The Effect of Knee Angle at Contact on Impacts While Running off a Raised Platform

Abstract

0418 Changes in the knee angle at contact will alter the impact forces and accelerations while running. These variables may influence the potential for overuse injury in runners. PURPOSE: The purpose of this research was to study the effects of changes in knee angle at contact on impact forces and accelerations while running off a 25 cm raised platform. METHODS: Five male and five female subjects (age: 25.3 ± 6.5 years; body mass: 68.6 ± 8.0 kg) completed ten trials in each of four conditions: (1) normal running, (2) normal running off a raised platform, (3) flexed knee running off a raised platform, and (4) extended knee running off a raised platform. Kinematic data were collected at 120 Hz using a Peak Motus motion capture system, ground reaction forces were collected at 3600 Hz using an AMTI force platform, and leg and head acceleration data were collected at 3600 Hz using PCB accelerometers. Subjects were required to maintain a self-selected pace during each trial (average speed: 2.7 ± 0.4 m/s). RESULTS: There were significant changes in knee contact angle between all conditions (17.0 ± 5.8 deg; 13.4 ± 5.1 deg; 20.4 ± 5.2 deg; 10.3 ± 4.4 deg respectively). Thus, subjects were able to voluntarily alter their knee angle at contact. Running off a raised platform significantly increased peak impact forces and extended knee running off the raised platform produced the greatest peak impact forces (1148 ± 133 N; 1825 ± 371 N; 1672 ± 504 N; 2111 ± 456 N respectively). All comparisons were significant except 2 vs 3. On the other hand, flexed knee running off the raised platform produced the greatest peak leg accelerations (7.4 ± 3.1 g; 13.7 ± 4.9 g; 16.1 ± 5.4 g; 13.3+5.2 g respectively). All comparisons were significant except 2 vs 4. Attenuation was significantly different for all comparisons (74.8 ± 10.4 %; 67.9 ± 12.2 %; 84.0 ± 7.1 %; 59.1 ± 14.0 % respectively). CONCLUSIONS: When subjects extend their knee at contact they increase their peak impact force without a corresponding increase in peak impact acceleration. This suggests that the mass that is being accelerated increases when the knee is extended during contact. This reduced the impact attenuation and may have increased the potential for injury to the musculoskeletal system. Further analysis will look at alterations to the internal forces in the body.