By Dr. Mercola
Most exercisers skip a workout occasionally. You may be traveling, fall ill, or have an unusually heavy work deadline that keeps you from the gym. Sometimes you simply may lack the motivation to work out, which may lead to another skipped workout or two.
Skipping workouts is not the same thing as spacing your workouts appropriately. In the case of high-intensity interval training (HIIT), for instance, you should only do it two to three times a week, max, because the intensity is so high. Your body needs rest in between to recuperate.
If skipping workouts becomes a habit, however, your body and your fitness level will suffer, with negative changes occurring faster than you might think.
How Long Does It Take to Get Out of Shape?
There's no hard and fast rule about how long it takes to lose your fitness edge. Generally speaking, if you're very fit to begin with, your body will remain in a fitter state longer than someone who's not fit, even as your workouts cease.
That being said, a study in the Journal of Applied Physiology suggested that skipping workouts for just two weeks can significantly reduce your cardiovascular fitness, lean muscle mass, and insulin sensitivity.1
Dr. James Ting, a board-certified sports medicine physician with the Hoag Orthopedic Institute in Irvine, California told CNN it can take two months or more to completely fall out of shape if you stop exercising.2
Two months to lose all of your fitness gains is fast enough… but there are varying opinions on the matter. Many experts agree that about two weeks is a pretty standard number after which your body will start to fall out of shape with no exercise.
However, coach Pete Magill, six-time masters national cross-country champion, told Shape you can lose up to 50 percent of your fitness gains in a single week of inactivity.3
Cardiovascular Fitness Typically Fades Faster Than Muscle Strength
When you skip too many workouts, the strength of your heart and lungs will fade first. One study found that after just 12 days without exercise, VO2 max, a measure of cardiovascular endurance, dropped by 7 percent, while blood enzymes associated with endurance performance dropped by 50 percent.4
Likewise, four weeks of inactivity among endurance cyclists resulted in a 20 percent decrease in VO2 max.5,6 Keep in mind this is among trained athletes… among those new to exercise, gains in VO2 max completely disappeared after four weeks of inactivity.7
The opposite holds true for strength loss among newbies, with studies showing newly made gains in strength tend to hold on even after months of inactivity. For instance, among previously untrained men who engaged in a 15-week strength-training program, taking a three-week break in the middle had no impact on strength levels at the end of the study.8
As for muscle strength among athletes, it appears to hold steady even after a month of inactivity – but there are significant differences among certain types of muscle fibers. Your body has three types of muscle fibers: slow, fast, and super-fast twitch muscles.
Slow-twitch muscles are the red muscles, which are activated by traditional strength training and cardio exercises. The latter two (fast and super-fast) are white muscle fibers, and these are only activated during high-intensity interval exercises or sprints. As reported by Greatist:9
"Medicine and Science in Sports and Exercise published a review of several studies on the subject that looked at runners, rowers, and power athletes.10 For all of these groups, muscular strength fibers appear not to change, even after a month of inactivity.
But here's the kicker: While general strength doesn't change much in that period, specialized, sport-specific muscle fibers start to change in as little as two weeks without a workout.
For example, endurance athletes lose a significant amount of the extra slow-twitch muscle fibers that they worked so hard to accumulate, and the same thing happens for the power athletes and their hard-earned fast-twitch muscle fibers."
Long-Time Exercisers Have an Easier Time Bouncing Back
If you've taken a long hiatus from the gym, you might be nervous about returning to your workouts. You should ease back in gradually to avoid injury, but if you're a life-long exerciser, you'll have an easier time getting back into shape than someone who only recently started.
Your age also plays a role. The older you get, the faster your muscles atrophy if you're not regularly engaging in appropriate exercise. In addition, it will take you longer to gain it back. When comparing 20- to 30-year-olds with 65- to 75-year-olds, the older group lost strength nearly twice as fast during six months of inactivity.11
That being said, if you're past your 30s, please don't let that discourage you. Older adults can gain a two- to three-fold increase in strength after just three or four months of weight training.
Are You Skipping Your Workouts Because They Take Too Long?
If time is the factor leading you to skip workouts, here's a simple hack you can use: cut down on the duration of your workout while increasing the intensity. Exercise experts are quickly abandoning the old exercise advice – the recommendations that suggest you need 30 or 60 minutes of moderate-intensity activity to best stay in shape.
Study after study is showing that this is not the best way to exercise, both in terms of its health benefits and its duration. You can actually reap much greater benefits by exercising in short, high-intensity bursts known as intervals than you can exercising for longer periods at a slower steady pace.
High-intensity interval training research presented at the Integrative Biology of Exercise VI meeting in Colorado, for instance, demonstrated that high-intensity interval training (HIIT) burns more calories in less time – a mere 2.5 minutes, divided into five 30-second sprint intervals at maximum exertion, each followed by four minutes of light pedaling to recuperate, can burn as many as 220 calories.12
Another study published in the Journal of Obesity reported that 12 weeks of HIIT not only can result in significant reductions in total abdominal, trunk, and visceral fat, but also can give you significant increases in fat-free mass and aerobic power.13 Other research published in the journal Cell Metabolism showed that when healthy but inactive people exercise intensely, even if the exercise is brief, it produces an immediate measurable change in their DNA.14
Several of the genes affected by an acute bout of exercise are genes involved in fat metabolism. Specifically, the study suggested that when you exercise your body almost immediately experiences genetic activation that increases the production of fat-busting (lipolytic) enzymes.
Yet another study found that unfit but otherwise healthy middle-aged adults were able to improve their insulin sensitivity and blood sugar regulation after just two weeks of interval training (three sessions per week).15 A follow-up study also found that interval training positively impacted insulin sensitivity.
In fact, the study involved people with full-blown type 2 diabetes, and just ONE interval training session was able to improve blood sugar regulation for the next 24 hours!16 The HIIT approach I personally use and recommend is the Peak Fitness method, which consists of 30 seconds of maximum effort followed by 90 seconds of recuperation, for a total of eight repetitions.
How Much Time Should You Rest Between Workouts?
While most people suffer from lack of exercise, once you get going, it can be addictive and some people do end up exercising too much — either by exercising too intensely, and/or too frequently. However, a really important part of creating optimal fitness is recovery. An equation to keep in mind is that as intensity increases, frequency can be diminished.
For example, as a weak beginner, you can do high-intensity exercise three times a week and not put much stress on your system. But once your strength and endurance improves, each exercise session is placing an increasingly greater amount of stress on your body (as long as you keep pushing yourself to the max).
At that point, it's actually wise to reduce the frequency of your sessions to give your body enough time to recover in between. In fact, you need to allow your body to fully recuperate in between sessions in order for the exercise to remain productive. Remember that, as your fitness increases, the intensity of your exercise goes up, and the frequency that your body can tolerate goes down. As a result, you need to continuously customize your program to your own fitness level and other lifestyle issues.
As a general rule however, you do not want to do high-intensity interval training exercises more than three times a week. High-intensity strength training can be done twice a week initially, but as you get stronger you will need more recovery time and eventually drop down to once every 7-10 days. Any more than that and you'll put your body under too much strain.
With High-Intensity Exercise, Less Is More
One of the major benefits of high intensity exercises is that it allows your body to produce human growth hormone (HGH), commonly referred to as "the fitness hormone." However, as explained by Dr. Doug McGuff in a previous interview, once you're fit, you really don't need frequent spurts of growth hormone production.
At that point, recovery actually takes precedence as being more important, and your recovery period could be anywhere from three to seven days. In fact, he strongly recommends NOT exercising too frequently once you are in fit condition, and here's why:
"[Y]our adrenal gland… sits right above your kidneys, and it's arranged in layers. On the outermost layers, you have mineral corticoids that control your sodium and your electrolyte levels. In the middle layer, you have your corticosteroids that control sugar and generate stress hormones.
And in the innermost layer is where you generate growth hormones and the sex steroids, or that's involved in the axis, in the feedback loop that generates that. The old saying in medical school to memorize the three layers is 'salt, sugar, sex' – the deeper you go, the better it gets.
But you got to remember, your adrenal gland is an integrated organ. Those three layers are not perfectly divided. If through high-intensity exercise you're trying to hammer that adrenal gland three times per week, but now you're much stronger and your body hasn't fully recovered from your Monday session and you come back and hit it again on Wednesday… you're going to tap down into that deeper level. Instead of growth hormones spurt, you're going to get in a cortisol spurt. You're going to completely undermine what it is that you're after."
When Should You Skip the Gym?
One of the benefits of being fit is that you can take time off and recover and use the reserves that you have built up to help you recover. It is kind of like having stored fat during times of famine. One time to rely on those "reserves" is when your body is under stress from being sick. You'll generally want to seek rest as your body mobilizes to fight off the illness, but you'll need to listen to your body to know for sure.
If you have enough energy to tolerate it, increasing your body temperature by sweating from exercise will actually help to kill many viruses. Over-exercising will place more stress on your body, however, which can suppress your immune system, so you should keep the intensity of your workouts on a moderate level if you're sick (such as taking a brisk walk). It's generally advised that you avoid exercise if you have symptoms that are "below your neck," such as:
- Coughing or chest congestion
- Widespread body and muscle aches
- Vomiting, upset stomach, and/or stomach cramps
But no matter what your symptoms, you need to be very careful and listen to your body. If you don't feel up to it, and all you want to do is get some rest, then that's what your body needs. And I can't stress enough that if you don't feel well, you should not do your full, normal exercise routine, as that could clearly stress your immune system even more and prolong your illness if you are not careful and wind up overdoing it.
High-intensity exercise like Peak Fitness should be avoided when you're sick, because any kind of intensive exercise boosts production of cortisol, a stress hormone that inhibits the activity of natural killer cells—a type of white blood cell that attacks and rids your body of viral agents.
This is why running a marathon can actually increase your chances of getting sick shortly thereafter. In fact, elite endurance athletes can suffer anywhere from two to six times as many upper respiratory infections during a year compared to average, active individuals.17