If you don’t use it, you’ll lose it.
Your muscles will adapt to the repeated demand you place on them over time. Without that added demand, you will see no change to the tissue.
Essentially, you will find yourself at a physical plateau.
In order to become stronger, you need to present your muscles with consistent stimulus so that they can break down, rebuild and adapt to the increased demand.
Your muscles are designed to do what is required. If there is zero or minimal stimulus to your muscles they will shrink. This is known as muscle atrophy. People who lead a sedentary lifestyle can be at risk.