in the Journal of Gerontology found that after completing three sessions of resistance training a week for 12 weeks, men who trained just once a week for six months were able to maintain the muscle strength and size they gained during their 12-week exercise program. To help maintain cardiovascular fitness, studies have shown that you need to exercise at 70% of your VO2 max at least once per week.
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Alas, if you are forced into an extended hiatus from exercise, ease back into it. Otherwise, you’ll put yourself in danger of injury, which will delay your return to peak fitness even longer. “Reduce your sets, reps, or weights by 10% if you’ve been out for two weeks—more if it’s been longer,” says Crawley. Listen to your body, suggests Femmer. While you don’t necessarily need to start from scratch, don’t assume you can eschew the re-training process and head straight for the heaviest weights or set out on the longest run. Use those first few uncomfortable workouts back as motivation to stick with your exercise program the next time you feel like taking time off.