Loss of hip extension range of motion is a common problem we see in PT. This can be related to symptoms in the lower back, hips, knees or ankles. Modern lifestyles can contribute to this problem. Hours spent in a seated position and decreased use of the gluteus muscles are two common things people who have restricted hip extension often share.
A simple exercise with some pertinent cues can help increase hip extension range of motion. The bridge is a common therapeutic exercise, however when performed in a specific manner can facilitate greater hip mobility.
Start in hooklying position, which is flat on your back with your knees bent and feet flat on the floor. Before movement begins, drive your heels into the ground. Visualize trying to drag your heels towards your butt. Next think of moving your knees forward (opposite direction of your heels) as you lift your butt off the floor. Hold this position for 2-3 minutes if possible with good form. Continue performing the cues mentioned as you hold your bridge.
Once in this bridge position, you can also straighten the uninvolved leg if your hip extension is limited only on one side.
Doing this on a daily basis will facilitate your posterior chain of muscles and result in improved functional hip extension. As always, stop if there is any pain and consult your MD or PT.