Analysis of information sources in references of the Wikipedia article "سرزندگی" in Persian language version.
According to this widely accepted model, at birth an individual was endowed with a finite amount of vitality. During childhood, the body used this vital energy for growth and activity. By adulthood, it did well to maintain its supply. With old age, however, the amount of vital energy was clearly in decline. The obvious result was the elderly individual's tendency toward increasing illness and general debility.
