The relationship between leisure, walking, and transportation activity with the natural environment
Introduction
Despite the well-documented benefits of a physically active lifestyle, in the US a large percentage of the population does not engage in sufficient levels of physical activity to confer health benefits as recommended by the US Surgeon General (at least moderate intensity physical activity, for at least 30 min a day, on most, preferably all, days of the week) (USDHHS et al., 1996; Pate et al., 1995). Recently, several researchers have underscored the importance of environmental influences on physical activity behavior (Breslow, 1996; Sallis and Owen, 1997; Hill et al., 2001; Pikora et al., 2003; Booth et al., 2001; McLeroy et al., 1988). Most attention has been focused on walkability (Saelens et al., 2003a, Saelens et al., 2003b; Giles-Corti and Donovan, 2002a), access (King et al., 2003; Humpel et al., 2004; Huston et al., 2003; Powell et al., 2003; Brownson et al., 2001), and sprawl (Lopez, 2004; Ewing et al., 2003); however, characteristics of a neighborhood's natural environment, such as weather, hills, trees for shade and exhaust fumes, may also play an important role in an individual's decision to be physically active.
Aspects of the weather, such as heat, humidity, and cold may affect outdoor activity levels by modifying how hard one is able to exercise and the perceived effort needed to be active (American Heart Association, 2003; Health on the Net Foundation, 2003). Heat and humidity interfere with the body's natural cooling process and increases the risk of dehydration, heat exhaustion, and heat stroke (American Heart Association, 2003; The President's Council in Physical Fitness and Sports et al., 1987). Cold weather causes constriction of surface blood vessels which elevates blood pressure causing more strain on the heart as well as decreased muscle power (Health on the Net Foundation, 2003). Precipitation, wind, and number of daylight hours are other weather-related environmental factors that may affect physical activity, as people are not likely to participate in outdoor activities when it is raining, snowing, icy, windy, or dark.
Studies in the public health literature have investigated the effect that weather has on physical activity levels in the US by comparing physical activity levels at different times of the year. (Dannenberg et al., 1988; Pivarnik et al., 2003; Levin et al., 1999; Matthews et al., 2001; Centers for Disease Control and Prevention (CDC), 1997). Generally, these studies conclude that the frequency and duration of leisure activity decreases during winter months compared to warmer months, presumably attributable to coincident changes in monthly temperature, daylight, and precipitation. Despite associations between leisure activity and seasonality, weather has generally not been found to be a barrier to physical activity when controlling for other potential confounders. King et al. (2000) found that weather was not reported to be a strong personal barrier to physical activity, and consequently was not independently associated with physical activity among a sample of US adult women. Two other studies of adults also found that perceiving weather as a barrier to physical activity was not independently associated with meeting recommendations for physical activity (Parks et al., 2003) or vigorous activity (Sallis et al., 1989). One study of Australian adults did report that perception of weather as a barrier to physical activity was associated with an increased likelihood of reporting more sedentary behavior (Salmon et al., 2003).
Evidence of the potential effect weather has on physical activity can also be found in the transportation literature where they have explored the effect of weather and climate on bicycle commuting in countries outside of the US. Generally, it has been found that inclement weather has more of an adverse affect on recreational bike trips than for commuting trips (Hanson and Hanson, 1977; Richardson, 2000; Nankervis, 1999) and that bikers are less likely to ride on days of extreme temperatures, rain, and wind (Richardson, 2000).
The degree of hilliness in an area can also impact outdoor activity by increasing the intensity of physical activity. Since the perceived effort of traversing up hills is greater than on level surfaces, this may lead to the avoidance of jogging, biking, or walking in neighborhoods that are hilly. Past research found no association between walking (Eyler et al., 2003), a positive association between leisure activity (King et al., 2000; Wilcox et al., 2000) and meeting recommendations for moderate and vigorous activity (Brownson et al., 2001) and the perceived presence of hills.
Studies in the transportation field have investigated the association between objective measures of hills and physical activity. Cervero and Duncan (2003) found that higher slopes (hills) deterred both walking and biking. However, the authors only took into account the degree of slope at the origin and destination of a trip; therefore, potentially underestimating the importance of hills on walking and biking. Rodriguez and Joo (2004) examined travel mode choice in a sample of university adults. The difference in travel time was calculated with and without accounting for slope and they found that sloping terrain was negatively related to one's propensity to walk or bike. Although this study was the first to examine the relationship between slope and travel mode along an entire route; the authors do not describe how the calculations were conducted. Another study that utilized objective measurement for the presence of hills was also the first study to combine perception and objective measures of hills (Troped et al., 2001). This study used Geographic Information Systems (GIS) to categorize the slope of the shortest route between the participant's home and a trail and found moderate agreement between this objective measure and self-report of steep hills (kappa=0.41, 95% CI 0.33, 0.50). They also found that the perception of having to negotiate a steep hill was not associated with use of the trail; however, those participants who were classified as not having to negotiate a steep hill using the objective measure of a steep hill were almost twice as likely to use the trail.
Trees along the street that provide shade may also be an important aspect of the natural environment to consider. It is hypothesized that streets lined with trees that provide shade may make for a more conducive environment for outdoor activity. Although several studies have used score indices to rate the pleasantness of the environment, which may or may not contain information on trees and shade, few studies have examined actual tree coverage as an independent factor. Hoehner et al. (2005) examined perception of trees along neighborhood streets and found no association with transportation or recreational activity. They also utilized an audit instrument to objectively measure the number of street segments that contained trees, which was combined into a summary measure of esthetics. It was found that the more esthetically pleasing the environment, the more likely adults were to report any transportation activity; however, this measure was not associated with leisure activity. In a cross-sectional survey conducted in Australia, an audit instrument was used to measure quantity of traffic and tree density simultaneously. No association was found between this combined objective measure of traffic and trees and exercising as recommended (Giles-Corti and Donovan, 2002a), or walking at recommended levels (Giles-Corti and Donovan, 2003).
Lastly, exhaust fumes or other forms of air pollution may also prohibit individuals from being physically active outdoors. Although several studies have assessed perceptions of heavy traffic in relation to physical activity (Kirtland et al., 2003; Giles-Corti and Donovan, 2002a, Giles-Corti and Donovan, 2002b; Troped et al., 2001; King et al., 2000; Wilcox et al., 2000; Eyler, 2003; Huston et al., 2003), only two studies of US adults have evaluated perceptions of foul air from cars as a barrier to physical activity. Perception of foul air in one's neighborhood as a personal barrier to physical activity was not associated with meeting recommendations for moderate and vigorous activity (Brownson et al., 2001) or walking activity (Eyler et al., 2003).
Though several studies have attempted to evaluate the relationship between perceptions of the natural environment and physical activity, fewer have assessed the association between objective measures of the natural environment and physical activity. Since it is not known whether perceptions of the natural environment have an independent, synergistic, or shared association with the observed environment in relation to physical activity, it is important to evaluate both perceived and objective measures of the environment in studies of physical activity, as well as to quantify any agreement between the two measures.
Understanding the interplay between perceived and actual characteristics of the natural environment, and how they relate to physical activity, is important for at least two reasons. First, if perceived and objective measures have independent effects on physical activity then researchers must take both of them into account in order to develop interventions that will have the most positive influence on physical activity levels. Second, if perceived and actual environments are highly associated but do not have independent effects on physical activity, then incorporating one of the two may suffice in the measurement of the natural environment. Consequently, this study examines the association of physical activity with perceptions of the natural environment, perceptions of whether the natural environment affects one's physical activity, and objectively measured aspects of the natural environment.
Section snippets
Source population
A cross-sectional study was conducted from January to July 2003 to examine potential environmental barriers and enablers to physical activity in adults via a random digit dialed phone survey in Forsyth County, NC and the city of Jackson, MS. The survey was approved by the Institutional Review Board at the University of North Carolina. Average length of the telephone interview was 27 min and it was written at an eighth grade reading level (±1.5 grades) as calculated with the SMOG readability
Sample characteristics
The majority of the sample was non-Hispanic White (56.4%) or non-Hispanic Black (38.5%), 15.2% of the population considered themselves to be of poor or fair general health and 13.3% had a moderate or severe disability that limited physical activity or exercise. The prevalence of physical activity, overall and by gender, is reported in Table 2. Overall, approximately 30% of respondents reported no LTPA, 45.0% reported some LTPA, but not enough to meet recommendations, and just over a quarter
Discussion
Findings from this research indicate a lack of agreement between adult perceptions of weather as a problem in the neighborhood or weather as a barrier to physical activity and objective measures of weather. Additionally, there were no associations between objectively measured weather and physical activity. Perceptions of weather as not being a problem in ones neighborhood, and not being a barrier to physical activity, were associated with a decreased odds of transportation activity, but they
Strengths and limitations
A limitation of this study is the inability to control for variables that may affect the choice an individual makes about where to live. If individuals choose to live somewhere because of the characteristics of those areas (i.e., an individual moves to a neighborhood because of the climate), it becomes difficult to separate the direction of causality between individual values, the environment, and that individual's physical activity behavior. Thus, any interpretation of the data will need to
Conclusion
This research is unique in that it has incorporated GIS with perceptions of the environment and perceptions of the environment as barriers to physical activity. In this study there was little, if any, agreement between perceived and objective measures as we defined them. Additionally, several associations were found between perceptions of the natural environment and physical activity, implying that it is important for interventions to identify and address individual's perceptions, whether or
Acknowledgements
This study was funded by a grant from the American Heart Association. The lead author was also funded, in part, by NIH, NHLBI, NRSA Training Grant No. 5-T32-HL007055. The authors would like to thank Fang Wen for her contribution via programming.
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