The good news: "Every human has one," says Liles. It's actually formed by two ligaments that descend from the hip.
The bad news: "It isn't always visible. People who are naturally skinny may have theirs visible (lucky them)." In other words, one needs to be very trim, with a low body-fat percentage (roughly 5-8 percent, as reported by Men's Journal).
More good news: "There are steps that you can take to help make your own come out." Surprise, surprise: healthy diet and exercise.
How to Get an Inguinal Crease
1. High intensity interval training: Liles recommends doing "really challenging cardio" to boost your metabolism. "Keep in mind that fat burns proportionately around the body, so if you have a high deposit of fat in your midsection, that's likely going to take longer to go down enough to make it visible."
2. Ample core work: "To make your abs prominent think leg raises, toe-to-bars, trunk twists and oblique exercises to really shape out your midsection."
3. Eliminate starchy carbs and simple sugars: "Swap them out for complex carbs and fibrous vegetables. To give you just enough fuel to blast through your fat-loss training program. [Add] proteins to build muscle and healthy fats to satiate you and provide energy."