Nov. 4, 2000016

 

Evidence shows that physical exercise helps you build a brain that not only resists shrinkage as you age but also increases cognitive abilities.

Exercise encourages your brain to work at optimum capacity by causing your nerve cells to multiply, strengthening their interconnections, and protecting them from damage. There are multiple mechanisms at play here, but some are becoming more understood than others.

The rejuvenating role of brain-derived neurotrophic factor (BDNF) is one of them. BDNF activates brain stem cells to convert into new neurons. It also triggers numerous other chemicals that promote neural health. Further, exercise provides protective effects to your brain through:

• The production of nerve-protecting compounds
• Improved development and survival of neurons
• Decreased risk of heart and blood vessel diseases
• Altering the way damaging proteins reside inside your brain, which appears to slow the development of Alzheimer's disease

Promote Intelligence and Better Mood With Just 20 Minutes a Day

A number of neurotransmitters, such as endorphins, serotonin, dopamine, glutamate, and GABA, are also triggered by exercise. Some of these are well known for their role in mood control. Exercise, in fact, is one of the most effective prevention and treatment strategies for depression.

BDNF and endorphins are two of the primary factors triggered by exercise that help boost your mood, make you feel good, and sharpen your cognition. So, how much do you have to exercise in order to maintain a sunnier disposition and better memory long-term?

According to a 2012 study published in the journal Neuroscience, the "secret" to increased productivity and happiness on any given day is a long-term investment in regular exercise.¹ And a little each day appears to go further than a lot once or twice a week.

"Those who had exercised during the preceding month but not on the day of testing generally did better on the memory test than those who had been sedentary, but did not perform nearly as well as those who had worked out that morning," the authors noted.

The reasons for this can perhaps be best perceived visually. Take a look at these images, showing the dramatic increase in brain activity after a 20-minute walk, compared to sitting quietly for the same amount of time.

It's hard to think of a downside to exercise, but if there were one it would be this: most of its benefits are not permanent.

While there is evidence that people who exercise for decades may experience fitness and health gains in later life, there's also evidence that some of those hard-earned benefits may disappear if you stop exercising.

How long does it take for your body to "notice" that you've stopped hitting the gym? Experts suggest just about two weeks and in some areas even less.

Here's What Happens to Your Body if You Stop Exercising: The Two-Week Mark

You probably expect that your muscle tone will take a beating once your workouts stop, but less expected changes will occur throughout your body. One of the first places to experience the repercussions may actually be your brain.

Research published in the journal Frontier in Aging Neuroscience revealed that endurance runners who skipped exercise for 10 days had reductions in blood flow to their brain's hippocampus, which is a region associated with memories and emotions.²

After about two weeks, meanwhile, your endurance may suffer, which means you may find yourself slightly more winded if you need to quickly climb a few flights of stairs. This is because of changes to your VO2 max (also known as maximal oxygen intake).

VO2 max is defined as the maximum volume of oxygen you can utilize in one minute of maximal or exhaustive exercise,³ and it's used as a measure of endurance.

Time magazine spoke with Dr. Farah Hameed,  a sports medicine physician with Columbia Doctors in New York City, who noted that your VO2 max may fall by about 10 percent after two weeks without exercise, 15 percent after four weeks and 20 percent after three months, conservatively.⁴

Further, while exercise is well known to offer benefits to blood pressure and glucose levels, these benefits are among the first to go if you skip too many workouts.

For instance, one group of people who'd been exercising regularly for eight months lost nearly half of the well-earned improvements to their blood glucose levels when they became inactive for two weeks. (On the other hand, they still retained 52 percent of the benefit, which speaks to exercise's powerful benefits.)⁵

Loss of Strength and Weight Gain: The Four- to Eight-Week Marks

If your workouts take an even longer hiatus, you can expect increasingly noticeable changes to your body, both physically and aesthetically. You may start to notice your strength slipping after about two or four weeks with no activity. And after about six to eight weeks, you may start to gain weight. For instance:⁶

• Competitive swimmers who stopped exercising intensely for five weeks gained body fat and had increases in body weight and waist circumference⁷
• Taekwondo athletes who stopped exercising for eight weeks had increases in body fat and decreases in muscle mass⁸

In the case of the elite taekwondo athletes, the training break did suppress physiological stress, which shows there's a fine balance between giving your body needed rest to recover from your workouts (especially high-intensity workouts) and taking too long of a break, which starts to negate some of exercise's key benefits.

If You're a Seasoned Athlete, Do the Benefits of Exercise Last Longer?

It would seem logical that someone who's been exercising for decades may take longer to become de-conditioned than someone who's an exercise newbie. However, there's some conflicting research in this area. For instance, four weeks of inactivity among endurance cyclists resulted in a 20 percent decrease in VO2 max.^9,10 Among those new to exercise, however, gains in VO2 max completely disappeared after four weeks of inactivity.¹¹

On the other hand, studies show 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.¹²

Long-time exercisers do benefit in the time it takes them to bounce-back after an exercise hiatus, compared to newbies. 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.¹³ Even among older adults, however, it doesn't take long to see benefits from regular workouts; older adults can gain a two- to three-fold increase in strength after just three or four months of weight training.

How Long Should You Give Your Body a Rest Between Workouts?

This depends on a number of factors, including your age, fitness level and goals, and type of activity. Be aware that exercising too intensely and/or too frequently should be avoided. A general rule is that the more intense the exercise, the fewer times a week you should do it.

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 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.

On your "off" days, while you don't want to engage in more high-intensity activity, you can and should engage in other types of activity, such as walking, stretching or flexibility training. You needn't be sedentary on your off days. In fact, you'll benefit from getting physical activity virtually each and every day; you simply need to change up the intensity and type.

There Are Times When You Should Skip a Workout

Skipping workouts generally isn't recommended — unless you have one of these five valid reasons for not working out.

Why Are You Skipping Your Workouts?

If you're in the habit of skipping workouts often, realize that the only person you're hurting is you. Exercise has the potential to help you feel better mentally, physically and emotionally. It can rid your body of stress and lower your risk of chronic disease. Regular workouts will help you to stay focused, think clearer and get sick less often. So what's not to like? It does take time, commitment and hard work, which is why the exercise programs that last will be those you find most enjoyable.

Pick a time of day that works for your schedule (this may change from day to day) and pick the mode that you prefer. Some people thrive on going to the gym. Others prefer to exercise at home. You may enjoy exercising in group classes or with a buddy, or you may prefer to work out alone.

In addition to your HIIT sessions, try to incorporate regular strength training, flexibility work, core work and stretching. You can also get creative with your activities and add in dance classes, yoga, sports leagues, gardening and any other active endeavor you enjoy.

The key word is enjoy. The more you look forward to your workouts, the more likely you are to keep doing them. As an added bonus, most people feel great after they workout, which provides additional motivation to keep going. If you don't feel good after your work out — for instance you feel exhausted instead of energized — this is a sign that you may be exercising too much and need to take more time for recovery.

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