8.8K views · 92 reactions | Why are fast-twitch muscle fibers the secret to aging well? Because they’re the source of your power, agility, and bone density. As we age, losing these fibers leads to weakness and falls, marking the beginning of decline. Heavy lifting, sprinting, and explosive movement keep them alive. Train your fast-twitch fibers, and you’re not just staying strong, you’re staying young. | Mark Sisson | Facebook