Exercise Overview

This article discusses the possible health benefits of exercise and movement.

One of the most obvious differences between modern life and life in the past can be found in the level of exercise. For the majority of people living in developed countries today, heavy physical exercise does not occur as a part of ordinary daily life, but must be deliberately sought out. Compare this to most of human history, in which heavy daily exercise was a requirement for survival. Even among the upper classes in 19th century Europe—to judge by a scene in Charles Dickens Pickwick Papers—going for a 10 to 20 mile walk by way of recreation was not be out of the ordinary course of events.

The human body was designed to use its physical capacities. However, for many of us, life has become a sedentary affair, moving from couch via car to office cubicle. While decreasing strenuous exercise does have some benefits, such as reducing injuries, it also presents major drawbacks. Inadequate exercise is undoubtedly a major contributor to the current epidemic of obesity, which in turn leads to diabetes, heart disease, and osteoarthritis.

Conversely, increasing one's level of exercise provides a wide variety of benefits. Besides enhancing strength and endurance and improving physical attractiveness, exercise is thought to enhance overall health as well as reduce symptoms in a number of specific ailments. However, while the many benefits of exercise appear self-evident, they can be quite difficult to provein a scientific sense. The primary problem comes down to this: it is difficult, if not impossible, to design a double-blind study of exercise.

In a double-blind, placebo-controlled study, neither patients nor researchers know who is receiving a real treatment and who is receiving a placebo.

Consider the following scenario: A study (technically, an observational or epidemiological study) may note that people in a given population who exercise more develop heart disease at a lower rate than those who exercise less. From this, it is tempting to conclude causality: that exercise reduces heart disease risk. But such a conclusion might not be correct.

Observational studies only show association, not cause and effect. Studies of the type described above had long shown that women who used hormone replacement therapy (HRT) were less likely to develop heart disease. Furthermore, use of HRT was known to improve cholesterol profile. It seemed like a "slam-dunk" case. However, to researchers' surprise, when a giant double-blind study compared hormone replacement therapy against a placebo, the results showed that use of HRT actually increased heart disease risk.

It is now hypothesized that this apparent contradiction may be due to the fact that women who use HRT are generally of higher socioeconomic status than women who do not use HRT, and that it is this socioeconomic status, and not the HRT, that was responsible for the apparent benefits seen. Whatever the reason, it is now clear that HRT does not prevent heart disease, and that the conclusions drawn from observational studies were exactly backwards. Based on this, one must at least consider the possibility that people who engage in more exercise have other qualities that protect them from heart disease, and that it is these qualities, and not the exercise, that protects them. The problem here is that while it is possible to give a placebo that convincingly resembles HRT, it is difficult to conceive of a placebo form of exercise that patients and researchers wouldn't immediately identify as different from real exercise.

Besides observational studies, other forms of scientific research involving exercise remain similarly inadequate. For example, consider the numerous studies that have been taken as proving that exercise is helpful for depression . In these studies, people who are made to exercise improve to a greater extent than those who are not interfered with. However, this finding does not prove that exercise per se aids depression. It might be, for example, that simply being enrolled in a study and motivated to do anything at all might aid depression. (This suspicion is given further weight by findings that improvement in depression is not at all related to the intensity of the exercise done—if it were the exercise itself, one would think that more intense exercise would provide greater benefits.)

Double-blind, placebo-controlled studies eliminate all of these potential confounding factors, as well as many others. However, as noted above, it is not feasible to design a double-blind study in which people are unaware (“blind” to the fact ) that they are exercising. Therefore, all results regarding the potential benefits of exercise must be taken with a grain of salt.

Where do I start?

Since brisk walking qualifies as moderately intense physical activity, that is a place to start if you are new to exercise. Before starting an exercise program, check with your doctor about any possible medical problems you may have that would limit your exercise program.

Consider making an appointment with a certified athletic trainer to help you develop a safe, effective, and enjoyable exercise program. You can find a trainer at a local gym or through a referral from your doctor or a friend. Make sure this person understands your goals and can help you maintain an exercise program that you will enjoy and stick with.

How much exercise do I need?

National health and exercise organizations recommend you do moderately intense physical activity for at least 30 minutes on most (preferably all) days of the week. Doing more vigorous exercise is also encouraged.

What kinds of exercise should I do?

To offer you the full range of benefits, your exercise program should include the major categories of exercise--aerobic (cardiovascular exercise), strength training (resistance exercises), and flexibility (stretching exercise). Within all of these major categories of exercise, there are a number of different options (see below).

Aerobic (Cardiovascular) Exercise

In aerobic exercise, you continually move large muscles in the legs and buttocks. This action causes you to breathe more deeply and your heart to work harder to pump blood, thereby strengthening your heart and lungs.

Examples include:

• Walking
• Jogging
• Running
• Aerobic dance
• Bicycling
• Swimming
• Hiking
• Playing sports that involve running, such as basketball and soccer

Strength Training (Resistance) Exercise

Strength training builds lean muscle mass, which increases your physical strength and your bone mass.

Examples include:

• Weight lifting, using:
  • Free weights
  • Weight machines
  • Elastic tubing
• Calisthenics, such as push ups or chin ups

Flexibility (Stretching) Exercise

Stretching can offer many benefits, such as improving:

• Flexibility
• Range of motion
• Circulation

Major muscle groups to stretch include:

• Back muscles
• Neck muscles
• Leg muscles: hamstrings, quadriceps, calf muscles
• Chest muscles
• Buttocks and hip muscles
• Shoulder and arm muscles
• Stomach muscles

Stretching classes include:

• Yoga
• Tai chi

Here are some tips for safe stretching:

• Spend at least 5-10 minutes warming up your muscles before stretching. For example, walking gently while swinging your arms in wide circles.
• Start each stretch slowly, exhaling as you gently stretch the muscle.
• Hold each stretch for 10-30 seconds.

Here are some common stretching mistakes to avoid:

• Do not bounce during a stretch.
• Do not stretch a muscle that is not warmed up.
• If a stretch hurts, ease up. Do not strain or push a muscle too far.
• Do not hold your breath while stretching.

Keeping the above discussion in mind, the benefits of exercise with the most solid scientific foundation include: ^{1 2 3}

• Preventing falls in the elderly

• Slightly reducing blood pressure

• Mildly improving cholesterol profile

• Enhancing survival in people with heart disease

• Improving metabolic syndrome

Regarding blood pressure, aerobic exercise has the best supporting evidence, but resistance exercise (weight training) has also shown promise. ^{4 5 6 7} One interesting study found that four 10-minute "snacks" of aerobic exercise per day were as effective at lowering blood pressure as 40 minutes of continuous exercise. ⁸ Aerobic exercise can also raise levels of HDL (“good”) cholesterol , as well as reduce levels of triglycerides . ⁹ Other conditions for which exercise has some meaningful supporting evidence of benefit include:

• Asthma ¹⁰
• Depression ¹¹
• Type 2 Diabetes (improving blood sugar control, even in the absence of weight loss) ¹²
• Fibromyalgia ¹³
• Osteoarthritis ^{14 15}

Regarding osteoporosis , the general scientific consensus is that exercise does help, but the supporting evidence is surprisingly weak. ^{16 17 18} Inconsistent or otherwise weak evidence suggests potential benefit for:

• Back pain ¹⁹
• Chronic fatigue syndrome ²⁰
• Cognitive impairment (mild dementia) ²¹
• Colon cancer prevention ²²
• Insomnia in the elderly ²³
• Stroke prevention ²⁴
• Weight loss ^{25 26}

It is widely believed that exercise improves immune function. However, there is no meaningful supporting evidence for this belief. Very high intensity exercise (such as marathon running) is known to temporarily weaken the immune system, increasing likelihood of respiratory infection. This is discussed in the article Sports and Fitness Support: Enhancing Recovery .

Evidence conflicts on whether exercise is helpful for reducing menopausal symptoms ²⁷ However, it is known that heavy exercise causes increased calcium loss through sweat, and the the body does not compensate for this by reducing calcium loss in the urine. ²⁸ The result can be a net calcium loss great enough so that it presents health concerns for menopausal women. One study found that use of an inexpensive calcium supplement (calcium carbonate), taken at a dose of 400 mg twice daily, is sufficient to offset this loss. ²⁹

1. Karmisholt K, Gyntelberg F, Gøtzche PC. Physical activity for primary prevention of disease. Systematic reviews of randomised clinical trials. Dan Med Bull. 52(2):86-9.
2. Karmisholt K, Gøtzsche PC. Physical activity for secondary prevention of disease. Systematic reviews of randomised clinical trials. Dan Med Bull. 52(2):90-4.
3. Kujala UM. Evidence for exercise therapy in the treatment of chronic disease based on at least three randomized controlled trials--summary of published systematic reviews. Scand J Med Sci Sports. 14(6):339-45.
4. Kelley GA, Kelley KS, Tran ZV. Walking and resting blood pressure in adults: a meta-analysis. Prev Med. 33(2 Pt 1):120-7.
5. Cornelissen VA, Fagard RH. Effect of resistance training on resting blood pressure: a meta-analysis of randomized controlled trials. J Hypertens. 23(2):251-9.
6. Fagard RH. Exercise is good for your blood pressure: effects of endurance training and resistance training. Clin Exp Pharmacol Physiol. 33(9):853-6.
7. Kelley GA, Kelley KS. Progressive resistance exercise and resting blood pressure : A meta-analysis of randomized controlled trials. Hypertension. 35(3):838-43.
8. Elley R, Bagrie E, Arroll B. Do snacks of exercise lower blood pressure? A randomised crossover trial. N Z Med J. 119(1235):U1996.
9. Kelley GA, Kelley KS, Tran ZV. Aerobic exercise and lipids and lipoproteins in women: a meta-analysis of randomized controlled trials. J Womens Health (Larchmt). 13(10):1148-64.
10. Ram FS, Robinson SM, Black PN. Effects of physical training in asthma: a systematic review. Br J Sports Med. 34(3):162-7.
11. Larun L, Nordheim LV, Ekeland E, et al. Exercise in prevention and treatment of anxiety and depression among children and young people. Cochrane Database Syst Rev. 2006;3:CD004691.
12. Thomas DE, Elliott EJ, Naughton GA. Exercise for type 2 diabetes mellitus. Cochrane Database Syst Rev. 3():CD002968.
13. Jones KD, Adams D, Winters-Stone K, et al. A comprehensive review of 46 exercise treatment studies in fibromyalgia (1988-2005). Health Qual Life Outcomes. 2006;4:67. Health and Quality of Life Outcomes website. Available at: http://www.hqlo.com/content/pdf/1477-7525-4-67.pdf. Accessed October 2, 2006.
14. Devos-Comby L, Cronan T, Roesch SC. Do exercise and self-management interventions benefit patients with osteoarthritis of the knee? A meta-analytic review. J Rheumatol. 2006;33:744-756.
15. Fransen M, McConnell S, Bell M. Exercise for osteoarthritis of the hip or knee. Cochrane Database Syst Rev. 2003;CD004286.
16. Kelley GA, Kelley KS. Exercise and bone mineral density at the femoral neck in postmenopausal women: a meta-analysis of controlled clinical trials with individual patient data. Am J Obstet Gynecol. 194(3):760-7.
17. Martyn-St James M, Carroll S. High-intensity resistance training and postmenopausal bone loss: a meta-analysis. Osteoporos Int. 17(8):1225-40.
18. Kelley GA, Kelley KS, Tran ZV. Exercise and bone mineral density in men: a meta-analysis. J Appl Physiol. 88(5):1730-6.
19. Hayden JA, van Tulder MW, Malmivaara A, Koes BW. Exercise therapy for treatment of non-specific low back pain. Cochrane Database Syst Rev. (3):CD000335.
20. Edmonds M, McGuire H, Price J. Exercise therapy for chronic fatigue syndrome. Cochrane Database Syst Rev. (3):CD003200.
21. van Uffelen JG, Chin A Paw MJ, Hopman-Rock M, van Mechelen W. The effect of walking and vitamin B supplementation on quality of life in community-dwelling adults with mild cognitive impairment: a randomized, controlled trial. Qual Life Res. 16(7):1137-46.
22. Samad AK, Taylor RS, Marshall T, Chapman MA. A meta-analysis of the association of physical activity with reduced risk of colorectal cancer. Colorectal Dis. 7(3):204-13.
23. Montgomery P, Dennis J. Physical exercise for sleep problems in adults aged 60+. Cochrane Database Syst Rev. (4):CD003404.
24. Oczkowski W. Complexity of the relation between physical activity and stroke: a meta-analysis. Clin J Sport Med. 15(5):399.
25. Avenell A, Brown TJ, McGee MA, Campbell MK, Grant AM, Broom J, Jung RT, Smith WC. What interventions should we add to weight reducing diets in adults with obesity? A systematic review of randomized controlled trials of adding drug therapy, exercise, behaviour therapy or combinations of these interventions. J Hum Nutr Diet. 17(4):293-316.
26. Toth MJ, Beckett T, Poehlman ET. Physical activity and the progressive change in body composition with aging: current evidence and research issues. Med Sci Sports Exerc. 31(11 Suppl):S590-6.
27. Wilbur J, Miller AM, McDevitt J, Wang E, Miller J. Menopausal status, moderate-intensity walking, and symptoms in midlife women. Res Theory Nurs Pract. 19(2):163-80.
28. Martin BR, Davis S, Campbell WW, Weaver CM. Exercise and calcium supplementation: effects on calcium homeostasis in sportswomen. Med Sci Sports Exerc. 39(9):1481-6.
29. Martin BR, Davis S, Campbell WW, Weaver CM. Exercise and calcium supplementation: effects on calcium homeostasis in sportswomen. Med Sci Sports Exerc. 39(9):1481-6.

American Orthopaedic Society for Sports Medicine website. Available at: http://www.sportsmed.org/tabs/Index.aspx . Accessed September 4, 2008.

Exercise: how to get started. American Academy of Family Physicians website. Available at: http://www.aafp.org/afp/20061215/2095ph.html . Published December 2006. Accessed September 4, 2008.

Health and fitness tips. American Council on Exercise website. Available at: http://www.acefitness.org/healthandfitnesstips/default.aspx . Accessed September 4, 2008.

Mayo Clinic. Stretching: focus on flexibility. Mayo Clinic website. Available at: http://www.mayoclinic.com/health/stretching/hq01447. Updated February 21, 2010. Accessed May 18, 2010.