# Acute Effects of Midsole Bending Stiffness on Lower Extremity Biomechanics during Layout Jumps
## 4 Discussion
### Performance  
A contradictory result was observed in our study. In our results, the jump height of LJs did not improve with SS, which was contrary to our hypothesis that a stiff midsole in MTP would enhance performance. This observation is inconsistent with the performance improvement mechanism of decrease absorbed energy by SS. [PERSON] et al. (2019) claimed that MTP absorbs approximately 24 J during the push-off phase, which could theoretically improve the jump height of a mass body (70 kg) by approximately 3.5 cm. This phenomenon may be caused by the failure of SS to modulate the net energy of the lower extremities during LJs. In our study, only the absorbed energy, generated energy, and ROM of the ankle joint significantly changed, but the net energy remained the same (Table 4); this may be explained that the SS increased the ROM of the ankle joint. The increased ROM simultaneously improved the absorbed energy and the generated energy in the ankle, which resulted in no significant change in net energy in the ankle. Similarly, [PERSON] et al. (2018) investigated the effect of stiff midsoles on the mechanical energy of the lower extremities; their results indicated no significant difference. [PERSON] et al. (2019) suggested that SS did not change the take-off velocity of the center of mass while running. Therefore, SS did not alter the net energy of the lower extremities and did not increase the jump height of LJs.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Joint** & **Variables** & **SS** & **CS** & **Effect Size** & **P** \\ \hline \multirow{6}{*}{Hip} & Max. torque (N-m) & 98.4 (32.8) & 94.5 (31.7) & 0.121 & 0.729 \\  & Min. torque (N-m) & \(-\)612.7 (162.1) & \(-\)613.1(151.4) & 0.003 & 0.994 \\  & Min. power (W) & \multirow{2}{*}{1379.7 (776.3)} & \multirow{2}{*}{1551.4 (765.4)} & \multirow{2}{*}{0.223} & \multirow{2}{*}{0.407} \\  & Max. power (W) & & & & \\  & EA (J) & 21.8 (15.2) & 18.5 (12.4) & 0.238 & 0.495 \\  & EG (J) & 93.6 (25.6) & 100.9 (27.5) & 0.275 & 0.484 \\  & Net energy (J) & 71.8 (33.9) & 82.4 (35.2) & 0.307 & 0.447 \\ \hline \multirow{6}{*}{Knee} & Max. torque (N-m) & 273.1 (44.7) & 266.3 (38.1) & 0.164 & 0.515 \\  & Min. torque (N-m) & \(-\)150.1 (56.5) & \(-\)156.0 (61.7) & 0.100 & 0.756 \\  & Min. power (W) & \(-\)552.5 (209.5) & \(-\)564.1 (169.2) & 0.061 & 0.861 \\  & Max. power (W) & 1261.4 (305.1) & 1211.1 (265.9) & 0.176 & 0.492 \\  & EA (J) & 38.5 (13.5) & 35.5 (13.6) & 0.221 & 0.445 \\  & EG (J) & 78.9 (27.1) & 71.4 (28.1) & 0.272 & 0.260 \\  & Net energy (J) & 40.4 (17.6) & 35.9 (25.3) & 0.206 & 0.458 \\ \hline \multirow{6}{*}{Ankle} & Max. torque (N-m) & 19.7 (12.1) & 19.7 (9.8) & 0.000 & 0.977 \\  & Min. torque (N-m) & \(-\)301.3 (51.9) & \(-\)291.7 (33.5) & 0.220 & 0.365 \\ \cline{1-1}  & Min. power (W) & \(-\)557.6 (212.9) & \(-\)474.9 (180.5) & 0.419 & 0.122 \\ \cline{1-1}  & Max. power (W) * & 1359.6 (249.7) & 1191.7 (283.9) & 0.628 & 0.033 \\ \cline{1-1}  & EA (J) * & 39.1 (11.5) & 32.4 (10.4) & 0.611 & 0.028 \\ \cline{1-1}  & EG (J) * & 84.5 (18.6) & 70.9 (19.5) & 0.714 & 0.012 \\ \cline{1-1}  & Net energy (J) & 45.4 (19.3) & 38.5 (17.8) & 0.372 & 0.211 \\ \hline \hline \end{tabular} Note: SS, stiff midsole shoes; CS, control shoes; LJ, layup jump; Max., maximum; Min., minimum.; EA, energy absorbed; EG, energy generated. * Significant difference between shoes (\(p<0.05\)).  
\end{table}
Table 4: Hip, knee and, ankle joint kinetics during LJs (n = 30, Mean (SD)).