When it comes to cardiovascular fitness and muscle strength, the saying is true: use it or lose it. While regular exercise can improve heart health and increase strength and mobility, taking weeks or months off can reverse many of those benefits.
That doesn’t mean rest days aren’t important. In general, short breaks can help you recharge physically and mentally, but whenever possible, you should avoid overextending your free time so that getting back into the swing of things doesn’t feel too overwhelming or depressing.
“Your body adapts to the stimulus you give it,” said Dr. Kevin Stone, an orthopedic surgeon and author of the book “Play Forever: How to Recover From Injury and Thrive.” “Your muscles get used to the stress and the testosterone, adrenaline and endorphins: all the wonderful things that come with exercise. By eliminating them, the body begins a process of muscle loss.”
What does it mean to lose physical condition?
To understand the phenomenon of deconditioning, it is useful to reflect on how activity, and therefore inactivity, affects the cardiovascular system and muscular strength. Because regular exercise helps the body transport oxygen and nutrients to tissues more efficiently, one of the first things to deteriorate with inactivity is cardiovascular endurance, said Edward Coyle, professor of kinesiology and health education at the University of Texas at Austin.
After a few days of inactivity, the volume of blood plasma circulating in the body decreases, Dr. Coyle explained, causing a series of cardiovascular changes. After 12 days, studies show that the total amount of blood the heart pumps per minute decreases, along with the amount of oxygenated blood available to muscles and other cells, measured as VO2 max.
If you return to the gym at this point, you’ll only notice slight differences in your performance, Dr. Coyle said. Your heart rate may speed up a little and your breathing may become heavier as your body works harder to pump blood and oxygen to where they are needed.
Scientists have found that it is around three weeks that people experience the greatest changes in their ability to complete a workout, as the energy produced by mitochondria for muscle cells decreases significantly. “That means the exercise will be more fatiguing,” Dr. Coyle said.
Strength declines less rapidly than cardiovascular health. After eight weeks, inactivity finally begins to affect muscle size and strength. For weightlifting or strength training, the maximum amount you can lift decreases, as does the number of repetitions you can perform, Dr. Coyle explained. You’re also more likely to experience muscle soreness a day or two after training.
The degree to which each person experiences a decline in fitness depends on age, genetics, lifestyle, diet, and their previous level of fitness. Studies show that older adults lose physical fitness almost twice as much as those between 20 and 30 years old. And while those who exercise consistently for months or years may experience fitness loss at the same rate as recreational exercisers or weekend exercisers, athletes who start at a higher fitness level “have more to lose in absolute terms,” Dr. Coyle said.
What can you do to keep fitness loss at bay?
While the cardiovascular and muscular changes that occur after prolonged rest may seem dramatic, the good news is that most people do not eliminate all activity in the same way that participants are often instructed to do in an exercise study.
If you have to travel or stay home because of bad weather, doing something is better than nothing, Dr. Coyle said. Swap out dumbbells for bodyweight exercises. Try small exercise “snacks” throughout the day, take the stairs whenever you can, or, better yet, aim to do some short, high-intensity interval workouts.
“If you spend just a few minutes a day doing interval training, that’s enough to keep your blood volume up and your mitochondria relatively up,” Dr. Coyle said.
If you are a competitive athlete, reducing the intensity or frequency of training just before or after a big race or match can be beneficial, as long as you do it intentionally. For example, many athletes plan a two- or three-week taper to give their bodies time to replenish their glycogen and allow their muscles to recover.
Those who need longer breaks can try cross-training or switch to another sport, such as skating or swimming. Or perhaps focus on improving balance with aerobics or dance classes to keep the same muscles active in different ways.
“Overall physical fitness is a combination of many factors,” Dr. Stone said. “It’s not just about muscle strength and cardiovascular fitness.”
How long does it take to make a return?
If you haven’t been physically active in a while, don’t despair. Just as off-seasons are common in any sport, getting in shape is also possible, and easier, for those who exercise regularly.
Research shows that although prolonged breaks significantly reduce fitness, most people who exercise remain ahead of those who have been sedentary all their lives. For example, while muscle fibers may shrink during long breaks, they don’t disappear completely and retain a molecular “muscle memory” that can help them recover months after stopping exercise. In other words, you are now prepared to regain strength and endurance much faster than at the beginning.
“You can regain about half your fitness in 10 to 14 days with moderately intense workouts,” Dr. Coyle said.
After this initial retraining period, the time needed to regain pre-rest fitness may vary depending on how long you need to recover. One study found that older adults needed less than eight weeks of retraining after a 12-week break. Other evidence suggests that competitive athletes may need to train for double to triple the amount of time they took rest.
To get back in shape, start by setting a goal to train for a set amount of time each day, without worrying about your strength or intensity, Dr. Coyle said. Once you can comfortably walk or jog 30 minutes a day for two to three weeks, you can begin to increase your pace to running. If you want to return to lifting weights in the gym, start with a lighter load and then gradually increase.
Many personal trainers recommend not increasing your pace more than 10% each week. But instead of sticking to an arbitrary number, adapt your routine based on how you feel.
If you can’t afford several weeks of retraining or simply want to get fitter faster, you can do more intense workouts or incorporate interval training to speed up the process. “The higher the intensity,” Dr. Coyle said, “the faster the rebound.”
