Final answer:
Humans have one of the longest pregnancy periods among mammals, involving significant changes in the mother's body and intense muscular work during labor and delivery.
Step-by-step explanation:
The question is asking about one of the longest periods in humans. The answer to this question is pregnancy. Humans have one of the longest pregnancy periods among mammals. During pregnancy, the mother's body undergoes significant changes in order to expel the baby at the end of pregnancy. The process of labor and delivery involves intense muscular work and is the result of a positive feedback system.