In humans, BMR is directly proportional to a person's lean body mass. In other words, the more lean body mass a person has, the higher their BMR; but BMR is also affected by acute illnesses and increases with conditions like burns, fractures, infections, fevers, etc. In menstruating females, BMR varies to some extent with the phases of their menstrual cycle. Due to the increase in progesterone, BMR rises at the start of the luteal phase and stays at its highest until this phase ends. There are different findings in research how much of an increase usually occurs. Small sample, early studies, found various figures, such as; a 6% higher postovulatory sleep metabolism, a 7% to 15% higher 24 hour expenditure following ovulation, and an increase and a luteal phase BMR increase by up to 12%. A study by the American Society of Clinical Nutrition found that an experimental group of female volunteers had an 11.5% average increase in 24 hour energy expenditure in the two weeks following ovulation, with a range of 8% to 16%. This group was measured via simultaneously direct and indirect calorimetry and had standardized daily meals and sedentary schedule in order to prevent the increase from being manipulated by change in food intake or activity level. A 2011 study conducted by the Mandya Institute of Medical Sciences found that during a woman's follicular phase and menstrual cycle is no significant difference in BMR, however the calories burned per hour is significantly higher, up to 18%, during the luteal phase. Increased state anxiety (stress level) also temporarily increased BMR.