To the Editor: Previous articles in the Journal have stressed the importance of making obesity prevention a public health research priority.1,2 Participation in physical activity is one important factor in counteracting increase in body weight.3 While recent studies have focused on environmental factors that influence walking (eg, presence of paths and trails, accessibility of destinations)4 and the possibility of environmental innovations to increase rates of participation, few studies have investigated participants’ perception and understanding of variation in physical activity in relation to environmental factors across the seasons.

Our study aimed to examine how people perceive the impact of changes in ambient temperature and hours of daylight across the seasons on their rates of physical activity. We compared residents of the southern and northern hemispheres: a group of women from Sydney, Australia (n = 121; mean age, 19 years [SD, 2 years]), and a group of women from Trier, Germany (n = 109; mean age, 21 years [SD, 3 years]). Participants completed a brief written survey specifically designed for our study. The survey, using an “open question” format, asked participants to describe and explain any perceived changes in their physical activity during winter and summer.

The majority of Australians and Germans perceived seasonal changes in physical activity (73.6% and 71.6%, respectively), with no significant difference between the two groups. These changes typically entailed a decrease in physical activity levels during winter (noted by 55.2% and 66.2% of Australians and Germans, respectively). A significantly higher number of Australians than Germans perceived a change from outdoor activities (eg, swimming) to indoor activities (eg, squash) between summer and winter (χ1 = 9.21; P = 0.002). Significantly more Germans than Australians perceived themselves to be affected by environmental factors (χ1 = 9.37; P = 0.002).

These results support the contention that environmental changes are linked to changes in activity levels,5 and that more extreme climatic changes (such as those experienced by Germans compared with Australians) are associated with a greater perceived impact on levels of physical activity.

Programs aiming to encourage greater participation in physical activity in winter need to challenge people’s perception of the impact of environmental factors by offering indoor opportunities for exercise, particularly to people from Germany. It appears that Australians are more aware of indoor opportunities for physical activity. Research into environmental factors that encourage or discourage walking4 needs to be taken into account when designing programs to enhance physical activity across the seasons. For example, constructing walking or cycling paths in the neighbourhood may encourage people to continue with indoor activities during the colder seasons by making the indoor venues more easily accessible.