Hip extension is a movement pattern where the femur moves backwards relative to the pelvis from the sagittal view. This movement can be seen from the side of the individual where the angle between the femur and pelvis increases. Hip extension is a major part of many movements including the force producing parts of walking, running and cycling. Specifically, hip extension is controlled by the gluteal complex, mostly the gluteus maximus. The leverage gained from pushing the femur back is used to propel cyclists and runners have a similar capacity to use the glutes to push off. Hip extension is also a significant means of force production in standard movements like walking up a staircase, or as biomechanists would refer to it: a step up.
Observe the visualization of the hip extension. The knee may be locked or bent, but in most patterns the knee is bent to produce a combination of forces from both the knee and hip extensor muscles. This visualization shows a straight knee hip extension. Straight knee hip extensions can be used to isolate the glutes and prevent the quadricep muscles from contributing to force production.
One way to test this phenomenon is to lay on your stomach and lift your leg off the ground. Such a movement engages solely the glutes and can indicate an individual's capacity to use their glutes to produce a forceful hip extension. If you are not able to lift your femur off the ground behind you, then you likely have tightness in your hip flexor muscles or lack neural control of the glutes. Neural control refers to the capacity for the brain to engage muscles along the nervous system. Excessive sitting in hip flexion positions can reduce the neural control of the glutes in mostly sedentary individuals.