With every stride, a certain amount of force (ground reaction force) is transferred from the ground and up the leg as your body absorbs the impact to propel yourself forward. The more efficiently your body is at being able to absorb and transfer the ground reaction force, the longer it will take before your body fatigues. When you run however, your body absorbs a repeated impact force of 2-3 x’s your body weight with each stride. Therefore, it is very important to put your body in the best situation to absorb these forces when recovering from an injury. Minimizing downhill running during training can help reduce the amount of ground reaction forces your body has to absorb. High impact forces are associated with an increased occurrence of injuries. When running downhill with a -9 degree decline, impact forces have been shown to increase 108% compared to normal. Where as, running uphill at a incline of +9 degrees reduces impact forces by 65% compared to normal flat surfaces. So when training while recovering from an injury, avoid excessive downhill running and opt for flat routes that incorporate some uphill sections to minimize the impact forces. Additionally, soft surfaces such as gravel roads, hard-packed dirt trails, and low-cut grass fields can help absorb some of the impact forces with each stride. When running on the roads, use caution while opting for asphalt as it still has a little give to it and avoid concrete whenever possible. Appropriate training surfaces are key when trying to recover from an injury, so being attentive at trying to minimize impact forces will help create a more efficient and healthy training environment.

References:

Dixon, S. J., A. C. Collop, and M. E. Batt. Surface effects on ground reaction forces and lower extremity kinematics in running. Med. Sci. Sports Exerc., Vol. 32, No. 11, pp. 1919-1926, 2000.

Hardin, E. C., A. J. Van Den Bogert, and J. Hamill. Kinematic Adaptations during Running: Effects of Footwear, Surface, and Duration. Med. Sci. Sports Exerc., Vol. 36, No. 5, pp. 838-844, 2004.

Hreljac, A. Impact and Overuse Injuries in Runners. Med. Sci. Sports Exerc., Vol. 36, No. 5, pp. 845-849, 2004.