What About Exercise?
So how does exercise relate to weight loss? Well we know that in order to lose weight you need to take in fewer calories as food than you burn through exercise and other activities. Exercise can help you burn more calories than without it, so weight loss should be helped by increased activity. While that’s true, it’s a bit more complex than that with real implications for losing weight. Before we discuss that we need to better understand some concepts that a discussion of exercise and prevention can best illustrate.
Beyond its effect on weight loss, one of the major benefits of exercise is in prevention. A recent study (1) in women underscores these key relationships. This study built upon the large Nurses’ Health Study. This study looked at data on over 88,000 women ages 39 to 59 from 1980 through 2000. None of these ladies had heart disease or cancer when the study began. Over the 20 years of the study, the women reported their diet, physical activity level and waist circumference every 2 years. The results found that women who were inactive and obese had nearly 3.5 times the risk of having coronary heart disease than those who were active and lean. The lead researcher, Dr. Frank B. Hu, noted, “A high level of physical activity did not eliminate the risk of coronary heart disease with obesity, and leanness did not counteract the increased coronary heart disease risk associated with inactivity."
Recent Recommendations For Healthy Adults
The next logical question is what kinds of activity are recommended? The answer lies in a newly published article in Circulation which is the Journal of the American Heart Association, entitled, “Physical Activity and Public Health: Update Recommendation for Adults From the American College of Sports Medicine and the American Heart Association.”(2) For all healthy adults aged 18 to 65 years of age the recommendation is a minimum of moderate intensity aerobic (endurance) physical activity for a minimum of 30 minutes on five days each week or vigorous intensity aerobic physical activity for a minimum of 20 minutes on three days each week. A common way to estimate energy expenditure for a given activity and understand what is meant by these intensity designations is to use the concept of METs or metabolic equivalents. When someone is sitting quietly, they expend 1 MET. The moderate intensity activities expend from 3.0 to 6.0 METs and the vigorous activities exceed 6 METs. In terms of METs, the minimum goal is to expend 450 to 750 METs per week in moderate intensity activities, vigorous intensity activities or a combination of the two. A person can meet the minimum by a combination of moderate and vigorous intensity activity. Moderate intensity activity is generally equivalent to a brisk walk and noticeably increases the heart rate. Vigorous intensity aerobic activity causes rapid breathing and a substantial increase in the heart rate. Jogging is one example of vigorous intensity activity. The table below gives some examples of common activities and classifies them in these categories.
MET Equivalents of Common Physical Activities
From Ainsworth, et al. 2000
| Light < 3.0 METS |
Moderate 3.0 - 6.0 METs |
Vigorous > 6.0 METs |
Walking |
Walking |
Walking, Jogging & Running |
Walking slowly = 2.0 |
Walking 3.0 mph = 3.3 |
Walking at a very, very brisk pace (4.5 mph) = 6.3 |
| |
Walking at a very brisk pace (4.0 mph) = 5.0 |
Walking/hiking at moderate pace and grade with no or light pack (<10lb) = 7.0 |
| |
|
Hiking at steep grade & pack 10-42 lb = 7.5-9.0 |
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|
Jogging at 5 mph = 8.0 |
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|
Jogging at 6 mph = 10.0 |
| |
|
Running at 7 mph = 11.50 |
Household & Occupation |
Household & Occupation |
Household & Occupation |
Sitting - using computer, work at desk using hand tools = 1.5 |
Cleaning - heavy; washing windows, car, clean garage = 3.0 |
Shoveling sand, coal, etc. - 7.0 |
Standing performing light work such as making bed, washing dishes, ironing, preparing food or store clerk = 2.0-2.5 |
Sweeping floors or carpet, vacuuming, mopping = 3.0-3.5 |
Carrying heavy loads such as bricks = 7.5 |
| |
Carpentry - general = 3.6 |
Heavy farming such as bailing hay = 8.0 |
| |
Carrying & stacking wood = 5.5 |
Shoveling, digging ditches = 8.5 |
| |
Mowing lawn - walk power mower = 5.5 |
|
Leisure Time & Sports |
Leisure Time & Sports |
Leisure Time & Sports |
| Arts & crafts, playing cards = 1.5 |
Badminton - recreational = 4.5 |
Basketball game = 8.0 |
| Billiards = 2.5 |
Basketball - shooting around = 4.5 |
Bicycling - on flat: moderate effort (12-14 mph) = 8.0 |
| |
|
fast (14-16 mph) = 10.0 |
| Boating - power = 2.5 |
Bicycling - on flat; light effort (10-12 mph) = 6.0 |
Skiing cross country - slow (2.5 mph) = 7.0 |
| |
|
fast (5.0-7.9 mph) = 9.0 |
| Croquet = 2.5 |
Dancing - ballroom slow = 3.0 |
Soccer - casual = 7.0; competitive = 10.0 |
| |
ballroom fast = 4.5 |
|
| Darts = 2.5 |
Fishing from riverbank & walking = 4.0 |
Swimming - moderate/hard = 8-11* |
| Fishing - sitting = 2.5 |
Golf - walking pulling clubs = 4.0 |
Tennis singles = 8.0 |
| Playing most musical instruments = 2.0-2.5 |
Sailing boat, wind surfing = 3.0 |
Volleyball - competitive at gym or beach = 8.0 |
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Swimming leisurely = 6.0* |
|
| |
Table tennis = 4.0 |
|
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Tennis doubles = 5.0 |
|
| |
Volleyball - noncompetitive = 3.0-4.0 |
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*MET values can vary substantially from person to person during swimming as a result of different strokes & skill levels.
The recommendation also indicates that bouts of moderate intensity aerobic activity at least 10 minutes in duration can count towards the 30 minute recommendation. Furthermore, because of the dose response relation of physical activity and health, individuals who wish to further reduce their risks for chronic diseases may do so by exceeding the minimum recommendations for activity. From the standpoint of weight loss, 60-90 minutes of moderate intensity physical activity daily seems to be necessary to maintain a weight loss of 30-50 lbs. The recommendation also calls for every adult to perform activities that maintain muscular strength or endurance at least two non-consecutive days a week. That should include 8-10 exercises involving all major muscle groups. This exercise should include sufficient weights to cause muscle fatigue after 8-12 repetitions of each exercise.
What about the risks of physical activity? As you might expect, physically active adults do experience a higher rate of leisure time and sports related injuries than those who are less active. Despite this, those that engage in moderate intensity aerobic activity have a similar overall injury rate when compared to the more sedentary individuals. It seems that the more active individuals may have more activity related injuries, but the nonsport and nonleisure injuries are less. The reverse is true for their more sedentary counterparts. As the intensity level increases, so does the risk of injuries. The risk of cardiac arrest or heart attack is low for healthy adults at the moderate intensity levels, but it increases as the intensity level increases especially for those who exercise infrequently. This underscores the importance of getting a medical clearance from one’s physician before starting any exercise program. It is recommended that, “Symptomatic persons or those with any cardiovascular disease, diabetes, other active chronic disease, or any medical concern, should consult a physician prior to any substantive increase in physical activity, particularly vigorous intensity activity.” (3)
Those Older Than 65 Or With Chronic Conditions
Another article, entitled “Physical Activity and Public Health in Older Adults: Recommendation From the American College of Sports Medicine and the American Heart Association." (4) also published in Circulation in August 2007 provides recommendations for physical activity in those over 65 or those who have chronic medical conditions, low fitness levels or physical limitations. It is similar to that for adults but also takes into account the older adult’s aerobic fitness, and recommends activities that maintain or increase flexibility and those that improve balance to prevent falls. Such an individual may progress more slowly and walking at a slow pace may be the equivalent of moderate intensity activity for them. Their muscle training should consist of more repetitions (10-15) than for their younger counterparts. This suggests that the weights should be light enough to enable them to perform 10-15 repetitions before their muscles fatigue. The flexibility training may take the form of at least 10 minutes of stretching of major muscle groups with 10-30 seconds of static stretch and 3-4 repetitions for each stretch. These should be done on the days when aerobic and strength training are done.
The point is made that exercise programs in these individuals must take into account the treatment aspects of exercise for many of the chronic conditions such as, hypertension, coronary heart disease, type 2 diabetes and elevated cholesterol to name a few. Fortunately, in many instances the therapeutic recommendations are similar to the preventive ones. However with certain conditions the emphasis may change. For example someone with osteoporosis would follow the preventive recommendation of aerobic, muscle strengthening, and balance activities, but they would emphasize weight bearing activities and possibly high impact activities, such as jumping if tolerated. Of note, not every aerobic activity is weight bearing. Swimming and cycling are not and have little, if any, preventive benefit for osteoporosis even though they are aerobic activities. They do benefit the cardiovascular and respiratory systems of the body.
The recommendation also emphasizes the fact that “There is substantial evidence that older adults who do less activity than recommended still achieve some health benefits…For example, lower risks of cardiovascular disease have been observed with just 45-75 minutes of walking per week.” (5)
Back To Exercise And Weight Loss
How does all this relate to losing weight? The key point to remember is that the MET level associated with an activity does not directly equate to the number of calories expended. The weight of the individual performing the activity will determine how many calories are expended at a given MET level of activity. So, a person who is 220 lbs. performing the same activity for the same amount of time as someone weighing 110 lbs. will burn twice as many calories as the the lighter weight individual. Since it is true that no matter what a person's weight, in order to lose 1 pound they need to have a weekly caloric deficit of 3,500 calories, the heavier person will lose the 1 pound faster! This also means that as they continue to lose weight, they will not lose weight as quickly with the same amount of exercise! To continue the rate of weight loss they must increase the amount of energy expended by increasing the number of METs or the duration of the activity. These are important points to bear in mind as you progress towards your weight loss goals.
So from this we can see that a progressive exercise program can help us lose weight throughout the weight loss and maintenance phases. But it can do more than that. Perhaps its greatest value is to prevent chronic medical conditions and help treat many conditions. All great reasons to exercise!
In the next module we will look at Healthy Eating At Home. Don't forget to take the Practice Tests.
Footnotes:
(1) Circulation. 2006;113:499-506
(2) W. L. Haskell, et al. Circulation. 2007;116:1080-1093; originally published online Aug. 1, 2007
(3) Ibid. pg. 1089
(4) M. E. Nelson, et al. Circulation. 2007;116:1094-1105; originally published online Aug. 1, 2007
(5) Ibid. pg. 1101