The health benefits of blue exercise in the UK
We use the term ‘Blue Exercise’ to refer to physical activity undertaken in and around outdoor ‘natural’ aquatic environments such as lakes, rivers, canals and the coast (Depledge and Bird, 2009). These activities could involve being in the water (e.g. outdoor swimming/diving), on the water (e.g. sailing/canoeing), or simply by the water (e.g. walking along a canal tow-path). Given its popularity we also include recreational angling as a form of blue exercise. Although angling may seem to be associated with very little physical activity, energy expenditure estimates are similar to those for walking at a slow to moderate pace (Ainsworth et al., 2011). We do not, however, include swimming in man-made swimming pools, despite the fact that it is one of the most popular physical activities in the country with 13 per cent of men and 15 per cent of women reporting having been swimming within the past month (Stamatakis and Chaudhury, 2008). Although the motivations behind, and experiences of, such swimming are of interest and may promote positive outcomes (Barton et al., 2012) they are beyond the scope of the current chapter. Rather, consistent with the other chapters in this volume (as well as related articles, e.g. Pretty et al., 2005; Gladwell et al., 2013), our focus is on outdoor activities in natural, and in this case aquatic, environments.