One of the most important measurements in nutritional assessment is body weight or body mass. Weight–height tables are convenient, quick, and easy to use. Another measure of weight for a given height is the body mass index (BMI), also known as the Quetelet index. Essential fat is stored in the bone marrow, heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues of the central nervous system. Storage fat is simply a depot for excess fat. Scientists have developed a variety of techniques to measure various body components including fat, protein, bone mineral, and body water. Most of the attention to body composition and its influence on health has focused on the proportion of body fat. Somatotype concerns physical types or physique of the body. Adding more fat to the body just to increase the athlete's weight and overall size is generally detrimental to performance. Hydrostatic weighing is a valid, reliable, and widely used technique to determine whole-body density.