If someone is muscly, they have big, strong muscles.
Being muscly can make people think of strength, hard work, or being healthy.
Examples:
He is very muscly and can lift heavy things.
The muscly man can run very fast.
She became muscly after exercising a lot.
The muscly dog pulled the cart with all the kids in it.
The muscly superhero can lift a car with one hand.
The muscly wrestler won the match easily.