Body image is a multidimensional construct including perceptions and attitudes about the body. While much evidence demonstrates that body image is related to physical activity behaviour, this research has typically investigated appearance aspects of body image, and primarily in adolescent and young adult populations. However, functional concerns about the body may be more relevant to physical activity. Initial research shows sport participation is linked to higher measures of functional body image in adolescent females. However, the relationship between functional measures of body image and physical activity remains relatively unexplored in other populations. The purpose of the present study was to examine the functional dimension of body image (functional investment, value, and satisfaction) in relation to physical activity across the lifespan in a diverse sample of men and women. Two-hundred-and-six women and 144 men between the ages of 18 and 85 years completed measures of body function and a self-report measure of physical activity. Regression analysis showed that gender, functional investment (i.e., the importance placed on body function), and satisfaction with function were significant predictors of moderate-vigorous physical activity, accounting for 16.2% of the variance in physical activity. The functional variables alone accounted for 7.9% of the variance in physical activity. These results suggest that physical activity may be one way to improve body image by helping people focus on what the body can do, rather than just what it looks like.