Final answer:
Irregular periods and Amenorrhea fall under the c) Menstrual Function category of the Female Athlete Triad, which relates to menstrual cycle irregularities in athletic women.
Step-by-step explanation:
The category of the Female Athlete Triad to which irregular periods (Amenorrhea) belong is c) Menstrual Function. The Female Athlete Triad is a condition often observed in athletic women and consists of three interrelated components: low energy availability (with or without an eating disorder), impaired bone health (osteoporosis or osteopenia), and menstrual dysfunction (amenorrhea or oligomenorrhea). Irregular periods or an absence of periods (amenorrhea) directly fall under the menstrual function component. Conditions such as polycystic ovary syndrome (PCOS) can also affect menstrual regularity and are part of a broader discussion about hormonal health and menstrual cycles.