Centers for Disease Control and Prevention. How much physical activity do older adults need? Physical Activity for Everyone. http://www.cdc.gov/physicalactivity/everyone/guidelines/olderadults.html. Updated 6/2015. Accessed May 2016.
Centers for Disease Control and Prevention. Measuring Physical Activity Intensity. Physical Activity for Everyone. http://www.cdc.gov/physicalactivity/everyone/measuring/index.html. Updated 6/2015. Accessed May 2016.
Morey M. Physical activity and exercise in older adults.UpToDate http://www.uptodate.com/contents/physical-activity-and-exercise-in-older-adults. Last updated Sep 01, 2015. Accessed May 2016.