"In 1993, a British team measured the effects of three relaxation techniques: chair sitting, visualization, and yoga and found that yoga resulted in the greatest increase in alertness, mental and physical energy, and lust for life. Likewise, a 1994 German study, which compared a group of women practicing hatha yoga to a second group that did not, found that the yoginis showed markedly higher scores in life satisfaction, and lower scores in aggressiveness, emotionality, and sleep problems."Link