You try to eat right, you try to be more active, but your legs aren’t fitting into your jeans now any better than they were last month. What’s going on? Like what you’re reading? Then LIKE us on Facebook! Leg 101 The length of your legs is a matter of genetics. Studies show that, in general, the average 18- to 45-year-old woman’s legs (determined by crotch height) make up about 45 percent of her total height versus 44 percent for the average man in the same age group. Your leg muscles are another story – how they look depends both on your genes and your daily habits. We all have the same main leg muscles: the quadriceps, the hamstrings, and the adductors make up the thighs, the below-the-knee tibialis anteriors make up the shin muscles, and gastrocnemius and soleus muscles make up the calves. But there’s a wide range of sizes and muscle makeup among people that even experts debate. According to Daniel Lieberman, PhD, professor of human evolutionary biology at Harvard University, musclefibers in humans evolved so that most of us have legs with a majority of slow-twitch fibers, which give us our staying power during long runs. “We’re built more for endurance, whereas chimps have more fast-twitch fibers,” he explains.