Strength: Power and explosiveness
Vitality: Endurance, immune system, regeneration, and total health
Dexterity: Flexibility, speed, and reflexes
Wisdom: MP regeneration, senses, and awareness
Intelligence: Total MP, memory, and ability to grasp complex thoughts
This will be a reactive system where the body changes based on the system.
I accidentally made this a real chapter. Let me know in comments if you want anything more seriously explained.