When designing a fitness routine that is intended to muscles gain strength and size, what must you consider?

Muscles need a day or two of rest to refuel and repair

Explanation:

When the fitness routine of the body is designed then it should be designed in a way that body should get proper rest.

This is because the muscles of the body needs a day or two for its repair. It needs to be refueled in order to work again.

The work out sessions should not be daily. The body must get a rest of day or two to keep the muscles working well.