Ostriches are the largest two-footed bird. While they are unable to fly, they are the fastest running birds in the world, reaching speeds of up to 43 mph. But how are these large birds able to reach such fast speeds? Understanding the kinematics of ostrich motion compared to humans can reveal to us important information that can help when designing human-based technologies.
In an ostrich’s movement, elastic energy is stored in the toe – not the achilles like humans. While studying three-dimensional joint alignment, Rubenson et al. found the ankle remains static during stance, meaning the energy storage actually occurs at the toe (d) joint instead of the ankle. When they plant their feet and drive forward, ostriches store elasticity and release energy in their toe joints. As the ankle (c) remains stable, the toe joint shows pronounced bending during stance, then recoils powerfully as the ostrich pushes off. The toe joint springs the ostrich forward through long, energy storing tendons, allowing efficient high-speed escapes from predators. Studying this biomechanical advantage is beneficial for humans, who are infamously known for overabundant energy storage in the achilles.
Another aspect of the ostrich is its unusual knee bend. The orientation of the knee as the ostrich runs appears to bend the ankle more backwards compared to humans. The knee flexes and simultaneously moves the lower leg inward and outward. This easily allows the swinging leg to clear the stance leg because the orientation of the swinging lower leg is inherently reaching out forward. In their later study, Rubenson et al. emphasize that the large knee flexion and extension helps to build lateral motion and stability. Automatic limb clearance during running, simplified joint control and enhanced stability all enable an ostrich’s surprisingly fast leg movement.
In their research on muscle function during ostrich running, Rankin et al. discovered that knee extensors act more as brakes than primary power-producers, which differs inherently from humans. While humans use knees largely to generate power, ostriches use them to absorb energy during early stance rather than contributing large positive work. This takes stress off of the knee joint and increases stability. Rankin also found hip and hip-knee muscles were the ones providing the propulsive drive, while knee extensors were focused on decelerating limb segments or dissipating energy as the foot contacted the ground. Knee joint optimization helps to support an ostrich’s wide-ranging lifestyle, as they conserve energy while traversing expansive plains in search of food.
The unique biomechanics of an ostrich make it one of the most unassuming athletes in the animal kingdom. Ostriches are great natural examples of biomechanical optimization because of their high-speed, energy-efficient, stable running. Scientists are able to study the aforementioned joint mechanics to gain strategies that can help human technologies such as prosthetic limbs and bioinspired robots. Similarly, other areas of human performance are impacted such as sports science. Developments in ostrich research offer blueprints for training and injury prevention by focusing athletes more on tendon elasticity and efficient energy absorption.