Health Psychology : a Textbook

lower levels of activity at baseline were women, the women had children and therefore

put on more weight). Unless experimental data is collected, conclusions about causality

remain problematic.

Do the obese exercise less? Research has also examined the relationship between

activity and obesity using a cross-sectional design to examine differences between the

obese and non-obese. In particular, several studies in the 1960s and 1970s examined

whether the obese exercised less than the non-obese. Using time-lapse photography,

Bullen et al. (1964) observed girls considered obese and those of normal weight on a

summer camp. They reported that during swimming the obese girls spent less time

swimming and more time floating, and while playing tennis the obese girls were

inactive for 77 per cent of the time compared with the girls of normal weight, who

were inactive for only 56 per cent of the time. In addition, research indicates that the

obese walk less on a daily basis than the non-obese and are less likely to use stairs or

walk up escalators. However, whether reduced exercise is a cause or a consequence of

obesity is unclear. It is possible that the obese take less exercise due to factors such as

Fig. 15-4 Changes in physical activity and obesity

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