Impact Forces In Running Injuries

GRF
Impact forces according to Messier et al. (1991) have been implicated in the risk of overuse running injuries along with active forces which can also have an important role in contributing to overuse running injuries. Impact forces can be defined as the force resulting from two bodies colliding over a period of time (Nigg et al., 1987 CITE). The graph below (Figure 2) represents vertical ground reaction force against time when running.

FIGURE 2 (Hreljac, 2004)

Impact forces usually are of a short duration and a relatively high magnitude. It is the first peak in the vertical ground reaction force curve during the first stage of the stance phase. Impact forces in landing or jumping activities can be more than 10-12 times bodyweight and last no longer than 10ms. Even in running, impact forces can range in magnitude from 1.5 to 5 times bodyweight. Cavanagh et al. (1980) also had similar results when undertaking a study that showed forces during running to be between 1.5 to 2 times bodyweight. Impact forces in running can last anything from 10ms to 30ms (Hreljac, 2004). Active forces which are the second peak in the vertical ground reaction force graph usually

(2002), it was found that females with a history of stress fractures showed greater peak impact forces, higher loading rates and a greater peak tibial acceleration than a group of control females who did not have a history of stress fractures. James et al. (1978) stated that the average runner could run up to 130km/week meaning the lower limb is subjected to approximately 40000 impacts over a weekly period. He also states that although a limb with normal alignment may withstand this type of repeated loading, an athlete with abnormal alignment, such as overpronation, can be a risk for developing an overuse running related injury. Soft tissue structures of the body such as muscles are adaptive to these forces and act to disperse forces as they move up along the