Exercise is Medicine Q&A

1. What’s the basic exercise recommendation for adults? 

At least 150 minutes a week (two and a half hours) of moderate-intensity exercise or l75 minutes (one hour and 15 minutes) of vigorous-intensity aerobic activity a week. Aerobic activity should be performed in episodes of at least 10 minutes at a time. For more extensive health benefits, five hours of moderate-intensity activity or two and a half hours of vigorous activity. In addition to the aerobic stuff, muscle-strengthening activity (resistance training) at least twice a week.[1]

 

2. What is “moderate” activity? What’s “intense?”

The subjective way to distinguish these is simple: With moderate activity, your breathing quickens, but you’re not out of breath. You break a light sweat after about 10 minutes. You can talk, but not sing.

With vigorous activity, your breathing is rapid and deep. You sweat after only a few minutes.  You can only say a few words without pausing for breath.

More objectively, you can use your heart rate to gauge activity level. First, figure out your maximum heart rate. The simplest way is to subtract your age from 220. If you’re 74, for instance, your maximum heart rate is 146 – that’s the maximum number of times your heart should beat in a minute during exercise. Moderate exercise activity gets you to 50 to 70 percent of your maximum heart rate; vigorous activity gets you to 70 to 85 percent.[2]

 

3. How can you determine your “fitness age?” 

Short of having a cardiac stress test on a treadmill at a medical institution, you can make some reasonable estimates with a few simple measurements at home. One way is to use the online methodology developed by researchers at the Norwegian University of Science and Technology.[3] [4] [5] You can also follow the procedure on the Mayo Clinic website.[6]

 

4. What is VO2max?

VO2max is a commonly-used measure of aerobic fitness that basically shows the highest rate at which your body can supply oxygen to your contracting muscles.[7] The American Heart Association believes that this measure is so important it should be considered a “vital sign,” just like blood pressure, heart rate, temperature and respiration rate.[8]

 

5. If you stop exercising, how fast do you lose fitness and strength? And how fast can you regain it?

Unfortunately, maintaining fitness is truly a case of use it or lose it. How fast you lose it, of course, depends on how fit you were to start with, how old you are, how recently you stopped exercising and how long you had been exercising before you stopped.

For most of us, cardiovascular fitness starts to decline with just week or two of inactivity, while losing muscle mass and strength takes an extra week or so. Athletes and serious long-term exercisers tend to lose fitness more slowly than those who haven’t trained as long. [9] [10] [11]

In one classic study from the 1980s, volunteers trained hard for nine weeks then stopped for the next nine.[12] When training stopped, VO2max and the “anaerobic threshold” both dropped rapidly. (The anaerobic threshold, also called the lactate threshold, is the moment during exercise when lactic acid builds up faster than it can be cleared away.[13] [14])

In general, endurance (aerobic) conditioning can decline by as much as 25 percent after just three to four or five weeks of detraining.[15] [16] [17]

Some reports suggest that even just two weeks of detraining can lead to a significant decline in cardiovascular fitness, though once you get back into exercise, aerobic capacity rebounds faster than muscle strength.[18]  And some data suggests that adverse metabolic changes can occur with as few as 10 days of exercise cessation.[19] On the other hand, the enlargement of the heart from exercise declines fairly slowly – even complete bed rest only causes about one percent of heart muscle loss per week.[20]

As a basic rule of thumb, to maintain cardiovascular fitness gains you have to avoid breaks of longer than two to three weeks.[21] On the plus side, if you have to temporarily cut back on how often you exercise and how much, you can maintain some gains by not cutting back on how hard you train, that is, on intensity.[22]

Once you really lose fitness, it takes time –and patience – to regain it. After two to eight months of not exercising, you can lose all of your fitness gains.[23]  In fact, if you’ve really been inactive for a very long time, it can take a year to get into as good shape as you were in before you quit.[24] (Bed rest, as we’ve seen, is particularly dangerous, leading to rapid losses of fitness.)

As for muscle strength, as opposed to cardiovascular fitness, things are a bit rosier – you don’t lose the muscle mass you gain from resistance exercise as fast as you lose cardiovascular fitness. In part, that’s because strength training triggers formation of new nuclei in muscle cells.

In a 2017 analysis, researchers found that muscle strength can be maintained without training for as long as three to four weeks, after which it declines, though it can be rapidly restored when you start up again.[25] Other data supports this idea.[26] [27] [28] [29]  Some studies suggest that muscle mass gained from resistance training can last for months, even years.[30] (Prolonged detraining, of course, does lead to muscle loss.)

Even for people who do very serious strength training – “lifters” who have been doing resistance training for more than three years and who compete at the collegiate or professional level – maximum strength levels can also be maintained for up to three weeks without training, though after that, things do fall apart.[31]

With detraining, muscles do look smaller, but that’s because they contain less glycogen (a stored form of carbohydrates) and water.[32]

And it’s not just aerobic and strength gains that you lose when you stop exercising, but improvements in blood pressure, cholesterol and blood sugar levels, as well as muscle strength.[33]

In a Spanish study of obese people with metabolic syndrome who did four months of aerobic interval training,  just one month of no exercise led to the loss of many of these improvements, especially aerobic fitness.[34]

 

6. What is high-intensity interval training (HIIT)?

This kind of training alternates short bursts of very vigorous exercise with rest or slower activity, a pattern that is repeated multiple times. The idea is that you can get many of the benefits of a longer, continuous workout in much less time.[35] [36] [37]

The most famous test is the Wingate protocol, developed in the 1970s in Israel. It calls for a 30-second all-out effort, followed by four minutes of recovery. This pattern is repeated four to six times during one workout session. This amounts to three to four minutes of hard exercise per session with three sessions a week for two to six weeks.[38]

 

7. So is HIIT better than continuous training?

“Better” is a tricky word. At the very least, HIIT is highly effective and more time efficient, though, of course, any exercise is better than none at all. Before embarking on HIIT, check with your doctor if you are old, out of shape, sick or have hypertension or other cardiovascular problems.[39] (For more on HIIT, see Chapter 5.)

 

8. Can you be both fit and fat?

The debate is still raging, and obviously, both fitness and healthy body weight are important.[40] [41] [42] Some data suggest that fitness may be as important as weight, that is, that fitness strongly predicts mortality, regardless of body size. [43] [44] Put differently, some data show that higher levels of exercise can attenuate the mortality risk at all levels of adiposity. On the other hand, fatness or obesity does substantially reduce fitness,[45] and other data suggest that you can’t be both fit and fat.

Part of the problem comes in measuring fatness. In many studies, weight is gauged by BMI, body mass index. For the vast majority of people, BMI is a good measure of body fatness. But some people, such as weight lifters, can have a high BMI, suggesting they are overweight even when they are not. That’s because muscle weighs more than fat.

In a study of nearly 117,000 women followed for 24 years, the lowest mortality, not surprisingly, was in physically active, lean women. Higher levels of physical activity did reduce mortality risk but did not eliminate the high risk associated with obesity. And being thin did not counteract the increase in mortality risk from inactivity.[46]

A 2017 study of more than a half million Europeans followed for more than a decade found that there is no such thing as “fit but fat,” as the leader of that study told Fortune magazine.[47] This study found that being overweight raised the risk of coronary heart disease by up to 28 percent, even if a person was otherwise healthy.[48] The study adds “to a growing body of evidence that suggests that being ‘fat but fit’ is a myth,” the researchers from the Imperial College London noted in a statement.[49]

The biggest and most recent study, a British analysis of 3.5 million people published in 2017, also found that people who are obese are at an increased risk of heart failure and stroke even if they are “metabolically healthy,” that is, they don’t show obvious warning signs such as high blood pressure or diabetes.[50] [51] As long as these folks were obese, the study showed, they were at a modestly increased risk of stroke, a nearly 50 percent increased risk of coronary heart disease, and a nearly doubled risk of heart failure compared to those who were not obese and were in similar metabolic health.[52]  The leader of this study put it bluntly to the New York Times: “The bottom line is that metabolically healthy obesity doesn’t exist.” Or at least, is a state of affairs that can’t be maintained for long.[53]

 

9. Can you target exercise to control where your body loses fat?

Well, that’s not entirely clear. In general, exercise burns fat all over the body, but may not work as a “spot reduction” strategy.[54] [55] Some researchers believe that no matter how many sit-ups you do, you don’t actually change belly fat into muscle, and that, to lose fat, you have to expend more calories than you take in. But a 2015 study showed that weight training is particularly beneficial for reducing belly fat.[56] [57]

 

10. Is more exercise better than less for extending longevity?

Yes, to a point. A large study of 16,939 Harvard alumni showed that death rates declined steadily as exercise increased up to the point of expending 3,500 calories week, after which there is no reduction in mortality risk. Being physically active reduced mortality rates regardless of hypertension, smoking and extreme gains in body weight. By age 80, habitual exercisers were likely to have an extra one to two years of life, compared to sedentary men.[58]

A 2015 analysis of pooled data from six studies involving 661,137 men and women in the U.S. and Europe aged 21 to 98 showed that people who do one to two times the recommended minimum of moderate physical activity have a 32 percent lower mortality risk than those who do none. At two to three times the minimum recommendations, there is a 37 percent lower risk. The upper threshold for reducing mortality risk occurs at three to five times the activity recommendations.[59]

 

11.  Is there a level at which exercise is harmful if you’re healthy?

Well, the answer is mostly no. That study of 661,137 people found that even at 10 or more times the recommended exercise dose, there was no evidence of harm.[60] Other studies agree. On the other hand, a 2017 study did find that white men who exercised more than seven hours a week had a significantly higher risk of having plaque buildup in their arteries, though this does not necessarily translate into problems such as heart attacks.[61]

Ultrasound studies done at the end of marathons have shown potentially worrisome changes in both left and right ventricles of the heart, though these changes are usually transient.[62] [63] Certain biomarkers are also elevated right after a marathon in some runners. [64] [65] Atrial fibrillation (an irregular rhythm in the top chamber of the heart) is also five times more likely in middle-aged men who are endurance athletes.[66]

That said, a 2012 analysis of 10.9 million marathon runners showed a low overall risk of cardiac arrest and sudden death. When cardiac arrest does occur during long-distance running events, it does so rarely in half marathons (13.1 miles), but more often in full marathons (26.2 miles).[67]

 

12. Okay, but isn’t exercise dangerous for some people?

Yes, and obviously, if you’re in doubt, check with your doctor, especially if you have heart or lung problems, including hypertension. Also, if your blood counts are low and your immunity is compromised because of cancer or cancer treatment, it may be wise to wait to exercise until your counts are normal.

In a major review of the benefits and risks of exercise for people with one or more of 26 conditions, Scandinavian researchers generally found few contraindications for exercise.[68] Spanish scientists agreed.[69]

However, there are some caveats. For people with ischemic heart disease, in which blood flow to the heart is compromised, it may be wise not to do short, high intensity workouts. (See chapter 4.) For people with hypertension, weight training should focus on lighter weights; if your blood pressure is over 180/105, you should consider drug treatment to control blood pressure before exercising.

For people with Type 2 diabetes, overall, exercise is more a benefit than a risk. But you should postpone exercise if blood sugar levels are too high or too low; if you have hypertension or diabetic eye problems, including advanced retinopathy, it may be wise to avoid high intensity training. If you have nerve pain or foot problems, weight-bearing exercise can lead to ulcer and fracture.

If you have an acute exacerbation of asthma, take a temporary break from training. Ditto if you have an infection –wait until it’s gone. If you have cystic fibrosis as well as an infection, wait until you’re better.

If you have osteoarthritis with an acute joint inflammation, rest that joint until it’s improved, but exercise other joints. If you have osteoporosis, avoid exercises that increase your risk of falling. Don’t exercise a body part with a recent fracture. If you have rheumatoid arthritis, use low weights for strength training and be careful with your neck. If you have bone metastases from cancer, don’t lift heavy weights.

And then there’s the common sense stuff. Exercising an acutely injured body part is silly. As is doing things like biking on busy roads, especially without a helmet.

 

13. Should you exercise if you’re sick?

That depends on what you’re sick with and how sick you are.

Don’t exercise if you have a fever over 101 Fahrenheit. If you’ve got a cold and your symptoms are mostly above the neck (minor sore throat, runny nose, sneezing, etc.) it’s okay to exercise, moderately. If your symptoms are below the neck (chest congestion, stomach pain, etc.) wait until you’re better. If you do exercise, reduce the intensity and length of your workout. Don’t exercise if you have severe fatigue or widespread muscle aches.[70]

In general, regular aerobic exercise strengthens the immune system.[71] [72] (See Chapter 11.) But immunity can decrease slightly about 90 minutes after exercise, at least in elite athletes, then bounces up again. After a marathon, it can stay a bit low for 72 hours.[73] Wash your hands a lot if you work out in gyms during cold and flu season.

Light exercise if you’re mildly sick can even make you feel better, and can bring oxygenated blood to an area of infection, potentially helping to fight the infection.[74] But stay hydrated. And don’t do dumb things, like rock-climbing if you have vertigo or diving if your ears are plugged up!

 

14. Should you exercise while pregnant?

If you’re healthy and your pregnancy is normal, the American College of Obstetricians and Gynecologists and the Centers for Disease Control and Prevention recommend exercising for at least 30 minutes at moderate intensity for most, or all, days of the week.[75]

It used to be thought that exercise during pregnancy could increase the risk of preterm birth, perhaps by increasing levels of the stress hormone, norepinephrine. But an analysis of 9 studies involving more than 2,000 women found no significant difference in preterm births in women who exercised aerobically for 35 to 90 minutes three to four times a week during pregnancy compared to those who didn’t.[76] In fact, the women who exercised had a better chance of a vaginal delivery.

How long and hard you exercise depends on your previous activity levels. Exercise during pregnancy can reduce risk of gestational diabetes. Exercise, including low to moderate intensity weight training, can also help prevent excess weight gain, reduce back pain and ease constipation.[77] [78] [79] [80] [81]

Hormonal changes during pregnancy will make your joints more flexible, which can raise the risk of joint injury. Your balance may be off, too, because of your growing belly. Your need for oxygen increases as well.

Try to avoid contact sports in which you could get hit in the abdomen or activities like skiing that increase your risk of falling. “Hot” yoga is probably a bad idea, too, because you can overheat. Exercise over 6,000 feet is also unwise, unless you’re used to that altitude.

Also, don’t exercise without asking your doctor if you have certain types of heart or lung disease, cervical “insufficiency,” if you’re carrying multiple fetuses, or have severe anemia or preeclampsia (pregnancy-induced high blood pressure).

Exercise during pregnancy can reduce the risk of giving birth to a baby with serious heart defects, too.[82] In one experiment, mice allowed to run during pregnancy bore far fewer babies with heart defects than mice not allowed to run, even if the mothers-to-be were old. [83]

Exercise is also important after pregnancy.[84] Granted, time and sleep, are at a premium with a new baby, but exercise is key because it can help strengthen your abs and help prevent post-partum depression. You can start a few days after childbirth, though check with your doctor if you’ve had a cesarean delivery.

 

15. Does exercise help with menopausal symptoms?

It’s not clear. Some research finds that exercise does not help ease hot flashes, though it does help with sleep quality, insomnia and depression.[85]

Other research suggests that regular, moderate endurance exercise may reduce the frequency and intensity of hot flashes, though it’s not clear how.[86] [87] In a 2016 interventional study of 21 women with hot flashes who underwent a 16-week exercise training program, exercise was linked with fewer hot flashes.[88] But to get this effect, women had to build up to working out vigorously four or five times at week for 45 minutes each time. No one is sure how exercise might effect this, but it may be by improving the body’s heat regulation processes.[89]

  

16. Should men and women exercise differently?

By and large, no, but there are some caveats, and responses to exercise may differ. With weight training, for instance, men, with their higher levels of testosterone, tend to bulk up more than women.[90] But the difference is small.[91]

On the other hand, women, thanks to lots of estrogen, often have looser joints, which can raise the risk of joint damage with sudden twisting movements, as in basketball.[92]  Women’s knees are more vulnerable than men’s because the “Q-angle,” the angle between the hip and the knee, is greater because women’s hips are wider, which is great for childbearing, but not so good for landing from a jump and twisting. The extra torque in women’s knees can more easily shred the ACL (anterior cruciate ligament).

Men tend to have stronger tendons than women because they synthesize more collagen after exercise, making their tendons less susceptible to injury.[93]  Men also tend to have somewhat higher VO2max levels than women.[94]

A caveat, though. Some bodybuilding coaches, among them, Menno Henselmans, a business consultant turned fitness coach, contend that there are some differences in the way men and women should train, noting, among other things, that women may be less subject to fatigue and may be able to handle more training.[95] [96] [97]

 

17. Can you be allergic to exercise?

Yes. It’s rare, but it can be life-threatening, in which case it’s called exercise-induced anaphylaxis (EIA), a kind of shock. In some cases, the allergic reaction is triggered by a combination of certain foods followed by exercise, in which case it’s which called FDEIA, or food-dependent exercise-induced anaphylaxis.[98] Usually, the reaction happens during or right after exercise and can be manifested by hives, swelling, digestive problems, respiratory problems and other signs of shock. The most common food triggers are crustaceans and wheat flour. The cause appears to be changes in immune cells called mast cells, which release histamine.[99] Immediate treatment involves epinephrine and antihistamines, as well as airway maintenance and cardiovascular support. [100]

 

18. What causes muscle cramps?

Believe it or not, nobody is quite sure.[101]

Historically, lots of things have been postulated to contribute to exercise-induced muscle cramps, including overuse of a muscle, dehydration, holding a position for too long, nerve compression, inadequate blood supply to a muscle, imbalances of electrolytes such as magnesium, potassium and sodium and accumulation of lactic acid.[102] But science hasn’t supported much of this.[103]

Current thinking is that muscle cramps, generally thought to be harmless, occur because of hyperactivity of the nerve-muscle reflex arc, in other words, overuse of feedback communication involving nerves and muscles. Prolonged sitting or bad posture may predispose these reflexes toward malfunctioning. Stretching, for 15 to 30 seconds, may help get rid of the hyper-excitability of a cramping muscle. [104]

During a muscle cramp, the spinal cord may actually – mistakenly – tell the muscle to keep contracting. [105] Inadequate conditioning also contributes to cramps because untrained muscles are more prone to fatigue. Exercising in intense heat may also trigger cramps. Severe muscle cramps can be extremely painful; if cramps are severe and frequent, it makes sense to see a doctor.

 

19. Why do muscles feel sore after exercise?

It’s called DOMS, for delayed onset muscle soreness, and it usually strikes a day or two after a big workout.[106] The main culprit is eccentric exercise, that is, exercise that involves lengthening a muscle while it is contracting, like lowering your arm after a biceps curl. (Eccentric movement seems to trigger DOMS more than other motions.[107]) Technically, DOMS is a seen as a “Type I muscle strain injury.”

As we saw in Chapter 6, exercise triggers tiny tears in muscle tissue, which lead to painful inflammation and ultimately, repair and stronger muscles. There are other theories, too, including lactic acid buildup, muscle spasms, connective tissue damage and enzyme changes. But no single theory is likely to explain the entire process.[108]

Although some exercisers contend that free radicals (toxic forms of oxygen created during exercise) are to blame and that therefore antioxidants are the answer, that’s not true. (See Question 22.) Icing the affected area may not help, either.[109]

What may help is massage or the do-it-yourself version, using a foam-roller on the sore muscles. NSAIDS, non-steroidal anti-inflammatory drugs, can help. So can exercising non-sore parts of the body for a few days until DOMS disappears.

 

20. Does exercise change the kind of fat you have?

Though most of us assume all our body fat is pretty much the same, there are actually several different kinds. There’s subcutaneous fat that lies just under our skin and is basically harmless, and visceral fat, which covers our internal organs and in excess amounts can be metabolically harmful, in part because it secretes biochemical signals that increase chronic inflammation and insulin resistance.[110] [111]  Muscles can use fatty acids from fat as fuel.

But fat also comes in different colors. Brown fat is considered “good” because it can generate heat. In general, lean people have more brown fat than obese people, and kids have more brown fat than adults.

Exercise can transform white fat into brown fat, which is desirable in part because it is metabolically more active and burns more calories.[112] [113] [114] A hormone called irisin, produced in working muscles, can turn some white fat cells into brown.[115] People who exercise tend to have higher levels of irisin than sedentary folks. Exercise may also stimulate production of proteins that lead to growth of more blood vessels.[116]

 

21. Does exercise alone help you lose weight? 

Yes, but it takes an awful lot of exercise. Olympic swim champ Michael Phelps, for instance, consumed 12,000 calories a day during peak training, but as he put it himself, all he did was “swim, eat and sleep.” [117]

But most of us ordinary mortals don’t exercise that much. And, as we saw in the obesity section of Chapter 4, the math is against you. In theory, since weight gain results from too much food and too little exercise, you could lose weight just by increasing exercise and keeping food intake constant. But for most of us, that doesn’t work because we tend to underestimate the calories we ingest in food and overestimate how many calories we burn in exercise.[118] A 160-pound person walking at a 20-minute a mile pace burns just 255 calories in an hour – the calories in one small muffin! [119] [120]

Just by itself, without dietary changes, exercise usually won’t help you lose weight.[121] [122] In fact, some data show that Americans have actually been exercising more in recent years, even as the obesity epidemic has worsened.[123]  Diet alone even edged out diet-plus-exercise in one study of weight loss.[124] Long term, combining exercise with diet seems to work best.[125] [126]

 

22. How does exercise affect appetite?

Well, it’s complicated.[127] [128] [129] Most research shows that exercise suppresses appetite, at least for a couple of hours. But not in everybody. Go figure. 

Exercise, particularly strenuous exercise, can act as an appetite suppressant by lowering levels of the hormone ghrelin, an appetite stimulant often called the “hunger hormone,” and boosting levels of blood lactate and blood sugar, which lessen the need to eat.[130] [131] [132] [133]

One study, for instance, found that vigorous aerobic exercise – 60 minutes on a treadmill – lowered levels of ghrelin and also raised levels of peptide YY, an appetite suppressor, although resistance exercise had a more mixed effect. The hunger-suppressing effect of vigorous exercise lasted about two hours.[134] In a subsequent study, the same researchers confirmed that exercise intensity and to a lesser extent, duration, were linked to lower ghrelin levels.[135] Exercise can also increase levels of leptin, according to a Spanish research review.[136] Leptin is an appetite suppressor.[137]

But exercise can sometimes stimulate appetite. While appetite does go down immediately after exercise, as body temperature cools down again, appetite may increase.[138]

Bottom line? It really is complex. But overall, it’s easier to regulate appetite if you’re expending a lot of energy, one of the big benefits of exercise. In essence, exercise makes for better “coupling” of energy intake and energy expenditure. Besides, when you’re sedentary it’s harder to control appetite.[139]

 

23. Is caffeine a performance enhancer?

Yes. Caffeine can act as a performance enhancer (or “ergogenic aid”) during exercise and competitions. Caffeine doesn’t actually boost maximum oxygen capacity, but can improve speed and power during races. Interestingly, this effect holds true in events lasting 60 seconds to those lasting two hours. There’s no evidence that caffeine leads to dehydration or ion imbalances. The bad news, at least in one study, is that drinking coffee may not work as well as “doping” with pure caffeine.[140]

Moderate to high doses of caffeine (5 to 13 milligrams per kilogram of body weight) has profound effects on exercise. Low doses (less than or equal to 3 mg per kg of body weight) don’t change the whole-body response to exercise, but can improve vigilance, alertness, mood and cognitive processing during exercise. The effects of caffeine probably stem from changes in the central nervous system.[141]

Caffeine may also help keep dopamine levels high in the brain areas needed for concentration and reduce the perception of pain and effort during exercise, potentially help maintain effort longer.[142]

 

24. Do antioxidant vitamins offset the benefits of exercise?

Well, it’s fair to say that, at the very least, antioxidant vitamins don’t enhance the benefits of exercise.[143] Exercise does create free radicals, toxic forms of oxygen (also known as unpaired electrons). And free radicals do cause “oxidative stress.” But exercise also triggers formation in the body of antioxidants, which can counteract the effect of some free radicals.[144] [145] If you take supplementary vitamin C or E, for instance, you may wind up with fewer of the enzymes that trigger what you want – an increase in mitochondria (the energy factories) in muscle cells.[146] [147] In other words, antioxidant supplementation may actually retard the expected increase in fitness and strength from exercise. This seems to hold true whether exercise is aerobic or resistance training.

To be sure, antioxidant supplements, which have been vigorously promoted by the supplement industry, have long been popular among athletes eager to improve performance. But the current thinking is that free radicals are not as “bad” as once thought, nor antioxidant supplements as “good.” In fact, an imbalance – too many antioxidants compared to free radicals – can result in its own problem, dubbed “antioxidant-induced stress,” in part because antioxidants themselves become highly reactive after they donate their electrons to free radicals.[148]Antioxidants that occur naturally in food appear to be much safer than large doses of supplements.[149]

 

25. Is it safe to exercise if you take beta-blockers?

Beta-blockers are cardiac medications that block the effects of adrenaline, the “fight-or-flight” hormone. They are used to lower heart rate and blood pressure. In general, it’s fine to exercise while on beta-blockers but don’t push it in an attempt to get your heart rate up to the level you attained without beta-blockers.[150] [151]

Check with your doctor to find out what target heart rate you should aim for while on these medications. If you can’t talk while exercising, back off a bit. There are also other drugs that your doctor might consider switching to.

 

26. Are “accelerometers” and other “activity trackers” accurate?

Somewhat. These devices are a great way to guard against deluding yourself about how many steps you actually get per day. Because they are so much better than just asking people to remember how much they exercised on a given day, accelerometers are the coming wave of exercise research.[152] [153]

They’re also great when exercise researchers use them (notably, the research-grade devices such as ActiGraph GT3X+) to track what you do, as opposed to what you say you think you did.

But accelerometers and other movement sensors such as Fitbit, JawBone, Nike Fuel, Garmin, Samsung GearFit2, TomTom, Apple Watch, while pretty good at counting steps, are not so good at calculating caloric expenditure and heart-rate, especially during higher intensity workouts.[154]

Research studies have shown mixed results. In one court case against Fitbit, a non-peer-reviewed study commissioned by the plaintiffs and vigorously denounced by Fitbit, found that the device was highly inaccurate during intense exercise.[155] (For what it’s worth, I wear a Fitbit and found it very inaccurate for heart-rate with vigorous workouts, but better at for step-counting, except on elliptical machines.)

In another study of different Fitbit devices and Jawbone UP24, the devices were good at counting calories for sedentary activity, but overestimated energy expenditure during exercise, including walking. In this study, one device, the Fitbit Flex, was more accurate than the others at judging energy expenditure and steps.[156]

On the other hand, a Stanford University School of Medicine study of seven wristband activity trackers came to completely different conclusions: That the six of the devices were fairly accurate for heart-rate but none of the seven was accurate for calories burned.[157] [158]

 

27. Can exercise improve vision?

 Surprisingly, yes, especially aging-related vision problems such as AMD (wet age-related macular degeneration), cataracts and glaucoma.[159] [160]

Among other things, exercise, as we saw in Chapters 8 and 9, triggers production of BDNF (brain-derived neurotrophic factor), which may boost the number of brain cells, including cells in the retina. (The retina is technically part of the brain.)  Some vision problems stem from high blood pressure and cholesterol, which can be lowered via exercise. Exercise also helps control Type 2 diabetes, which can damage the retina.

One 2013 study found that moderate walking and vigorous running are both linked with a lower risk of cataracts.[161] A massive 2015 Swedish study of 52,660 people followed for an average of 12 years found that those who exercised the most had a 13 percent reduced risk of cataracts compared to people who exercised the least.[162]

As for BDNF, dubbed “Miracle Gro” for the brain, exercise may do as much for the eyes as for the rest of the brain. In a clever 2009 study of more than 40,000 middle-aged distance runners, researchers found that the runners who logged the most miles were the least likely to get macular degeneration, regardless of weight, cardiorespiratory fitness and smoking.[163]

In an interventional study in mice, researchers from Emory University assigned half of a group of mice to a sedentary lifestyle and allowed the others to run on little treadmills for an hour a day.[164] After two weeks, half of the mice in each group were exposed to very bright light for a few hours, a way of experimentally inducing retinal degeneration. All the mice then went back for two weeks to whatever condition they were in before, either sitting or running. Then the scientists looked at all the animals’ retinas – the mice that didn’t exercise had lost 75 percent of their retinal neurons and their vision was failing. The mice that had exercised were able to maintain twice as many neurons as the unexercised mice, despite exposure to that bright light.

In a separate experiment, the researchers took another batch of mice and had half exercise and half not for two weeks, then measured the levels of BDNF in their bloodstream and in their eyes. The exercising mice, as expected, had more BDNF. Then, the researchers injected still other mice with a substance that blocks BDNF before they exercised and were exposed to the bright light. Bingo! Without BDNF, these animals’ retinas were not protected by exercise.

But there is a potential shadow over all this positive news. A 2017 Korean study that tracked 211,960 middle-aged and older men and women found that those who exercised vigorously five or more days a week had a 54 percent increased risk of macular degeneration. But, as the authors themselves note, there is no strong biological rationale for this finding, and no association was found for women.[165] So this has to be taken with a large grain of salt.

 

28. Does exercise benefit the skin?

Yes.

At a minimum, improved circulation is just as good for the skin as for every other organ in the body, bringing freshly oxygenated blood to skin cells and taking away cellular waste products. Since exercise can also ease stress, it can help reduce stress-related skin problems such as acne and eczema too.[166]

But recent research suggests exercise may even reverse skin aging. As we hit midlife, the layers of the skin begin to change, most notably the outer layer of the skin called the stratum corneum, which thickens, while a deeper layer of the skin, the dermis, gets thinner, explains New York Times fitness columnist Gretchen Reynolds.[167]

It’s been known for a number of years now that exercise is good for mitochondria, the energy factories inside cells. (See Chapter 5). In fact, in 2011, McMaster University researchers showed that, in mice bred to age prematurely, exercise restores sagging mitochondria and prolongs life.[168]

With that in mind, the McMaster team then set out to see what effect, if any, exercise might have on the aging of human skin.[169] In a meticulous 2015 study, they showed that endurance exercise does indeed slow aging-induced changes in the skin. It does so by increasing levels of hormones called myokines, which are made in contracting muscle cells. Specifically, the researchers found that a myokine called IL-15 triggers the exercise-associated improvements in the skin of older people. Indeed, they found higher levels of IL-15 in the skin of exercisers compared to non-exercisers

 

29. Does exercise affect the teeth?

Well, maybe, and perhaps not for the better. But don’t let that stop you from exercising.

The data is preliminary, and potentially flawed. Working out long and hard may temporarily change saliva in a more alkaline direction, which could interfere with a protein in saliva whose job is to prevent tooth decay.[170]

A 2013 study in the British Journal of Sports Medicine looked at 278 athletes participating in the London 2012 Olympic Games.[171]Their oral health was remarkably poor, despite their stupendous overall fitness. In fact, a majority had high levels of tooth decay and some also had gum disease and erosion of tooth enamel. It wasn’t clear why these ultra-healthy folks had such bad dental health, but nearly half had not had a dental exam or hygiene care in the previous year. The athletes studied were not a random sample, but were recruited from a free dental care clinic, and many of the athletes were from Africa, where dental care can be less available.

In 2015, German researchers compared the teeth and saliva of 35 competitive triathletes and 35 healthy people who were not athletes.[172] Fifteen of the athletes also volunteered for an experiment in which they did an increasingly-strenuous run during which their saliva was collected several times. Overall, the athletes showed more erosion of tooth enamel than the controls. They had more cavities, too – and the more hours they exercised, the more cavities they had.

When both the athletes, who trained hard (nine hours a week on average) and the non-exercisers were at rest, their saliva was chemically similar. But during the running part of the experiment, runners produced less and less saliva (even if they were hydrated) and their saliva became more alkaline, a process that can lead to the buildup of plaque.

Surprisingly, the researchers found no direct link between sports drinks and nutrition and dental decay. But stay tuned on this one – it may be that athletes drink more sugary drinks than reported.

 

30. Why should you “surprise” your muscles?

Believe it or not, your muscles get “bored” if you do the same workout over and over. After 6 to 8 weeks of the same routine, your neuromuscular system adapts and goes on cruise control.[173] You’ll still build muscle, but not as much as with a tougher workout. To prevent plateauing, you can increase the intensity of training and/or substitute new exercises for old ones every couple of months.

Many factors contribute to the beneficial effects of varying your exercise routine. At the molecular level, the body doesn’t perceive easy exercise as a stress. (In this case, “stress” is a good thing.) But when exercise is hard enough, the sympathetic nervous system pumps out catecholamines (the “fight or flight” hormones, adrenaline and norepinephrine). These hormones act on a protein called CRTC2, which in turn improves the body’s ability to use sugar and fatty acids, ultimately yielding bigger, stronger muscles.[174] [175] If there’s insufficient exercise stress, some researchers say, this catecholamine cascade never gets cranked up. In other words, there’s truth in the “no pain, no gain” theory.

 

31. Does exercise affect circadian rhythms? Does it help remedy jet lag?

Yes, and yes.

Circadian rhythms, which exist in animals, plants and some microbes, are physical, mental and behavioral changes that follow a daily cycle. In fact, many of our organs – the heart, liver, brain – even have their own distinct circadian rhythms.[176] [177]

A hot topic these days, “circadian” (which means “about daily,” or roughly, 24-hour) rhythms, were the subject of a 2017 Nobel Prize. These biological patterns are triggered when light hits a tiny part of the brain called the supra-chiasmatic nucleus. (During our evolutionary history, the light that controlled this was sunlight; now, artificial light, especially in the evening, often disrupts these natural rhythms.)

These natural rhythms have powerful effects on sleep, alertness, hunger, activity and many other functions. Indeed, one study showed that the risk of having a car accident goes up 8 percent in the week after the spring shift for daylight saving time, which causes people to lose one hour of sleep. In the fall, when the shift provides an extra hour of sleep, there’s a similar reduction in accidents.[178]

Young people tend to move around a lot during the day and not so much at night, but this pattern becomes somewhat less regulated as we age.[179] (Older people tend to move less during the day and be restless at night.)

But, crucially, exercise, by pumping out important biochemicals that act on various organs, can help keep circadian rhythms synced properly, while lack of exercise can do the opposite. [180] [181] Exercise can even restore an out-of-sync circadian rhythm to a more normal, healthy one.[182]

In studies in mice, carefully scheduled exercise was able to re-set dysregulated circadian rhythms, in part by changing gene expression in the suprachiasmatic nucleus in the brain.[183] In other studies, exercise seems able to affect circadian rhythms, especially those linked to activity and moving around, and lack of exercise can disrupt these rhythms. Exercise can shift the molecular circadian clock in muscle tissue, too.[184]

As for jet lag, scientists are trying to see if exercise, as well as exposure to sunlight, in the new time zone helps re-set the circadian clock. In one study, researchers simulated jet lag in hamsters by altering the normal day-night lighting in their cages, then allowed some animals to run on little wheels. The animals allowed to run adjusted to “jet lag” much faster than non-exercising animals.[185] Humans, too, can benefit from exercising, especially exercising outdoors, to reduce jet lag.[186] Some researchers suggest exercising in the new time zone at the same time of day when you would work out at home.[187]

 

32. Is there an optimal time of day to exercise?

The snarky answer is, whenever you can fit it in. The scientific answer, alas, is not much better because the data are mixed.[188] Some studies say morning is best, in part because you can do it before your day gets away from you.[189] Others say late afternoon is best, perhaps because that’s when body temperature peaks and perceived exertion (how hard you feel you are working) is lowest.[190] [191] [192] This may be especially true for non-aerobic exercise.

 

33. Does exercise affect sleep?

Yes. Regular, aerobic exercise during the day can help relieve stress and in other ways help with sleep, though it may take four months for the benefits – including falling asleep more rapidly and staying asleep longer – to solidify.[193] [194] [195] Interestingly, in the short run, a good night’s sleep may have a stronger effect on exercising well the next day than the reverse, at least in people with diagnosed insomnia.[196]

The mechanisms are not totally clear, but exercise does help keep circadian rhythms humming along nicely. And it temporarily increases body temperature, with the subsequent drop in temperature helping to promote sleep.

That said, research suggests avoiding exercise within three hours of bedtime lest it rev you up and interfere with falling asleep.[197] Among other things, the body needs to cool down in the late evening, which sets the stage for sleep. But a small study found that late-night exercise does not seem to disturb subject sleep quality, though it was linked to a faster heartbeat during the first three hours of sleep.[198]

 

34. Is exercise addictive?

To some extent, in some people, but it’s tough to tell exercise addicts from people who just like to exercise a lot. Exercise addiction is not recognized in the DSM-5, the Diagnostic and Statistical Manual of Mental Disorders, a  handbook of psychiatric disorders.[199]

Exercise may be viewed as addictive if you prioritize it above all else, potentially damaging your work and personal life, in other words, when exercise becomes life’s organizing principle. Some researchers estimate the prevalence of exercise addiction to be about 3 percent of the general population.[200]

The psychological effects of exercise, as we’ve seen earlier in this book, can be powerful, so powerful in fact that “exercise may be considered as a psychoactive drug,” write Spanish researchers.[201] This may pose a risk for extreme exercisers, such as ultra-marathoners, body builders and sports science students, they add. Exercise does trigger release of important biochemicals, including endorphins, dopamine, BDNF and stress hormones. Exercise also boosts endocannabinoids, marijuana-like substances made in the body.[202] (See Chapter 9.) Whether this triggers a genuine physical addiction is not fully clear. In addition, exercise may reduce anxiety by raising body temperature.[203]

To qualify as a genuine “behavioral addiction,” California psychologists argue that several features must be present.[204]

These include: tolerance (you need more and more exercise to get the desired effect); withdrawal (skipping exercise triggers negative emotions like anxiety and irritability); lack of control (unsuccessful attempts to cut back on exercise); intention effects (inability to stick to your normal routine because exercise gets in the way); time (large amounts of time go toward exercising and planning and recovering from it); reduction in other activities (like family, work or socializing); continuance (keeping up exercise despite knowing it is contributing to physical or psychological problems).

On the plus side, it’s possible that exercise may help combat drug addiction. A small 2010 study in rats showed that running on a little exercise wheel may help reduce relapses with cocaine addiction.[205]

 

35. Is running the best exercise? 

Maybe. Running is efficient, in the sense that you expend more calories per unit of time spent than walking, biking or many other activities.[206] [207] Compared to non-runners, runners have a reduced risk of dying early from any cause by between 25 and 40 percent, regardless of drinking, smoking or being overweight. An hour of running can increase life expectancy by about 7 hours, making it a better way to prolong life than walking, cycling or swimming, although, as we’ve consistently noted, any exercise is far better than none.[208] [209] Running achieves this mainly by reducing the risks of heart disease and cancer.

 

36. Endurance vs. Resistance – Do you have to choose?

 Yes, if you’re an elite athlete dedicated to a specific event, such as weight lifting or marathon running. No, if you’re just trying to stay as fit and strong as possible. In fact, except for truly elite athletes, the ideal path is a combination, to both ward off sarcopenia and to maintain overall fitness.[210] [211]

Doing both makes sense, evolutionarily. After all, we evolved both to be fit enough to escape predators and hunt food, and to be strong enough to carry animal carcasses back to the fire.

On the other hand, you can’t be great at both. It is “hardly surprising that simultaneously training for both endurance and strength results in a compromised adaptation compared with training for either exercise alone, a phenomenon known as the ‘interference effect,” writes Australian researcher John A. Hawley.[212]

Then again, consider a 1980 study that compared strength and endurance training. Researchers divided participants into three groups: one did endurance training only, one did strength training only and one did both.[213] Only the folks whose workouts included endurance training showed increases in VO2 max. Only the strength training group showed improvement in leg strength.

Research in rats seems to verify the idea that there is a “master switch” that, depending on whether the stimulus sends a muscle along either the mitochondrial or the hypertrophy pathway. (See Chapters 5 and 6.)[214] Whether such a master switch occurs in humans is not so clear.

In one 2006 study, researchers used highly trained endurance athletes and highly trained resistance athletes and had both groups do a tough bout of exercise in their own expertise. They then “crossed over” to the other type of exercise– and did just fine, suggesting considerable “response plasticity.”[215]

In his excellent 2011 book,  “Which Comes First, Cardio or Weights?” Canadian physicist and journalist Alex Hutchinson, writes, “You can’t fulfill your ultimate potential as both a weight lifter and a marathoner at the same time.”[216]  But for most of us, he says, you can mix it up, that is, do both.

Bottom line? Unless you’re an elite athlete, “You don’t have to choose,” says Mark Tarnopolsky, a mitochondrial disease specialist at McMaster University.[217] “My conclusion is to combine the two, resistance and endurance, either on the same day or on alternate days.”

 

37. Does exercise offset the cancer and heart disease mortality risks of drinking?

Yes, according to a study of more than 36,000 men and women aged 40 and over.[218] So long as a person meets the recommended physical activity guidelines, exercise can offset some of the risks of cancer and all-cause mortality that are associated with drinking. But you can’t rely on exercise to cancel out the effects of heavy drinking.[219]

 

38. If you do all this exercise, will you live forever?

No, but you’ll die buff!

 

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