Physical Activity for Health: What Kind? How Much? How Intense?

A conversation with Dr. Steven Blair

The health benefits of physical activity are numerous and extend well beyond weight management. Yet, many people do not exercise on a regular basis. Both the United States and the European Union issued physical activity guidelines in 2008. Since then, the evidence supporting the role of physical activity in health has continued to expand.

The Coca-Cola Company Beverage Institute for Health and Wellness (BIHW) recently spoke with renowned researcher Steven Blair, PhD, University of South Carolina, who provided new insights on physical activity and health as well as his perspectives on motivating the public to be more physically active.
Expand All | Collapse All
  • How strong is the evidence for physical activity in weight management?
    • Dr. Blair: The strength of evidence varies depending on whether the end point being evaluated is weight loss, weight maintenance after weight loss, or simply the prevention of weight gain.

      There is very strong evidence to support the role of physical activity in preventing weight gain, and it’s clear that by adding physical activity, people lose more weight over weeks and months than with caloric restriction alone. However, in overweight or obese individuals, it appears caloric restriction is more effective than physical activity, at least initially. Now, if you think about that, it makes a lot of sense. For someone who is overweight or obese and out of shape, it may be more feasible to reduce caloric intake by 500 calories or more than to engage in enough activity to burn 500 calories daily. However, with slow increases in physical activity, fitness level gradually improves, and more calories can then be burned through higher intensity or longer bouts of physical activity.

      In terms of weight maintenance after losing weight, physical activity seems to play a very crucial role, although we don’t yet have randomized trials. Research indicates that people who have lost over 50 pounds (23 kilograms)—or more than five percent of body weight—and kept it off more than two years, engage in substantial amounts of physical activity. Many people need to do more than 300 minutes of moderate-intensity activity per week to prevent weight regain.
  • Is physical activity related to other health outcomes?
    • Dr. Blair: Yes, very much so. We see strong evidence for the role of physical activity in reducing risk of heart disease, stroke, diabetes, hypertension, colon and breast cancers, excessive weight gain, injurious falls, cognitive impairment, and depression. (See Table 1)

      Physical activity is the principle determinant of fitness, which is a powerful predictor of all-cause mortality, including who’s going to die of cardiovascular disease. In fact, poor fitness accounts for substantially more deaths than other modifiable health factors, including obesity, smoking, high cholesterol and diabetes, especially in older people. So, for individuals to retain physical and mental functioning and independence in later years, physical activity is the best insurance.
  • Are the health benefits of physical activity due to its role in weight management?
    • Dr. Blair: No. In fact, I believe both health professionals and the public need to think more about all the health benefits of physical activity, and focus less on weight management because many health benefits come with physical activity, whether a person loses weight or not.
  • Are body weight and BMI associated with fitness level?
    • Dr. Blair: Yes, but association between body weight, BMI and fitness level is not as tight as many people believe. For example, almost all people with BMIs of 21-22 are fit. However, as BMI increases, the correlation is less strong. This is the “fit but fat” paradox, in that overweight and even obese people can be fit and at low risk for obesity-related health problems.

      Although this may seem counterintuitive to some, there is abundant evidence that clearly shows that physically active people who are overweight (BMI 25-29.9) or in the low range of obesity (BMI 30-34.9) do not have the obesity-related health risks seen in their unfit counterparts. And in fact, individuals who are overweight or obese but fit have substantially lower mortality risk than normal weight individuals who are unfit. Our research and other studies indicate that even with BMIs up to the upper 30s, people who are active and fit do not have elevated mortality risk.

      This is why understanding an individual’s fitness level is critical in assessing his or her health risks.
  • Do you think we place too much emphasis on body weight and BMI?
    • Dr. Blair: Yes, I do. For the past 30 years, public health efforts have emphasized the detrimental effects of obesity, using BMI as a standard. Yet, obesity rates have not declined, although they may have leveled off a bit. So we have to ask if the strategies are flawed.

      I’d like to see a shift. Let’s stop obsessing about weight and worshiping the thin, ideal body type, which most of us will never achieve no matter what we do. Let’s stop demonizing obesity, reduce bias and stigmatization, and focus on what people can do to improve their health: Eat more fruits, vegetables and whole grains, and be active most days.
  • How much physical activity is needed to gain health benefits?
    • Dr. Blair: The 2008 Physical Activity Guidelines state, “Some physical activity is better than none,” and as we discussed, adults who participate in any amount of physical activity gain health benefits.

      With that said, the Guidelines do specify physical activity targets that are associated with optimum benefits for different healthy populations. For adults, the weekly target is 150 minutes of moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity. (See Table 2 for examples of different activities and intensities). With some health outcomes such as risk reduction for breast cancer, the level of weekly physical activity recommended is higher: 300 minutes of moderate activity or 150 minutes of intense activity. Of course, 75 minutes of medium-intensity exercise is clearly better than none, in terms of fitness and other health benefits.

      We conducted a trial with post-menopausal women and found a strong linear gradient between fitness and the amount of exercise. With 75 minutes of moderate activity per week we saw fitness increase by about five percent.
  • Are long bouts (>20 minutes) of physical activity necessary to obtain health benefits?
    • Dr. Blair: No. There’s a common but inaccurate belief that a certain intensity or duration of exercise is necessary to gain health benefits. In terms of health benefits with exercise, we’ve moved away from the concept of getting your heart rate up for 20 minutes. Instead, for health benefits, the current recommendation is to achieve moderately to vigorously intense physical activity in bouts of at least 10 minutes. For example, an individual could meet the recommended 150 minutes a week of physical activity through three 10-minute bouts of moderately to vigorously intense physical activity a day, five days a week.

      While current recommendations focus on a minimum weekly amount of physical activity, it’s probably a good idea to do something on most days. Immediate benefits of activity such as insulin sensitivity or decreased blood pressure persist for an hour or even a day or two. And from a behavioral aspect, it makes sense to get some activity every day. If you wait to exercise only on weekends, you never know if a torrential rain storm or blizzard might cause you to miss your exercise window.
  • Do light activities provide any health benefits?
    • Dr. Blair: Whether health benefits can be gained with light activities is an emerging area of research. A new line of research suggests that just standing up and moving around a little bit is better for you than sitting for long periods. For now, it’s critical that we get people at least aware of the health benefits associated with getting 150 minutes of moderate or 75 minutes vigorous physical activity per week.
  • What is your advice for health professionals working with sedentary individuals?
    • Dr. Blair: Musculoskeletal soreness is typical when beginning exercise, and keep in mind, many sedentary people have musculoskeletal problems anyway. By starting out slowly and building up gradually over a period of weeks, most problems can be avoided. A person can start with 10 minutes per day and build up to 150 minutes per week.

      Sudden cardiac arrest can occur with physical activity, but is extremely rare. And, of course, it occurs outside of exercise as well. It’s important to note that people who are regularly physically active are much less likely to die of sudden cardiac arrest than people who are sedentary. Yes, risk is elevated during physical activity. However, over a 24-hour period, risk of sudden cardiac arrest is substantially less for exercisers than for people who are sedentary.

      It’s important to know the early warning signs of cardiac problems. If a person engaging in exercise experiences chest tightness or pain radiating down the arm, he/she needs to stop, and, if the symptoms persist, get medical attention.

      The bottom line is that for people engaging in 150 minutes per week of moderate physical activity, the health risks are quite minimal and the benefits far outweigh the risks.
  • What are research needs for better understanding physical activity and health?
    • Dr. Blair: We need to learn more about the independent effects of light activity and being sedentary, in terms of health. And while we have extensive research about the impact of aerobic physical activity, we need a better understanding of the health outcomes associated with strength and resistance training. For example, we conducted a study of men who had been diagnosed with hypertension, and those who were physically stronger were less likely to die. We need to understand more about that relationship, especially in older adults.

      We also need more research about the effects of combining resistance training and aerobics. In one study, Dr. Tim Church looked at three groups that engaged in the same amount of activity per week. We saw better physiologic adaptation for a group that combined aerobics with strength training versus either a group that did only resistance training or a group that did only aerobics.

      The physical activity guidelines do not address the health benefits of flexibility, but it’s clear that maintaining flexibility helps retain functionality, especially as we age. But we need more research about the potential benefits of stretching.

      There may be some additional health benefits associated with short high-intensity bouts of exercise – going all out for two minutes – but we need a better understanding.

      A very exciting area of research is the effect of exercise on the brain. Recent evidence shows physical activity is good for the brain, especially for older people. And exercise seems to be good for kids’ brains. Some research shows that regular exercise improves executive function (the mental processes that help us plan and organize) and that kids who are active do better academically. While research about exercise and the brain is still in its infancy, the evidence so far shows that the benefits seem to apply across the lifespan.
  • What are bottom-line recommendations for physical activity and health?
    • Dr. Blair: First, we need to get the message out that regular physical activity is one of the best things you can do for your health. It helps promote well-being, reduce risk for disease and preserve mental and physical functioning.

      Second, current recommendations are that all adults should get at least 150 minutes of moderate physical activity or 75 minutes of vigorous physical activity per week, or a combination of moderate and vigorous with one minute of vigorous being equal to two minutes of moderate intensity.
  • Table 1

      • Health Benefits of Physical Activity—A Review of the Strength of the Scientific Evidence

        Adults and Older Adults

        Strong Evidence

      1. Lower Risk of:
      2. Early death
      3. Heart disease
      4. Stroke
      5. Type 2 diabetes
      6. High blood pressure
      7. Adverse blood lipid profile
      8. Metabolic syndrome
      9. Colon and breast cancers
      10. Prevention of weight gain
      11. Weight loss when combined with diet
      12. Improved cardiorespiratory and muscular fitness
      13. Prevention of falls
      14. Reduced depression
      15. Better cognitive function (older adults)

        16. Moderate to Strong Evidence

      16. Better functional health (older adults)
      17. Reduced abdominal obesity

        18. Moderate Evidence

      18. Weight maintenance after weight loss
      19. Lower risk of hip fracture
      20. Increased bone density
      21. Improved sleep quality
      22. Lower risk of lung and endometrial cancers

        23. Children and Adolescents

        Strong Evidence

      23. Improved cardiorespiratory endurance and muscular fitness
      24. Favorable body composition
      25. Improved bone health
      26. Improved cardiovascular and metabolic health biomarkers

        27. Moderate Evidence

      27. Reduced symptoms of anxiety and depression

        28. 2008 Physical Activity Guidelines for Americans, At-a-glance Fact Sheet for Health Professionals. US Department of Health & Human Services., Washington DC, October 2008. http://www.health.gov/paguidelines/factsheetprof.aspx, accessed May 15, 2011.

  • Table 2

      • Examples of Different Aerobic Physical Activities and Intensities

        Moderate Intensity

      1. Walking briskly (3 miles per hour or faster, but not race-walking)
      2. Water aerobics
      3. Bicycling slower than 10 miles per hour
      4. Tennis (doubles)
      5. Ballroom dancing
      6. General gardening

        7. Vigorous Intensity

      7. Racewalking, jogging, or running
      8. Swimming laps
      9. Tennis (singles)
      10. Aerobic dancing
      11. Bicycling 10 miles per hour or faster
      12. Jumping rope
      13. Heavy gardening (continuous digging or hoeing, with heart rate increases)
      14. Hiking uphill or with a heavy backpack

        15. Note:This table provides several examples of activities classified as moderate-intensity or vigorous-intensity, based on absolute intensity. This list is not all-inclusive. Instead, the examples are meant to help people make choices.

        2008 Physical Activity Guidelines for Americans, At-a-glance Fact Sheet for Health Professionals. US Department of Health & Human Services., Washington DC, October 2008. http://www.health.gov/paguidelines/factsheetprof.aspx, accessed May 15, 2011.

  • References
Expand All | Collapse All

Biography

Steven N. Blair, PED



Steven N. Blair is Professor in the Departments of Exercise Science and Epidemiology and Biostatistics at the Arnold School of Public Health, University of South Carolina, and a Benjamin Meaker Fellow at the University of Bristol, England. Dr. Blair is a Fellow in the American College of Epidemiology, Society for Behavioral Medicine, American College of Sports Medicine, American Heart Association, and American Academy of Kinesiology and Physical Education; and was elected to membership in the American Epidemiological Society.

Dr. Blair is a past-president of the American College of Sports Medicine (ACSM), National Coalition for Promoting Physical Activity, and the American Academy of Kinesiology and Physical Education. Dr. Blair is the recipient of three honorary doctoral degrees--Doctor Honoris Causa degree from the Free University of Brussels, Belgium; Doctor of Health Science degree from Lander University, U.S.; and Doctor of Science Honoris Causa, University of Bristol, UK. He has received awards from many professional associations, including a MERIT Award from the National Institutes of Health, ACSM Honor Award, Population Science Award from the American Heart Association, and is one of the few individuals outside the U.S. Public Health Service to be awarded the Surgeon General's Medallion. He has delivered lectures to medical, scientific, and lay groups in 48 states and 50 countries. His research focuses on the associations between lifestyle and health, with a specific emphasis on exercise, physical fitness, body composition, and chronic disease. He has published over 500 papers and chapters in the scientific literature, and was the Senior Scientific Editor for the U.S. Surgeon General's Report on Physical Activity and Health.

Additional Resources

Exercise is Medicine Archived Webinar

Move It! Free Continuing Education Self-Study

Highlights from the 2008 Physical Activity Guidelines for Americans

2008 Physical Activity Guidelines for Americans, US Department of Health & Human Services., Washington DC, October 2008

European Union Physical Activity Guidelines

Evidence-Based Guidelines for Cardiovascular Disease Prevention in Women: 2007 Update, American Heart Association.

Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, National Heart, Lung, and Blood Institute.

Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), National Heart, Lung, and Blood Institute.

The views and opinions expressed by the experts and organizations quoted in this article are their own and do not necessarily represent the views of any institution or association to which they belong, nor The Coca-Cola Company.