# Biomechanical Analysis of Running in Shoes with Different Heel-to-Toe Drops
## 4 Discussion  
In the current study, the participants were tested in running shoes that varied only in terms of heel-to-toe drop, and the average running speed across all the participants was 4.0 \(\pm\) 0.2 m/s. Running in shoes with large drops increased the foot inclination angle at initial contact, decreased the vertical loading rate, increased the peak knee flexion angle and extension moment, and decreased the peak ankle version angle and moment during the standing phase. Thus, the heel-to-toe drop of the running shoes was a key factor influencing the running pattern and the loading of the lower extremity joints. \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & \multicolumn{4}{c}{**Heel-to-Toe Drop (mm)**} \\ \hline
**Variable** & **15** & **10** & **5** & **0** \\ \hline
**Knee joint** & & & & \\ Flexion angle at initial & 16.4 \(\pm\) 7.1 & 16.4 \(\pm\) 7.6 & 16.5 \(\pm\) 6.1 & 17.8 \(\pm\) 5.8 \\ contact (\({}^{\circ}\)) & 47.1 \(\pm\) 4.7 \({}^{\ast}\) & 47.2 \(\pm\) 4.6 \({}^{\ast}\) & 46.3 \(\pm\) 3.8 \({}^{\ast}\) & 44.5 \(\pm\) 4.2 \\ Peak flexion moment & 0.52 \(\pm\) 0.11 & 0.50 \(\pm\) 0.19 & 0.45 \(\pm\) 0.15 & 0.49 \(\pm\) 0.16 \\ Peak extension moment & & & & \\ (N\(\cdot\cdot\)m\(\cdot\)kg\({}^{-1}\)) & 2.98 \(\pm\) 0.51 \({}^{\ast}\) & 3.11 \(\pm\) 0.51 \({}^{\ast}\) & 2.91 \(\pm\) 0.54 & 2.70 \(\pm\) 0.69 \\ Peak abduction angle (\({}^{\circ}\)) & 1.3 \(\pm\) 2.2 & 0.8 \(\pm\) 2.6 & 0.7 \(\pm\) 3.8 & 2.0 \(\pm\) 3.3 \\ Peak abduction moment & & & & \\ (N\(\cdot\cdot\)m\(\cdot\)kg\({}^{-1}\)) & & & & \\
**Ankle joint** & & & & \\ Plantarflexion angle at initial & 2.1 \(\pm\) 6.3 & 2.1 \(\pm\) 6.7 & 2.5 \(\pm\) 6.4 & 1.4 \(\pm\) 7.3 \\ contact (\({}^{\circ}\)) & & & & \\ Peak plantar flexion angle (\({}^{\circ}\)) & 33.9 \(\pm\) 4.8 & 35.1 \(\pm\) 5.0 & 34.5 \(\pm\) 3.9 & 34.5 \(\pm\) 4.9 \\ Peak plantar flexion moment & 2.77 \(\pm\) 0.46 & 2.71 \(\pm\) 0.48 & 2.75 \(\pm\) 0.38 & 2.85 \(\pm\) 0.44 \\ (N\(\cdot\cdot\)m\(\cdot\)kg\({}^{-1}\)) & & & & \\ Peak dorsiflexion moment & & & & \\ (N\(\cdot\)m\(\cdot\)kg\({}^{-1}\)) & & & & \\ Peak version angle (\({}^{\circ}\)) & 0.2 \(\pm\) 2.7 \({}^{\ast}\) & 0.7 \(\pm\) 3.0 \({}^{\ast}\) & 1.2 \(\pm\) 3.0 & 3.0 \(\pm\) 2.8 \\ Peak version moment & & & & \\ (N\(\cdot\)m\(\cdot\)kg\({}^{-1}\)) & & & & \\ \hline \hline \end{tabular} Note: BW = body weight. \({}^{\ast}p\) < 0.017, significantly different from no heel-to-toe drop.  
\end{table} 
Table 2: Comparison of biomechanical data of the knee and ankle joints among the four shoe conditions. The results of the current study support our first hypothesis that the foot inclination angle at initial contact would be greater when running in shoes with large drops compared with running in shoes without a drop. Our results revealed that the foot inclination angle at initial contact was more than \(5.7^{\circ}\) larger when running in shoes with large drops compared with running in shoes without a drop. No significant differences in the knee flexion angle or ankle plantar flexion angle were detected at initial contact. The effect of shoes without a drop on the gait parameters was much less than that of minimalist shoes. Runners struck the ground with less ankle dorsiflexion and more knee flexion [8] while running in minimalist shoes, which may be explained by features of the minimalist shoes other than drop. A previous study also found a positive correlation between the drop and foot inclination angle at initial contact for rearfoot runners [17]. With the increase in the foot inclination angle at initial contact, the knee joint's function as an energy absorber was increased [23]. When running in shoes with large drops, runners attempted to contact the ground with the rearfoot at initial contact, which placed the supporting leg further beneath the center of the body mass, thus increasing the quadriceps muscles arm and the knee extension moments [24; 25].