As you run the greatest impact is experienced just after the foot first contacts the ground at the front of the stride. The degree of impact depends on:
- How far your foot contacts the ground in front of your hips
- The amount of tension held in the leg and foot
The further your foot contacts the ground in front of your hips, the further you place your leg in front of your body weight and the greater the time spent running into the leg rather than over it. The more you run into your leg the greater the impact, especially if the leg and its foot are tensed.
Running into the leg also wastes energy since it causes a loss of forward momentum as if you are momentarily putting on the brakes.