Use 'beefy' to describe someone with a strong physical presence that is immediately noticeable. The bodyguard had a beefy stature, deterring any troublemakers.
Pro Tip 2/3
Sporting Context
'Beefy' is often used in sports to describe players who are notably muscular and powerful. The new linebacker is really beefy, he's going to be a star next season.
Pro Tip 3/3
Casual Description
'Beefy' is typically informal when referring to muscle size; suited for casual conversation. Look at those beefy arms! Have you been lifting weights?