For most people, running is a very rough exercise on their bodies. The feet, knees, hips and spine absorb forces that equate to anywhere from 2-4 times their bodyweight. There are two things you can do to minimize these impact forces. One is to weigh less. The other is to improve your running biomechanics, so your leg muscles 'manage' or dissipate the forces more effectively.
Check out the runner in the above picture. He is not doing a good job dissipating forces. In fact, you can see his body weight is about to 'fall' directly on top of his foot with the impending heelstrike. This is usually followed by a 'pushing' leg action. Not good, but very common. Contrast this runner with the next picture.
The runners in the second photo are leaning forward more and 'pulling' their stance leg through. You will also notice the greater hip mobility and extension of the stance leg (compare back legs). The leg swinging through will land behind the runner's center of gravity more so with the second style of running, resulting in lower impact forces.
The last picture shows the difference in ground reaction forces (impact) with heel striking and forefoot striking. The 'pulling' style is associated with more forefoot striking, while the 'pushing' style is associated with more heel striking.
Identifying your running biomechanics are easy. Changing your style is more challenging. It involves changing several physical attributes, including hip and ankle mobility, hip strength and power, and motor coordination. When I work with a client who is trying to improve her running biomechanics, I utilize a variety of drills/exercises to improve mobility and increase hip 'pulling'. It is a gradual process that needs to be 'practiced' without undue fatigue.