"Healthiest You Ever: 365 Ways to Lose Weight, Build Strength, Boost Your BMI, Lower Your Blood Pressure, Increase Your Stamina, Improve Your Cholesterol Levels, and Energize from Head to Toe!" by Meera Lester, p. 291, December 18, 2011.
"Light on Life: The Yoga Journey to Wholeness, Inner Peace, and Ultimate Freedom". Book by B.K.S. Iyengar, John J. Evans and Douglas Abrams, p. 9-10, 2006.