Created by CK-12 Foundation/Adapted by Christine Miller
Stroller Moms
These moms (Figure 12.5.1) are setting a great example for their children by engaging in physical exercise. Adopting a habit of regular physical exercise is one of the most important ways to maintain fitness and good health. From higher self-esteem to a healthier heart, physical exercise can have a positive effect on virtually all aspects of health, including physical, mental, and emotional health.
What Is Physical Exercise?
Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. We generally think of physical exercise as activities that are undertaken for the main purpose of improving physical fitness and health. However, physical activities that are undertaken for other purposes may also count as physical exercise. Scrubbing a floor, raking a lawn, or playing active games with young children or a pet are all activities that can have fitness and health benefits, even though they generally are not done mainly for this purpose.
How much physical exercise should people get? In the Canada, both the Canadian Food Guide and the Canadian Society for Exercise Physiology recommend that every child and adult who is able should participate in moderate exercise for a minimum of 60 minutes a day. This might include walking, swimming, and/or household or yard work.
Types of Physical Exercise
Physical exercise can be classified into three types, depending on the effects it has on the body: aerobic exercise, anaerobic exercise, and flexibility exercise. Many specific examples of physical exercise (including playing soccer and rock climbing) can be classified as more than one type.
Aerobic Exercise
Aerobic exerciseis any physical activity in which muscles are used at well below their maximum contraction strength, but for long periods of time. Aerobic exercise uses a relatively high percentage of slow-twitch muscle fibres that consume a large amount of oxygen. The main goal of aerobic exercise is to increase cardiovascular endurance, although it can have many other benefits, including muscle toning. Examples of aerobic exercise include cycling, swimming, brisk walking, jumping rope, rowing, hiking, tennis, and kayaking as shown in Figure 12.5.2 .
Anaerobic Exercise
Anaerobic exercise is any physical activity in which muscles are used at close to their maximum contraction strength, but for relatively short periods of time. Anaerobic exercise uses a relatively high percentage of fast-twitch muscle fibres that consume a small amount of oxygen. Goals of anaerobic exercise include building and strengthening muscles, as well as improving bone strength, balance, and coordination. Examples of anaerobic exercise include push-ups, lunges, sprinting, interval training, resistance training, and weight training (such as biceps curls with a dumbbell, as pictured in Figure 12.5.3).
Flexibility Exercise
Flexibility exercise is any physical activity that stretches and lengthens muscles. Goals of flexibility exercise include increasing joint flexibility, keeping muscles limber, and improving the range of motion, all of which can reduce the risk of injury. Examples of flexibility exercise include stretching, yoga (as in Figure 12.5.4), and tai chi.
Health Benefits of Physical Exercise
Many studies have shown that physical exercise is positively correlated with a diversity of health benefits. Some of these benefits include maintaining physical fitness, losing weight and maintaining a healthy weight, regulating digestive health, building and maintaining healthy bone density, increasing muscle strength, improving joint mobility, strengthening the immune system, boosting cognitive ability, and promoting psychological well-being. Some studies have also found a significant positive correlation between exercise and both quality of life and life expectancy. People who participate in moderate to high levels of physical activity have been shown to have lower mortality rates than people of the same ages who are not physically active and daily exercise has been shown to increase life expectancy up to an average of five years.
The underlying physiological mechanisms explaining why exercise has these positive health benefits are not completely understood. However, developing research suggests that many of the benefits of exercise may come about because of the role of skeletal muscles as endocrine organs. Contracting muscles release hormones called myokines, which promote tissue repair and the growth of new tissue. Myokines also have anti-inflammatory effects, which, in turn, reduce the risk of developing inflammatory diseases. Exercise also reduces levels of cortisol, the adrenal cortex stress hormone that may cause many health problems — both physical and mental — at sustained high levels.
Cardiovascular Benefits of Physical Exercise
The beneficial effects of exercise on the cardiovascular system are well documented. Physical inactivity has been identified as a risk factor for the development of coronary artery disease. There is also a direct correlation between physical inactivity and cardiovascular disease mortality. Physical exercise, in contrast, has been demonstrated to reduce several risk factors for cardiovascular disease, including hypertension (high blood pressure), “bad” cholesterol (low-density lipoproteins), high total cholesterol, and excess body weight. Physical exercise has also been shown to increase “good” cholesterol (high-density lipoproteins), insulin sensitivity, the mechanical efficiency of the heart, and exercise tolerance, which is the ability to perform physical activity without undue stress and fatigue.
Cognitive Benefits of Physical Exercise
Physical exercise has been shown to help protect people from developing neurodegenerative disorders, such as dementia. A 30-year study of almost 2,400 men found that those who exercised regularly had a 59 per cent reduction in dementia when compared with those who did not exercise. Similarly, a review of cognitive enrichment therapies for the elderly found that physical activity — in particular, aerobic exercise — can enhance the cognitive function of older adults. Anecdotal evidence suggests that frequent exercise may even help reverse alcohol-induced brain damage. There are several possible reasons why exercise is so beneficial for the brain. Physical exercise:
- Increases blood flow and oxygen availability to the brain.
- Increases growth factors that promote new brain cells and new neuronal pathways in the brain.
- Increases levels of neurotransmitters (such as serotonin), which increase memory retention, information processing, and cognition.
Mental Health Benefits of Physical Exercise
Numerous studies suggest that regular aerobic exercise works as well as pharmaceutical antidepressants in treating mild-to-moderate depression. A possible reason for this effect is that exercise increases the biosynthesis of at least three neurochemicals that may act as euphoriants. The euphoric effect of exercise is well known. Distance runners may refer to it as “runner’s high,” and people who participate in crew (as in Figure 12.5.5) may refer to it as “rower’s high.” Because of these effects, health care providers often promote the use of aerobic exercise as a treatment for depression.
Additional mental health benefits of physical exercise include reducing stress, improving body image, and promoting positive self-esteem. Conversely, there is evidence to suggest that being sedentary is associated with increased risk of anxiety.
Sleep Benefits of Physical Exercise
A recent review of published scientific research suggests that exercise generally improves sleep for most people, and helps sleep disorders, such as insomnia. In fact, exercise is the most recommended alternative to sleeping pills for people with insomnia. For sleep benefits, the optimum time to exercise may be four to eight hours before bedtime, although exercise at any time of day seems to be beneficial. The only possible exception is heavy exercise undertaken shortly before bedtime, which may actually interfere with sleep.
Other Benefits of Physical Exercise
Some studies suggest that physical activity may benefit the immune system. For example, moderate exercise has been found to be associated with a decreased incidence of upper respiratory tract infections. Evidence from many studies has found a correlation between physical exercise and reduced death rates from cancer, specifically breast cancer and colon cancer. Physical exercise has also been shown to reduce the risk of type 2 diabetes and obesity.
Variation in Responses to Physical Exercise
Not everyone benefits equally from physical exercise. When participating in aerobic exercise, most people will have a moderate increase in their endurance, but some people will as much as double their endurance. Some people, on the other hand, will show little or no increase in endurance from aerobic exercise. Genetic differences in slow-twitch and fast-twitch skeletal muscle fibres may play a role in these different results. People with more slow-twitch fibres may be able to develop greater endurance, because these muscle fibres have more capillaries, mitochondria, and myoglobin than fast-twitch fibres. As a result, slow-twitch fibres can carry more oxygen and sustain aerobic activity for a longer period of time than fast-twitch fibres. Studies show that endurance athletes (like the marathoner pictured in Figure 12.5.6) generally do tend to have a higher proportion of slow-twitch fibres than other people.
There is also great variation in individual responses to muscle building as a result of anaerobic exercise. Some people have a much greater capacity to increase muscle size and strength, whereas other people never develop large muscles, no matter how much they exercise them. People who have more fast-twitch than slow-twitch muscle fibres may be able to develop bigger, stronger muscles, because fast-twitch muscle fibres contribute more to muscle strength and have greater potential to increase in mass. Evidence suggests that athletes who excel at power activities (such as throwing and jumping) tend to have a higher proportion of fast-twitch fibres than do endurance athletes.
Can You “Overdose” on Physical Exercise?
Is it possible to exercise too much? Can too much exercise be harmful? Evidence suggests that some adverse effects may occur if exercise is extremely intense and the body is not given proper rest between exercise sessions. Athletes who train for multiple marathons have been shown to develop scarring of the heart and heart rhythm abnormalities. Doing too much exercise without prior conditioning also increases the risk of injuries to muscles and joints. Damage to muscles due to overexertion is often seen in new military recruits (see Figure 12.5.7). Too much exercise in females may cause amenorrhea, which is a cessation of menstrual periods. When this occurs, it generally indicates that a woman is pushing her body too hard.
Many people develop delayed onset muscle soreness (DOMS), which is pain or discomfort in muscles that is felt one to three days after exercising, and generally subsides two or three days later. DOMS was once thought to be caused by the buildup of lactic acid in the muscles. Lactic acid is a product of anaerobic respiration in muscle tissues. However, lactic acid disperses fairly rapidly, so it is unlikely to explain pain experienced several days after exercise. The current theory is that DOMS is caused by tiny tears in muscle fibres, which occur when muscles are used at too high a level of intensity.
Feature: My Human Body
Most people know that exercise is important for good health, and it’s easy to find endless advice about exercise programs and fitness plans. What is not so easy to find is the motivation to start exercising — and to stick with it. This is the main reason why so many people fail to get regular exercise. Practical concerns like a busy schedule and bad weather can certainly make exercising more of a challenge, but the biggest barriers to adopting a regular exercise routine are mental. If you want to exercise but find yourself making excuses or getting discouraged and giving up, here are some tips that may help you get started and stay moving:
- Avoid an all-or-nothing point of view. Don’t think you need to spend hours sweating at the gym or training for a marathon to get healthy. Even a little bit of exercise is better than nothing at all. Start out with ten or 15 minutes of moderate activity each day. Taking a walk around your neighborhood is a great way to begin! From there, gradually increase the amount of time until you are exercising to at least 30 minutes a day, five days a week. Make it a routine.
- Be kind to yourself, and reinforce positive behaviors with rewards. Don’t be down on yourself because you are overweight or out of shape. Don’t beat yourself up because of a supposed lack of willpower. Instead, look at any past failures as opportunities to learn and do better. When you do achieve even small exercise goals, treat yourself to something special. Did you just complete your first workout? Reward yourself with a relaxing bath or other treat.
- Don’t make excuses for not exercising. Common complaints include being too busy or tired or not athletic enough. Such excuses are not valid reasons to avoid exercising, and they will sabotage any plans to improve your fitness. If you can’t find a 30-minute period to work out, try to find ten minutes, three times a day. If you’re feeling tired, know that exercise can actually reduce fatigue and boost your energy level. If you feel clumsy and uncoordinated, remind yourself that you don’t need to be athletic to take a walk or engage in vigorous house or yard work.
- Find an activity that you truly enjoy doing. Don’t think you have to lift weights or run on a treadmill to exercise your muscles. If you find such activities boring or unpleasant, you won’t stick with them. Any activity that increases your heart rate and uses large muscles can provide a workout, especially if you’re not in the habit of exercising, so find something you like to do. Do you like to dance? Put on some music and dance up a sweat! Do you enjoy gardening? Get out in the yard and dig up some dirt! Still not interested? Try an activity-based video game, such as Wii or Kinect. You may find it so much fun that it doesn’t seem like exercise until you realize you’ve worked up a sweat.
- Make yourself accountable. Tell friends and family members that you’re going to start exercising. You’ll be letting them — as well as yourself — down if you don’t follow through. Some people find that keeping an exercise log to track their progress is a good way to be accountable and stick to an exercise program. Perhaps the best way to keep at it is to find an exercise partner. If you’ve got someone waiting to exercise with you, you will be less likely to make excuses for not exercising.
- Add more physical activity to your daily life. You don’t need to follow a structured exercise program to increase your activity level. Do your house or yard work briskly for a workout. Park your car further than necessary from work or the mall, and walk the extra distance. If you live close enough, leave the car at home and walk to and from your destination. Rather than taking elevators or escalators, walk up and down stairs. When you take breaks at work, take a walk instead of sitting. Every time a commercial comes on while you’re watching TV, take a quick exercise break — run in place or do some curls with hand weights.
12.5 Summary
- Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health. Activities such as household chores may count as physical exercise, even if they are not done for their health benefits. Current recommendations for adults are 30 minutes a day of moderate exercise.
- Aerobic exercise is any physical activity that uses muscles at less than their maximum contraction strength, but for long periods of time. This type of exercise uses a relatively high percentage of slow-twitch muscle fibres that consume large amounts of oxygen. Aerobic exercises increase cardiovascular endurance and include cycling and brisk walking.
- Anaerobic exercise is any physical activity that uses muscles at close to their maximum contraction strength, but for short periods of time. This type of exercise uses a relatively high percentage of fast-twitch muscle fibres that consume small amounts of oxygen. Anaerobic exercises increase muscle and bone mass and strength, and they include push-ups and sprinting.
- Flexibility exercise is any physical activity that stretches and lengthens muscles, thereby improving range of motion and reducing risk of injury. Examples include stretching and yoga.
- Many studies have shown that physical exercise is positively correlated with a diversity of physical, mental, and emotional health benefits. Physical exercise also increases quality of life and life expectancy.
- Many of the benefits of exercise may come about because contracting muscles release hormones called myokines, which promote tissue repair and growth and have anti-inflammatory effects.
- Physical exercise can reduce risk factors for cardiovascular disease, including hypertension and excess body weight. Physical exercise can also increase factors associated with cardiovascular health, such as mechanical efficiency of the heart.
- Physical exercise has been shown to offer protection from dementia and other cognitive problems, perhaps because it increases blood flow or neurotransmitters in the brain, among other potential effects.
- Numerous studies suggest that regular aerobic exercise works as well as pharmaceutical antidepressants in treating mild-to-moderate depression, possibly because it increases synthesis of natural euphoriants in the brain.
- Research shows that physical exercise generally improves sleep for most people and helps sleep disorders, such as insomnia. Other health benefits of physical exercise include better immune system function and reduced risk of type 2 diabetes and obesity.
- There is great variation in individual responses to exercise, partly due to genetic differences in proportions of slow-twitch and fast-twitch skeletal muscle fibres. People with more slow-twitch fibres may be able to develop greater endurance from aerobic exercise, whereas people with more fast-twitch fibres may be able to develop greater muscle size and strength from anaerobic exercise.
- Some adverse effects may occur if exercise is extremely intense and the body is not given proper rest between exercise sessions. Many people who overwork their muscles develop delayed onset muscle soreness (DOMS), which may be caused by tiny tears in muscle fibres.
12.5 Review Questions
- How do we define physical exercise?
- What are current recommendations for physical exercise for adults?
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- Define flexibility exercise, and state its benefits. What are two examples of flexibility exercises?
- In general, how does physical exercise affect health, quality of life, and longevity?
- What mechanism may underlie many of the general health benefits of physical exercise?
- Relate physical exercise to cardiovascular disease risk.
- What may explain the positive benefits of physical exercise on cognition?
- How does physical exercise compare with antidepressant drugs in the treatment of depression?
- Identify several other health benefits of physical exercise.
- Explain how genetics may influence the way individuals respond to physical exercise.
- Can too much physical exercise be harmful?
12.5 Explore More
How playing sports benefits your body … and your brain – Leah Lagos and Jaspal Ricky Singh, TED-Ed, 2016.
The surprising reason our muscles get tired – Christian Moro, TED-Ed, 2019.
What makes muscles grow? – Jeffrey Siegel, TED-Ed, 2015.
Why some people find exercise harder than others | Emily Balcetis, TED, 2014.
Attributions
Figure 12.5.1
stroller fit by Serge Melki from Indianapolis, USA on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 12.5.2
Children kayaking young sport by Hagerty Ryan, USFWS on Pixnio is used under a public domain (CC0) Certification (https://creativecommons.org/licenses/publicdomain/).
Figure 12.5.3
Bicep curls [photo] by Senior Airman Jarrod Grammel from U.S. Moody Air Force Base is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 12.5.4
Flexibility exercise by carl-barcelo-nqUHQkuVj3c [photo] by Carl Barcelo on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 12.5.5
Canadian women’s double scull silver Rio 2016 by Gerhard Pratt on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 12.5.6
Toronto Marathon 2012 by Marc Roberts on Flickr is used under a CC BY-NC-SA 2.0 (https://creativecommons.org/licenses/by-nc-sa/2.0/) license.
Figure 12.5.7
Muscle damage in military recruits by Lance Cpl. Bridget M. Keane from the United States Marine Corps Recruit Depot is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Elwood, P., Galante, J., Pickering, J., Palmer, S., Bayer, A., Ben-Shlomo, Y., Longley, M., & Gallacher, J. (2013). Healthy lifestyles reduce the incidence of chronic diseases and dementia: evidence from the Caerphilly cohort study. PloS one, 8(12), e81877. https://doi.org/10.1371/journal.pone.0081877
Mayo Clinic Staff. (n.d.). Amenorrhea [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/amenorrhea/symptoms-causes/syc-20369299#
Mayo Clinic Staff. (n.d.). Coronary artery disease [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/coronary-artery-disease/symptoms-causes/syc-20350613
TED-Ed. (2016, June 28). How playing sports benefits your body … and your brain – Leah Lagos and Jaspal Ricky Singh. YouTube. https://www.youtube.com/watch?v=hmFQqjMF_f0&feature=youtu.be
TED-Ed. (2019, April 18). The surprising reason our muscles get tired – Christian Moro. YouTube. https://www.youtube.com/watch?v=rLsimrBoYXc&feature=youtu.be
TED-Ed. (2015, November 3). What makes muscles grow? – Jeffrey Siegel. YouTube https://www.youtube.com/watch?v=2tM1LFFxeKg&feature=youtu.be
TED. (2014, November 14). Why some people find exercise harder than others | Emily Balcetis, YouTube. https://www.youtube.com/watch?v=QeIrdqU0o9s&feature=youtu.be
Wikipedia contributors. (2020, August 1). Delayed onset muscle soreness. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Delayed_onset_muscle_soreness&oldid=970682631
Any bodily activity that enhances or maintains physical fitness and good health.
Any physical activity in which muscles are used well below their maximum contraction strength but for a relatively long period of time, consuming a large amount of oxygen.
Any physical activity in which muscles are used at close to their maximum contraction strength but for a relatively short period to time, consuming a small amount of oxygen.
Any physical activity that stretches and lengthens muscles.
One of several hundred cytokines or other small proteins produced and released by muscle cells (myocytes) in response to muscular contractions with an endocrine function.
A glucocorticoid hormone produced by the cortex of the adrenal gland that is released in response to stress and also helps control metabolic rate, suppression of the immune system, and other functions
A persistently high blood pressure, generally defined as 140/90 mm Hg or higher.
A type of disease in which cells of the central nervous system stop working or die. Neurodegenerative disorders usually get worse over time and have no cure. They may be genetic or be caused by a tumor or stroke.
A chronic or persistent disorder of the mental processes caused by brain disease or injury and marked by memory disorders, personality changes, and impaired reasoning.
A common and serious medical illness that negatively affects how you feel, the way you think and how you act. Fortunately, it is also treatable. Depression causes feelings of sadness and/or a loss of interest in activities once enjoyed. It can lead to a variety of emotional and physical problems and can decrease a person’s ability to function at work and at home.
A neurotransmitter or other chemical substance that affects the nervous system.
A type of drug that tends to induce a feeling or state of intense excitement and happiness.
A sleep disorder in which one has trouble falling and/or staying asleep.
The body system in humans and other animals that protects the organism by distinguishing foreign tissue and neutralizing potentially pathogenic organisms or substances.
A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.
A multifactorial disorder in which a combination of insulin resistance and impaired insulin production lead to loss of glucose control and high levels of blood glucose.
Abnormal or excessive fat accumulation that presents a risk to health. Obesity has been more precisely defined by the National Institutes of Health (the NIH) as a BMI (Body Mass Index) of 30 and above.
A type of skeletal muscle cell that is mainly responsible for aerobic activities such as long-distance running.
A type of skeletal muscle cell that is mainly responsible for anaerobic activities such as weight lifting.
A double-membrane-bound organelle found in most eukaryotic organisms. Mitochondria convert oxygen and nutrients into adenosine triphosphate (ATP). ATP is the chemical energy "currency" of the cell that powers the cell's metabolic activities.
A red protein containing heme, which carries and stores oxygen in muscle cells. It is structurally similar to a subunit of hemoglobin.
Respiration using electron acceptors other than molecular oxygen. Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
A type of chemical that transmits signals from the axon of a neuron to another cell across a synapse.
The central nervous system organ inside the skull that is the control center of the nervous system.
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