# Biomechanical Analysis of Running in Shoes with Different Heel-to-Toe Drops
## 4 Discussion
The results of the current study support our second hypothesis that the vertical loading rate would be lower when running in shoes with large drops compared with running in shoes without a drop. According to the traditional view, the cushioning structure of running shoes allows for more material deformation and lowers the impact force, thereby playing an important role in protection of the lower extremities during running. Another view is that running shoes with large drops would promote a rearfoot strike pattern that increases the impact force [26]. Several studies have shown mixed results for the effect of the drop of running shoes on the vertical impact force and the vertical loading rate [5; 8; 13; 14; 15; 27]. This disagreement is likely caused by the use of different brands and models of running shoes, which have different midsole construction designs and midsole materials. The results in our study suggest that the observed differences in previous research among shoes with respect to the vertical impact force may have stemmed from factors other than drop, such as the midsole geometry, midsole stiffness, midsole thickness, or shoe weight, and that the drop of running shoes was a key factor influencing the vertical loading rate. Our study compared running shoes that varied only in terms of the drop and showed that running in shoes with large drops did not change the vertical impact force but significantly decreased the vertical loading rate. Previous studies, in accordance with our study, have shown a decrease in the vertical loading rate when increasing the drop of running shoes or the foot inclination angle [7; 28]. At initial contact and during the early standing phase, ankle dorsiflexion was significantly weakened when running in shoes without a drop, suggesting the pre-activation of the plantarflexion muscles was greater. The higher vertical loading rate observed in shoes without a drop was in accordance with previous studies that showed a significant positive correlation between the amplitude of pre-activation of the gastrocnemius and the vertical impact peak [7; 29]. Combined with a previous study, the results of current study may have significance in preventing pathologies. The previous study showed that a higher body fat percentage, suggesting excessive loading and musculoskeletal pain, was associated with depression and poor health-related quality of life in an older population [30]. Considering that higher loading rates are associated with lower extremity injuries, it is recommended to wear running shoes with large drops to reduce lower extremity injuries, and this may improve the health-related quality of life. The results of the current study support our third hypothesis that the peak knee extension moment would be greater when running in shoes with large drops compared with running in shoes without a drop. Our results showed a greater knee flexion angle and extension moment during the middle standing phase when wearing shoes with large drops but no significant differences for the knee flexion angle at initial contact, which is consistent with the conclusions of a previous study. Higher knee extension moments may indicate greater activity of the quadriceps muscles, which can increase the force transmitted to the patellar tendon, strain around the patella, and patellofemoral stress [7]. Patellofemoralpain is a very common lower limb injury for runners [2]. Elevated patellofemoral stress is proposed as the direct cause or mechanism of patellofemoral pain, and patients with patellofemoral pain exhibit greater knee extension moments and patellofemoral stress than the pain-free controls [31; 32]. Our results suggest that running in shoes without a drop might minimize strain around the knee, which may have therapeutic benefits in reducing the risk of knee injuries and patellofemoral pain. Previous studies have demonstrated that barefoot running and running in minimalist shoes were associated with decreased knee moment and patellofemoral stress, respectively, compared with traditional running shoes.