Secular trend represents a progressive tendency of changes in the consequtive generations, mostly observed in bodily development and maturation, during growth period or in adult sizes, and also in functional and psychological variables. The magnitude of the differences could depend on the genetic traits of the population and the environmental factors, especially on the level of socio-economical standards. Secular trend changes are characterized by decades, expressed e.g. in cm for body height, in kg for body weight, or month for menarcheal age, etc. to compare changes in different populations.