The association between weight and health risk is moderated by the percentage and distribution of body fat. Studies that focus on change in weight or body composition, either alone or in addition to fitness typically measure body mass index (BMI), abdominal girth and/or percentage of body fat. Although evidence links each of these measures with mortality and morbidity, taken together they provide a more comprehensive profile of health risk. For example, there is a small gradual increase in morbidity and mortality for BMI between 25 and 30.
For BMI between 30 and 35 the risks increase more rapidly and above 35 they increase dramatically. These findings are the basis of the current definitions of overweight and obesity (overweight is defined as BMI 25-30; obesity class I is BMI between 30-35, class II is 35-40) (Tan et al, 74). However for an individual, BMI is insufficient for determining health risks, especially for people in the overweight category. This is because the metabolic effects of obesity are related to the amount, type and distribution of body fat.
People who are at greatest risk from being overweight or obese are those with centrally distributed body fat (apple shape) (Reaven, 422). Central or visceral fat has unique metabolic characteristics that increase the risk for type 2 diabetes and heart disease. For this reason measures of abdominal girth and body fat are important corollaries to BMI. When changes in weight or body fat are the outcomes of interest, physical activity is often measured in terms of calories burned.
At the individual level, calories burned can be calculated from measures of oxygen consumption per minute, however this is impractical for many studies. Therefore calories burned are typically estimated based on the person’s weight, the intensity of the activity and the amount of time spent doing the activity. For example, a 150 lb person who walks at a moderate pace for 18 minutes burns about 100 kcalories (kcals). PHYSICAL ACTIVITY Physical activity refers to “bodily movement produced by the skeletal muscles that results in energy expenditure that can range from low to high” (Dishman, 29).
Two subsets of physical activity are exercise and lifestyle. Exercise is a form of physical activity that is planned and structured. It is usually performed during one’s leisure time for the purpose of obtaining or maintaining fitness. In contrast, lifestyle physical activity (LPA) refers to everyday activities consisting of leisure, occupation and/or household as well as planned and unplanned activity. The high degree of variability in types of physical activity performed makes its assessment difficult (Dishman, 38). Exercise is categorized as either resistance or endurance.
Although both types of exercise confer health benefits, endurance activities have been more widely studied because of their association with cardiovascular disease reduction. In endurance research, the units used to measure exercise intensity are metabolic energy equivalents (METs). One MET is defined as the resting metabolic rate (3. 5 ml oxygen per kg body mass per minute). Low intensity activities such as light house work or leisurely walking have METs < 4; moderate intensity activities such as walking at a pace of 15-20 min per mile have METs of 4.
0-5. 9; and vigorous activities such as running have METs > 6 (Karmali and Shaffer, 149). With increasing fitness cardiorespiratory efficiency improves. Consequently, people with low fitness levels experience more exertion and get more benefit from low to moderate intensity activities compared with those at higher fitness levels. Physical fitness is an attribute that can be defined variously depending on whether the outcome goal is health or performance. Higher levels of physical activity are associated with increased levels of physical fitness.
Components of physical fitness that contribute to health outcomes include: cardiorespiratory endurance, muscular endurance and strength, body composition and flexibility. Higher levels of physical fitness promote cardiovascular benefits and reduce health risks. Studies that use physical fitness as their primary endpoint typically measure changes in cardiorespiratory capacity. The main measures used for this are maximum oxygen uptake (VO2 max), resting heart rate and endurance. Walking activity promotion addresses two distinct public health problems, namely inactivity and obesity.
The inextricable relationship between walking activity and weight along with society’s preoccupation with weight has resulted in walking activity being viewed as primarily a mediator of weight loss. This is unfortunate because the beneficial effects of walking activity are broader than simply weight loss and accrue at lower levels than are typically required for weight loss. Furthermore, people who are not overweight often do not appreciate their need for physical activity. Thus, there is a need to promote walking activity in a way that is appropriate to engage the general public.
One potentially effective strategy emphasizes increasing lifestyle walking activity. In contrast to traditional approaches to increasing physical activity that have promoted regular exercise, the walking approach lowers the bar so that more people are encouraged to increase activity. This strategy may also be the most realistic way of addressing the obesity epidemic. According to Hill, simply encouraging people to increase their activity by the equivalent of 100 calories a day would be sufficient to help reduce weight gain (Hill et al, 854).
Furthermore, this modest amount of activity may represent a necessary first step for helping sedentary individuals increase their fitness and self-efficacy for physical activity. Walking activity is closely associated with obesity. Low rates of walking activity coupled with over consumption of energy are believed to be the underlying causes of the obesity epidemic in the United States (Pino, 39). Currently, over 56. 4% of Americans are considered overweight or obese (Pino, 40).
The factors associated with this epidemic are complex and deeply rooted in our society, however at the individual level, weight gain results from an imbalance between energy consumption and energy utilization. Over the last 20 years, the amount of energy required for daily living in industrial countries has declined by approximately 800 kcal/day (O’Driscoll, 7). However, energy consumption has not matched this decline, and as a result the average American adult gains approximately two pounds per year.
While it is necessary to intervene on both sides of the energy balance equation, there are many who believe that targeting physical activity is essential for success. For example, Kumanyika speculates that there is: “a certain minimum level of walking activity needed in the society at large in order for the average person to maintain energy balance, and that the ability to compensate for low energy expenditure by maintaining a low level of energy consumption may be limited—particularly if the eating pattern contains energy-dense, high fat foods” (Kumanyika, 295).
From an evolutionary perspective it is clear that historically humans have been an active species. It is only within the last 100 years that walking activity has declined so significantly. Consequently, it is likely that our physiological mechanisms are better adapted for activity than sedentary behavior. The importance of walking activity to energy balance is also supported by data from the national weight loss registry. According to these data the people who are most successful at weight loss and weight loss maintenance are those who have high levels of walking activity (Pino, 41).
The exact mechanisms involved in this relationship are not completely understood, however it is clear that higher energy expenditure helps to compensate for dietary indiscretions. People who are sedentary have a very small margin for managing energy balance and this poses a problem since our society promotes energy dense foods. Thus while interventions aimed at both sides of the energy equation are necessary, I believe that physical activity may represent a threshold issue for reducing obesity. WALKING VS EXERCISE There are two main approaches to improving physical fitness.
The first is a structured approach that emphasizes regularly planned physical activity – exercise. The second utilizes a lifestyle approach, particularly walking. The walking approach differs from exercise because it is not based on prescribed regular structured activity. Instead it emphasizes accumulating 30 minutes of daily activity through everyday walking. Both methods provide similar health benefits; however, from a public health perspective, the walking approach has advantages that suggest it would be a better strategy for increasing activity among people who are sedentary.
The dominant paradigm for promoting physical activity has historically been exercise. To promote fitness, people were taught that they must exercise at 60% of maximum age-predicted heart rate (Karmali and Shaffer, 151). Tables and formulas were published so people could calculate target heart rates. However this approach has not been effective for increasing activity among the majority of the population. Epidemiological studies show that only 15% of the population is active at this level, 60% of the population is inadequately active and 25% were completely non-active (Nothwehr and Yang, 534).
One of the reasons for these low levels of activity is that people interpreted the recommendations as promoting vigorous activity, which many find both unappealing and unrealistic. Even after the recommendations were broadened lately, researchers discovered that “most people were not exercising at the amounts prescribed by the ACSM Exercise Prescription guideline because of a misperception that vigorous exercise was their only alternative” (Nothwehr and Yang, 538). High intensity activity is one of the barriers to exercise that is frequently identified.
Intensity can be a barrier both for initiating as well as sustaining physical activity. For sedentary people who intended to exercise, but did not the most common barriers were beliefs that exercise would be too physically demanding and lack of time (Dishman, 63). And, of the relatively small number of people who begin a vigorous physical activity program, at least 50% of them drop out within one year (Dishman, 66). Other barriers to exercise include: lack of time, too tiring, lack of social support, inclement weather, disruptions in routine, and lack of access to facilities.
Many of these barriers are minimized or alleviated by the lifestyle physical activity approach. Moderate rather than vigorous activity is promoted. People are encouraged to accumulate at least 30 minutes of moderate intensity activity each day (Karmali and Shaffer, 152). This can consist of short bouts or one long bout. Activities are self-selected. They can consist of everyday activities such as housework as well as structured activities. The walking approach therefore offers flexibility in meeting one’s goals. Furthermore it allows people to perform activities that are purposeful.
Two controlled studies comparing walking physical activity with structured exercise interventions found that participants in both groups had similar health outcomes. Dunn, et al. conducted a two year controlled trial in which 235 healthy sedentary people aged 35-60 years were randomized into either walking physical activity or structured activity (Dishman, 115). For each group there was a six month intensive intervention period followed by an 18 month less intensive period. The main findings for the study were that there were similar changes in physical activity and cardiorespiratory fitness over the 24 months.
In a study by Anderson et al. , 40 sedentary obese women were randomized into either lifestyle or structured physical activity interventions and were followed for one year (Dishman, 117). All women received similar dietary recommendations. At the end of the study period both groups showed similar improvements in systolic blood pressure, serum lipids, and lipoprotein levels. After 6 months the exercise group had slightly higher weight loss (8. 3 kg compared with 7. 9 kg); however, at one year the amounts were similar because the aerobic group had a higher amount of weight regain (1.
6 kg in the aerobic group compared to 0. 08 kg in the lifestyle group) (Dishman, 118). These studies help to show that lifestyle activity confers similar health benefits as traditional exercise programs. Other evidence supporting the value of walking activity comes from a meta-analysis of 127 physical activity studies by Dishman and Buckworth (Nothwehr and Yang, 535). They state that effect sizes for interventions promoting active leisure (similar to lifestyle physical activity) are larger compared with exercise programs.
Similarly, they found that studies with low intensity activities like walking reported larger effects compared with studies using higher intensities of activities (Nothwehr and Yang, 535). Walking is the most popular form of physical activity and it an integral part of lifestyle physical activity. The research not only supports the health benefits of walking, but also demonstrates the utility of promoting walking with sedentary people. In a review of data from the 2002 Behavioral Risk Factor Surveillance System (BRFSS), research found that walking was the most popular form of physical activity (Nothwehr and Yang, 535).
Furthermore the relative prevalence of walking was highest among population subgroups that report the lowest levels of participation in leisure time physical activity, such as low income, less educated, minority, elderly and overweight. The authors suggest that promotion of walking for physical activity might be an underused tool for reaching the most sedentary groups in the population. These findings were corroborated by Salmon, et al. who found that 86% of survey respondents reported high enjoyment of walking while only 31% reported high enjoyment of structured physical activity (Karmali and Shaffer, 155).
Henderson and Ainsworth performed qualitative interviews to identify perceptions of walking with African American and American Indian women. They found that attitudes toward walking were positive. Women stated that it is something that can be done anywhere and most women interviewed did not consider walking as exercise. The authors state that: “walking was noted as an important physical activity undertaken by a range of women of different ages and from different economic backgrounds and family situations” (Henderson and Ainsworth, 315). The health benefits of walking have been consistently demonstrated.
In the US Nurses Health Study, walking was inversely associated with coronary events and the relationship was stable for women irrespective of race, age or BMI (Nothwehr and Yang, 536). Similar results for men were found in the Honolulu Heart Study. Men who walked >1. 5 miles a day had half the risk of heart attack as those who walked < 0. 25 miles a day (Pino, 44). Pino summarized the literature on walking in elderly populations stating: “Walking is especially suitable for older people and can lead to improved quality of life. Among older people regular walking has been associated with lower rates of
hospitalization, lower plasma triglycerides and higher bone mineralization” (Pino, 45). Author also argues that many sedentary people are physically unable to undertake more vigorous activities because of poor cardiorespiratory fitness and/or excess weight and that for them walking is sufficiently vigorous to promote fitness. One of the hypothesized benefits of promoting walking for physical activity is sustainability. Since moderate intensity activities like walking are easily incorporated into one’s daily routine, there are fewer barriers to participation, therefore maintenance should be enhanced.
In a 32-week study where 32 sedentary adults were randomized to three groups: 1) 30 minutes of continuous brisk walking, 2) three 10 minute bouts of walking and 3) any combination of activity equaling 30 minutes, Dishman found that participants in all groups made similar gains in activity and cardiovascular improvement (Dishman, 105). Across all groups those who were able to make walking part of their daily lifestyle where more successful at meeting activity goals. In particular, participants reported that to be successful, they needed to develop the habit of choosing walking instead of sedentary activities.
Another aspect of the research was that participants stated that they were better able to meet their walking goals during the week because they encountered more unexpected time demands on weekends. WORKS CITED Daisy Tan et al. “Weight management in general practice: what do patients want? ” Medical Journal of Australia. Pyrmont, v 185(2):73-77, 2006 Harry Pino. “Physical Activity in the Management of Obesity: How Much and How Often? ” Bariatric Nursing and Surgical Patient Care. New Rochelle: Mar, 1(1):39-45, 2006 Eliza O’Driscoll. “How healthy is our world? ” Occupational Health.
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