I agree, Veronica! Tree trunks come in a wide variety of sizes and shapes. There are slim, beautiful tree trunks, and at the other end there are sequoyas - all are strong and firm. If a guy tells a woman, knowing that she's a cyclist, that her legs are like tree trunks, I'd assume he meant her legs are strong and firm. That's a compliment to her athleticism and athletic figure.

Take it and run!

Deb