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RESEARCH PRODUCT

EFFECTS OF STRIKING STRATEGY ON LOWER EXTREMITY LOADING DURING RUNNING

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Backround It is expected that every second runner has a running-related overuse injury each year. The knee joint and Achilles tendon are the most commonly injured sites covering both about one fifth of all running related injuries. 1 Runners can be categorized into rearfoot strikers, mid-foot strikers or forefoot strikers based on the landing strategy at the instant of initial ground contact. Forefoot or mid-foot striking has been shown to reduce impact peak and loading rate of the ground reaction force during early stance phase. 2 Furthermore, the finding of the recent study suggest that forefoot striking may potentially decrease the risk of running-related injuries. 3 However, the effect of runner9s foot striking pattern on the ankle and especially on the knee loading is poorly understood. Therefore, the purpose of this study was to examine whether runners with forefoot striking exhibit different lower limb loading profile than runners who use rearfoot strike pattern. Methods Nineteen female athletes with natural forefoot strike pattern and pair-matched females with rearfoot strike pattern (n=19) performed running analysis at 4 m/s. Kinematic (300Hz) and kinetic (1500Hz) data was recorded using Vicon motion analysis system. Inverse dynamics was used to calculate knee and ankle moments during stance phase of running and biomechanical model was then utilized to estimate patellofemoral stress and Achilles tendon force. Results Forefoot strikers demonstrated lower patellofemoral stress compared to heel strikers (11.1±2.9 vs. 13.0±2.8 Mpa; P=0.04). In addition, the knee frontal plane moment was lower in the forefoot strikers compared heel strikers (1.49±0.51 vs. 1.97±0.66 Nm/kg; P=0.015). At the ankle level, forefoot strikers exhibited higher Achilles tendon force (6.3±0.8 vs. 5.1±1.3 BW; P=0.002) compared to rearfoot strikers. Discussion Forefoot strikers demonstrate lower patellofemoral stress and frontal plane moment compared to runners with rearfoot strike pattern. This suggests that runners with forefoot strike pattern may have reduced risk of running-related knee injuries. However, parallel increase in Achilles tendon loading may alter forefoot striker into higher risk of ankle and foot injuries.