Exercise is an important aspect of maintaining a healthy, functional body, but there is also a time and place for letting ourselves rest.

I'm a personal trainer and many people are shocked to find out that I don’t exercise every single day. I’ve found that my workouts are much more enjoyable and effective when I can look forward to a relaxing day off. It can help boost your mental morale, kind of like what a Friday does at work. It’s also important physically: Allowing your body time to rest is a necessary part of an effective training routine. These days give you time to heal from the stress you’ve placed on your joints and muscles, prevent fatigue and burnout, and can even help you break through the difficult plateaus you may be facing.

Just how many rest days we need each week is not a one-size-fits-all model. One study found that it took 72 hours of rest — or 3 days — between strength training sessions for full muscle recovery, while research from the ACE Scientific Advisory Panel says that a recovery period could be anywhere from two days up to a week depending on the type of exercise. This number will vary based on certain factors like your fitness level, age and type of exercise and intensity of your workouts. So knowing your own body and it’s limits is essential to determining the amount of work and rest days you need each week.

In addition to scheduled rest days, there are other times when it may be best to sit it out. Here are some scenarios when you should consider hanging up your sneakers and giving your body a little R & R.

You’re really stressed

When your workload feels like it’s never ending and your schedule is overloaded with juggling work and family commitments, the stress starts to take a toll mentally and physically. While exercise can be a stress-reliever — it isn’t always. This is an important time to really listen to your body. When you exercise, you’re working hard to raise your heart rate. This puts added stress on the body and leads to your overall stress-load increasing. For some people, this can actually exacerbate symptoms. Especially if making it to the gym is another thing you’re trying to squeeze into an already jam-packed day.

On the other hand, exercise is one of the most common recommendations for stress reduction, as it stimulates the production of endorphins which make you feel good after a workout. And, it does work for many people. So if you do find that exercising works for you as a stress release and you feel better afterwards, then go for it. On particularly stressful days, you may want to consider swapping intense workouts for those that help your body wind down and relax like yoga or walking or jogging outside.

You’re sleep deprived

It’s common knowledge that sleep is essential, but yet, many people still don't prioritize it. If you aren’t getting enough sleep, hitting the hay (instead of hitting the gym) may be the best way to prioritize your health. Look at it this way: If you’re sleep deprived your body isn’t performing as highly as it could be. Exercising when you're running on empty also increases your risk of injury. So if you’re exhausted, the best thing you can do for your body is to get a good night of rest and get back in the gym the next day.

“Insufficient sleep is associated with decreased insulin sensitivity, reduced levels of a hormone associated with appetite suppression (leptin) and increased levels of a hormone associated with hunger (ghrelin)," says Lisa Cottrell, a licensed psychologist board certified in behavioral sleep medicine at Aurora Health Care. "Insufficient sleep and chronic sleep deprivation can increase activation of the sympathetic nervous system (activating the 'fight or flight' response) and affect cardiovascular systems, inflammation, immune responses and metabolism.”

In this way, getting to bed an hour or two earlier can be just as beneficial (if not more so) for not only your overall health, but your waistline, as hitting the gym. If you’re exhausted and burnt out, take it as a sign that your body needs some TLC and let yourself rest.

You’re feeling under the weather

If you aren’t feeling your best, the gym might not be the best place for you. But how sick is too sick to workout? One general rule I always share with my private clients is that if the pain is coming from above the neck, it’s okay to workout. If the pain is below the neck, skipping the gym is a good idea. The exception to this rule is if you’re running a fever. If you have a fever, exercise should be off the table. The work you’ll be putting in won’t be as beneficial because of the increased dehydration you’ll be facing.

Dr. Gustavo Ferrer, MD, founder of the Cleveland Clinic Florida Cough Clinic, advises that if you have a runny nose, nasal congestion, and/or a sore throat, exercising is OK. “You may consider reducing the intensity of the exercise. If you exercise for one hour, cut to 1/2 hour during those days,” he says. He does recommend avoiding the gym and exercise for the first few days of a viral infection like the flu and the common cold — not only for your own health, but also because this is the period when you are contagious to others. “Also avoid the gym if you have shortness of breath, severe cough, fever or wheezing,” says Dr. Ferrer.

You’re really sore

You may need to take some time off after a really intense workout, especially if you wake up the next day feeling extreme soreness or muscle fatigue.

Gregory Marcolin, PT, director of Physical Therapy at OceanView Rehabilitation, explains that the dull ache, soreness, and/or sickly sensation that you feel in your muscles following the performance of a new or restart of an exercise routine (specifically strength training) is referred to as Delay Onset Muscle Soreness or DOMS. “This is typically experienced within the first or second day following the workout session,” he says. “Although the exact cause for this sensation at a physiologic level is not fully understood, it is believed that a type of strengthening for the musculature known as eccentric — or lengthening — of a muscle while under stress may cause micro-trauma to the muscle fibers. The soreness that is experienced is the body repairing the muscular fibers in order for growth to occur for the future. Rest is needed in order for the body to repair the damage (however small) that has occurred.”

Pushing through soreness and exercising, instead of giving your body adequate rest, can be detrimental in a few ways. First, your body may take longer rest periods in order to heal, says Marcolin. There may be an ”inhibition of essential nature hormone production that is required to heal and improve muscular strength/function such as Human Growth Hormone (HGH),” he explains. You also may increase your risk of injury: “Musculature is simply soft tissue that has the ability to perform amazing things throughout the body. However, with continued breakdown of these fibers due to excessive and prolonged DOMS, further injury such as tearing can occur,” Marcolin explains.

You’ve just checked a marathon off your bucket list

If you’ve just completed a race or another strenuous athletic feat you’ve been training for, it’s time to take some time off and celebrate. It’s always a great idea to factor in how much you’ve pushed your body when you’re calculating your recovery time. You can think of it as: The more stress you’ve put on your body during the workout, the longer you should give yourself to recover.

But just how much time should you give yourself? Marcolin says that there’s not a clear-cut period of rest that’s recommended, and that a recovery period varies from person to person. “However, following long periods of extensive exercise, the body's metabolic system may be stressed to its limit, therefore it is advised for anywhere from a minimum of 3-7 days of complete rest, hydration and sleep. Active recovery is also recommended as it helps increase blood circulation needed for recovery." Walking, swimming, and light jogging are all activities that will get your blood pumping and help your muscles heal, without putting additional stress on the body.

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