Institutional Repository UK adults

Background: Seasonal differences in step counts have been observed in a limited number of studies conducted on US adults. Due to the diverse global climate, assessment and interpretation of seasonal patterns in ambulatory activity may vary between countries, and regionally specific studies are necessary to understand global patterns. Currently, no studies have assessed whether a seasonal trend is present when ambulatory activity is measured objectively in adults living in the UK. Aim: To investigate whether pedometer-determined step counts of adults living in the UK vary between summer and winter. Subjects and methods: Ninety-six adults (52% male, age = 41.0 ± 12.3 years, BMI = 26.1 ± 5.1 kg/m) completed a within-subject bi-seasonal pedometer study. All participants completed two four-week monitoring periods; one during the summer and one the following winter. The same Yamax SW-200 pedometer was worn throughout waking hours during both seasons, and daily step counts were recorded in an activity log. Intra-individual seasonal changes in mean daily steps were analysed using a paired samples t-test. Results: Summer mean daily step counts (10417 ± 3055 steps/day) were significantly higher than those reported during the winter (9132 ± 2841 steps/day) (p < 0.001). A follow-up study conducted the subsequent summer in a sub-sample (n = 28) reinforced this trend. Summer step counts were significantly higher than winter step counts on all days of the week (p ≤ 0.001). A significant day of the week effect was present in both seasons, with step counts reported on a Sunday being on average 1,500 steps/day lower than those reported Monday through to Saturday. Conclusion: Step counts in the sample of UK adults surveyed decreased significantly in the winter compared to the summer, suggesting future pedometer surveillance studies should capture step counts throughout the year for a non-biased reflection of habitual ambulatory activity. Public health initiatives should target these seasonal differences and opportunities should be provided which encourage individuals to increase their activity levels during the colder, darker months of the year. Introduction Obesity levels in the UK are rising, approximately 24% of male and female adults living in the UK were classified as obese in 2004 (characterised by a body mass index [BMI] ≥ 30 kg/m (WHO 2000)), compared with 14% of males and 17% of females classified as obese in 1994 (Department of Health 2005). This increasing trend is allied with a heavy financial burden on the health service, which is estimated to cost approximately £7 billion per annum (House of Commons Health Committee 2004), due to the augmented disease risk associated with excess body fat. Numerous chronic diseases including coronary heart disease, type 2 diabetes, hypertension and certain cancers can be influenced by an obese state (Haslam and James 2005). Physical inactivity is widely documented as a major risk factor for obesity (Hill and Melanson 1999), and despite attempts to disseminate this knowledge to the general population, it is predicted that about two-thirds of UK males and three-quarters of UK females do not attain physical activity levels required for health benefits (undertaking a minimum of 30 minutes of at least moderate intensity activity, at least five times per week) (Department of Health 2005). It is therefore essential to understand the activity patterns of these at risk individuals, in order to appropriately target public health initiatives. Physical activity levels tend to fluctuate according to season, being characteristically highest during the summer and lowest during the winter. This seasonal pattern has been well defined in large scale self-report studies, which have examined changes in leisure-time, occupational and household activity, in the USA (Dannenberg et al. 1989; CDC 1997; Matthews et al. 2001; Pivarnik et al. 2003) and UK (Uitenbroek 1993). Self-report measures of physical activity can however lack validity in that individuals often exhibit an inability to accurately self-assess low intensity activities, such as walking behaviour (Sallis and Saelens 2000). This may have implications for the use of self-report measures in sedentary societies. Walking is reportedly the most prevalent form of physical activity in both US (Simpson et al. 2003) and UK adults (Chief Medical Officer 2004). However, walking is commonly underestimated through questionnaires (Ainsworth et al. 1993; Richardson et al. 1994; Bassett et al. 2000). By not capturing walking, or ambulatory, behaviour adequately, self-report studies may lack the sensitivity needed to detect the actual seasonal physical activity experience of many individuals. Pedometers are rapidly gaining popularity in the research domain. The combination of their low cost, small size, simplicity and unobtrusive nature make them practical tools for objectively monitoring ambulatory activity in the free-living environment. Although accurate in measuring steps (Bassett et al. 1996), pedometers are not designed to capture short-term patterns in activity (<24 hours), intensity, or type of exercise (Tudor-Locke et al. 2002). The standardised steps per day unit of measurement enjoys universal interpretation, facilitating reliable cross-population comparisons. This type of comparison is often limited when using subjective measures (Lamb and Brodie 1990). However, despite the potential for pedometers to measure activity, to date there is limited data available describing the seasonal patterns in ambulatory activity of healthy free-living adults. Previous studies that have objectively assessed seasonal variability in ambulatory activity have been limited by either gender and duration (Lee et al. 1987), study aim (Chan et al. 2006) or sample size (Tudor-Locke et al. 2004a). Lee et al. (1987) compared summer and winter pedometer data collected in Kentucky, from 130 females aged 51 to 86 years, over two seasonally separate seven day monitoring frames. A significant summer to winter reduction in steps was reported in the form of distance walked. Chan et al. (2006) conducted a pedometer-based intervention with the aim to raise activity levels in Canadian adults (n = 203). Step count data were collected from two groups of participants, data from one group were collected between the months of March and July, and data from the second group were collected between December and April. Although a seasonal change in step counts was observed, the study aim was to increase walking activity and therefore it is unlikely that habitual levels were captured. Tudor-Locke et al. (2004a) assessed daily step counts reported over a continuous 365 day period in 23 US male and female adults. Although this preliminary study indicated a winter reduction in steps, the authors acknowledge the need for research to be conducted in a larger sample to confirm their findings. All research to date investigating seasonal changes in ambulatory activity (outlined above) has focused exclusively on North American populations, and very little research has been published investigating pedometer-determined activity in healthy, free-living UK adults. From the research available, using pedometers in UK adults, Clemes et al. (2007; 2008a) reported that mean daily step counts, measured in normal-weight, overweight and obese UK adults were higher, by approximately 3000 steps/day, than those observed in US adults. This suggests that there are potentially differences in activity levels between UK and US adults. No research has yet investigated seasonal changes in ambulatory activity of UK adults. Seasonal changes in physical activity are thought to be mediated through changes in the environment, with ambient temperature, daylight hours and precipitation considered most influential (CDC 1997; Merrill et al. 2005). Due to the diverse global climate, assessment and interpretation of seasonal patterns in ambulatory activity may vary between countries, and regionally specific studies are necessary to understand global patterns. For example, the climate in the UK is very different to the climate in the US. Climate data collected over a 30 year period in the UK show that minimum and maximum temperatures during summer and winter range between 10.3C to 19.9C (summer) and 1.0C to 6.7C (winter), respectively (Met Office, 2006). In contrast, climate data collected over the same time period from the state of South Carolina (one of the two locations used in the study by Tudor-Locke et al. (2004a)) show minimum and maximum temperatures between 21.8C to 31.6C and 4.1C to 15.6C in summer and winter respectively (Met Office, 2006). Given the number of sedentary adults and the rising problem of obesity in the UK, it is important to understand seasonal physical activity patterns of UK adults in order to develop appropriate public health initiatives. The aim of the current study therefore was to measure the seasonal variation in ambulatory activity of free-living UK adults, by comparing pedometer determined activity levels, collected over the summer and winter months. Methods Experimental design A within-subjects repeated measures design was employed, which consisted of two methodologically identical data collection periods. The first period of data collection took place during the summer of 2005, between the 21 June and the 22 September. The data collected during this time period has been reported elsewhere (Clemes et al. 2007). Participants were recalled and requested to repeat the ‘summer’ study during the following winter. The winter data collection period took place between the 20 January 2006 and 21 March 2006. This paper details exclusively those participants who completed both the summer and winter monitoring periods (n = 96).