What does levelling a muscle give me?

Two things, and both belong to that one muscle.

• It earns more: that muscle earns more XP from the same work, up to 50 percent more at Level 20.
• It defends better: in a war, the XP someone needs to take a star off you goes up.

Those two rise by the same amount on purpose. If you and the person attacking you both level up, neither of you pulls ahead.

Levelling one muscle does nothing for your other muscles. Each one has its own Level and earns its own reward.

Learn more: How war stars work