backbone, strength

膂 is composed of 旅 (travel) and the radical of 肉 (flesh). 旅 means traveling far from home, while 肉 refers to the human body. In ancient times, without the aid of machines, people traveling long distances had to carry their luggage by human strength. Those who carried heavy loads needed strong spinal bones. Therefore, 膂 is used to mean the spine or physical strength.