Where There's a Wheel, There's a Way
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH, Clinical Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips is a consultant for Cephalon, and serves on the speakers bureaus for Resmed and Respironics.
Synopsis: The more bike riding a premenopausal women does, the less likely she is to gain weight.
Source: Lusk AC, et al. Bicycle riding, walking, and weight gain in premenopausal women. Arch Intern Med 2010;170:1050-1056.
This report comes from the Nurses' Health Study II (NHSII), which is an ongoing study of more than 100,000 U.S. female nurses who were 25-42 years in 1989. Participants have completed questionnaires about their medical history and lifestyle every other year since then. The overall response rate has been approximately 90% over the nearly 20 years of follow-up.
For purposes of this analysis, the investigators used data from women who were still premenopausal in 2005. They excluded those who had recently been pregnant, those from whom data about weight or physical activity were missing, those who reported extreme weight values or weight changes, those who had physical conditions preventing exercise, those who reported exercising more than 4 hours a day, and those who had had myocardial infarction, stroke, angina, cancer, or diabetes. They were left with 18,414 healthy premenopausal women for analysis.
Data about the amount and kind of physical activity were collected in detail in 1989 and in 2005. The respondents were asked about walking or hiking outdoors, jogging, running, bicycling (including on a stationary machine), calisthenics/aerobics/aerobic dance/rowing machine, tennis/squash/racquetball, lap swimming, or other aerobic activity (e.g., lawn mowing and stair climbing). Women categorized each physical activity by duration per week. Bicycling in 1989 and 2005 was categorized into 4 groups (0, ≤ 5, 5-15, and > 15 min/day).
Sedentary behavior was assessed by the following questions: "How many hours per week do you spend: 1) Sitting at home while watching TV/VCR?" 2) "Other sitting at home (e.g., reading, meal times, and at desk)?" The main outcome was the weight change between 1989 and 2005. A secondary outcome was gaining more than 5% of weight from baseline in 1989 by 2005. Eating behavior known to predict weight gain (intakes of sugar-sweetened beverages, energy-adjusted trans fats, and energy-adjusted dietary fiber) was included in the analysis, as were alcohol consumption at baseline, smoking, oral contraceptive use, parity, and antidepressant intake.
Nearly half (48%) of the women reported they spent some time bicycling in 2005 (this could include stationary biking), but the average time they bicycled was only 2.5 min/day. Of the bicyclists, only 13% bicycled for at least 10 min/day. Participants reported spending much more time walking briskly than biking (average about 16 min/day), and overweight women reported walking more slowly than normal weight women. The mean time spent sitting at home was about 5 times (about 2.5 hours/day) more than the time spent doing any kind of physical activity (about 0.5 hour/day), and overweight women spent the most time sitting at home.
Over the 16 years of follow-up, the group of women gained an average of 9.3 kg (20.5 lbs) Women who were not overweight to begin with (BMI < 25 kg/m2) gained much less weight (8.4 kg vs 12.6 kg). Over the 16 years of study, the women as a group decreased the mean time they spent doing physical activity by about 8.5 min/day. Not surprisingly, those women who increased their total daily physical activity over the course of the study gained less weight; similarly, increased time sitting at home was associated with greater weight gain. In terms of biking, very few women (1.2%) actually increased bicycling over the course of the study, but for those who did, protection from weight gain was substantial. For women who did not bike at all in 1989 but who had started bicycling by 2005, even 5 min/day of biking was associated with statistically significantly smaller weight gain; the more a woman biked, the less weight she gained, controlling for many confounders. The mean weight gain was the smallest (5.5 kg) in women who engaged in 4 hours/wk or more of bicycling compared with women who bicycled for less time. Of note, the benefits of brisk walking, bicycling, and other physical activities were significantly greater among overweight and obese women (BMI ≥ 25 kg/m2) than for normal weight women. Of the physical activities assessed, only slow walking (< 2 mph) showed no benefit in preventing weight gain.
Commentary
Among the most notable findings of this study were how few women actually increased their biking by 30 min/day (about 1%), and that the study is all about reducing the amount of weight gain, not reducing the amount of weight. It was not possible for me to determine from the data provided how many women actually lost weight or what the correlates of that were, but it is clear that very few women lost, or even maintained their weight.
Nevertheless, the odds of doing so were enhanced by any kind of physical activity except for slow walking. In their excellent discussion, the authors undertake some sensible and gentle advocacy, pointing out that, "Unlike discretionary gym time, bicycling could replace time spent in a car for necessary travel ... for activities of daily living. Bicycling could then be an unconscious form of exercise because the trip's destination, and not the exercise, could be the goal." They review several studies of bicycling and weight in men, and point out that little work has been done to assess the effect of bicycling and weight gain in women. They also discussed the emphasis on walking, as opposed to biking, in the United States, and the lack of appropriate bike paths, particularly for women, in the United States. It turns out that the bike paths that exist in the United States were designed primarily by and for men, and that women prefer different kinds of bike paths than men do; women want the paths to be separated from motorized vehicular traffic.1,2 The authors speculate that this could result in exercise-minded women choosing to walk, rather than bike, for transportation. In support of this notion is the contrast between the United States and the Netherlands with regard to commuting. In the Netherlands (and much of Europe), specifications for bike paths recommend separate cycle tracks parallel to road with high speed limits, for example. Perhaps as a result, 22% of the population walks and 27% commutes by bicycle.3 In the United States, 9% of the population walks for commuting, whereas only 0.5% commutes by bicycle.4
Another implication of this study is that walking may not confer the benefit some walkers expect. Slow walking was not associated with reduced weight gain, and overweight women were much more likely to be slow walkers.
References
1. American Community Survey: Sex of workers by means of transportation to work. U.S. Census Bureau; 2007.
2. Garrard J, et al. Promoting transportation cycling for women. Prev Med 2008;46:55-59.
3. Pucher J, Buehler R. Making cycling irresistible. Transp Rev 2008;28:495-528.
4. Bassett DR Jr, et al. Walking, cycling, and obesity rates in Europe, North America, and Australia. J Phys Act Health 2008;5:795-814.
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