It is well-established that a regular exercise regimen is good for physical health and mental well-being. Physical exercise improves strength, stamina, mood and energy level, and also promotes better sleep habits. But an important part of any exercise routine is an appropriate amount of rest.

According to the Mayo Clinic, an appropriate amount of exercise time recommended for adults is 150 minutes a week of moderate aerobic activity, or 75 minutes a week of vigorous aerobic activity. Aerobic activities include walking, running and swimming. While some people spend more time that that at the gym, conventional wisdom among medical professionals and fitness experts stresses the importance of allowing the body to rest to maximize the gains made.

Robert Herbst, a powerlifting champion and weight loss and wellness professional, explains that recovery days are essential for building muscle. A lack of rest days can lead to injuries, he warns.

Excessive or improper training can lead to chronic inflammation within the muscles. Overtraining can also contribute to metabolic inflexibility, hindered performance and diminished the ability to lose excess body fat.

“As we say, you do not get stronger in the gym,” Herbst says. “You get stronger away from the gym recuperating. One gets fitter by stressing the body with exercise and allowing it to adapt and super-compensate to that stress so that it can deal with greater stresses on the future. In order to adapt, the body must be allowed to do that recovery.”

Recovery occurs when the body is allowed to rest, he adds. However, Herbst notes that some light exercise on rest days can benefit the body. Light exercise on recovery days have benefits over total rest them because it keeps the muscles stretched and a healthy supply of blood flowing to them.

Light exercise can also reduce the buildup of lactic acid in muscles. That occurs where there is not enough oxygen in the muscles that break down glucose and glycogen, which are used for energy.

Types of exercise that are beneficial on rest days are light cardio workouts, such as walking, leisurely riding a bicycle, swimming, yoga and stretching, the latter which can include resistance band training. Herbst also recommends rest days include some restorative modalities such as massage, and heat or ice treatments. He says proper nutrition, hydration and sleep are essential throughout the process.

Dr. Kristina Hendija, a family medicine practitioner and medical adviser to Beardoholic, says that while consistency with exercise is key to achieving long-term fitness goals, rest days are just as important. She notes the body needs time and rest to heal.

“Whenever you do intense physical activities, just think of it as micro-damaging your body, especially your muscles,” Hendija explains. “For your muscles to grow from the microscopic tears that your exercise caused, they need time to rest and heal. During your recovery days, you allow cellular repair. Otherwise, you won’t be as effective in your workout because you will constantly get sore muscles,” Hendija says.

Another points Hendija raises is that resting heart rate lowers during recovery days. She says it’s important to not push too much and put too much strain on the heart.

“Trust me, after your recovery day or days, your muscles will be stronger and you can endure more exercise than before,” she adds. “Rest days are important so that you don’t lose the will to keep pushing, either. Your exercise should make you feel better and healthier, not make you feel physically bad every day.”

Recovery days are just as important as the time spent working out. It’s these days where the body will ultimately see the gains worked so hard for.