| The world's most important pieces of infrastructure are overbuilt with safety in mind. New bridges can handle stresses far beyond what they'd ever experience, and airplanes are similarly designed with redundancies. But it turns out that this engineering principle is ripped straight from the biology playbook: The human body also has a few overengineered parts just to be safe. Nowhere is this more obvious than the femur, the body's largest bone, located between the hip and knee. The femur is more than up for its job, as it's capable of holding up to 30 times your body weight, or roughly 6,000 pounds (though the exact weight depends on the person and age). Named from the Latin for "thigh," the femur has many important functions beyond just holding your weight. The femur stabilizes you as you walk, connects muscles and tendons from your hips and knees to the rest of your body, and also plays a vital role in blood circulation via the femoral vein (named after the femur). Because the femur can withstand so much weight, fracturing the bone is usually only possible during extreme trauma events, such as a car crash. Breaking a femur can be particularly life-threatening because it can lead to blood clots, but luckily, most injuries can be repaired with surgery and physical therapy. So the next time you're struggling to backpack up a mountain or just carrying a heavy box up some stairs, don't worry — you're (over)built for this. | 
