# Patellar Tendon Force Differs Depending on Jump-Landing Tasks and Estimation Methods
## 4 Discussion  
The primary purpose of this investigation was to compare the patellar tendon force between landings of a vertical jump-landing (VJL) and a vertical jump-landing with a forward velocity component (FJL) in volleyball players. The findings of this study support \begin{table}
\begin{tabular}{l c c c c} \hline  & **Vertical** & **Forward** & **\(p\)-Values** & _Cohen’s d_ \\  & **Jump-Landing** & **Jump-Landing** & **\(p\)-Values** & _Cohen’s d_ \\ \hline Jump height (m) & 0.53 \(\pm\) 0.07 & 0.53 \(\pm\) 0.07 & 0.902 & / \\ \hline
**Peak quadriceps force (BW)** & 3.81 \(\pm\) 0.55 & 4.63 \(\pm\) 0.64 & \textless{0.001 }* & 0.969 (Large) \\ \hline
**Peak vertical GRF (BW)** & 2.73 \(\pm\) 0.78 & 3.64 \(\pm\) 0.89 & \textless{0.001 }* & 0.764 (Medium) \\ \hline
**Peak anteroposterior GRF (BW)** & 0.61 \(\pm\) 0.17 & 1.30 \(\pm\) 0.31 & \textless{0.001 }* & 1.940 (Large) \\ \hline
**Loading rate of peak vertical** & & & & \\
**GRF (BW/s)** & 67.71 \(\pm\) 59.95 & 167.42 \(\pm\) 91.23 & \textless{0.001 }* & 0.913 (Large) \\ \hline
**Peak knee extension moment** & & & & \\
**(Nm/kg)** & 1.98 \(\pm\) 0.31 & 2.44 \(\pm\) 0.39 & \textless{0.001 }* & 0.928 (Large) \\ \hline Ankle dorsiflexion angle at IC (\({}^{\circ}\)) & \(-\)25.5 \(\pm\) 10.0 & \(-\)26.8 \(\pm\) 7.8 & 0.266 & / \\ \hline
**Knee flexion angle at IC (\({}^{\circ}\))** & 23.1 \(\pm\) 5.4 & 25.5 \(\pm\) 4.4 & 0.033 * & 0.342 (Small) \\ \hline
**Hip flexion angle at IC (\({}^{\circ}\))** & 16.0 \(\pm\) 5.5 & 26.9 \(\pm\) 6.7 & \textless{0.001 }* & 1.226 (Large) \\ \hline Ankle dorsiflexion ROM (\({}^{\circ}\)) & 53.6 \(\pm\) 8.5 & 50.3 \(\pm\) 7.2 & 0.055 & / \\ \hline
**Knee flexion ROM (\({}^{\circ}\))** & 56.7 \(\pm\) 11.5 & 63.3 \(\pm\) 12.0 & \textless{0.001 }* & 0.397 (Small) \\ \hline Hip flexion ROM (\({}^{\circ}\)) & 35.1 \(\pm\) 16.5 & 35.4 \(\pm\) 15.1 & 0.804 & / \\ \hline \end{tabular} Notes: \(p\)-values as revealed by paired \(t\)-tests, \({}^{\ast}\)\(p\)-value < 0.05.  
\end{table} 
Table 2: Mean \(\pm\) standard deviation of kinetic and kinematic parameters for volleyball players during vertical and forward jump-landings. IC: Initial contact, ROM: range of motion. Figure 3: Mean and standard deviation time series graphs of the patellar tendon force estimated with inverse dynamic method (**A**) and static optimization method (**B**), the net knee extension moment (**C**), and the quadriceps force (**D**) for all participants during vertical jump-landing (dark grey) and forward jump-landing (light grey). our hypothesis that the FJL would generate higher PTF peaks and higher PTF loading rates compared to the VJL. PTF were on average 25% and 17% higher during FJL calculated with inverse dynamic and static optimization methods, respectively. According to the inverse dynamic method, FJL and VJL exposed the patellar tendon to an average maximal force of 5.0 \(\pm\) 0.8 and 4.0 \(\pm\) 0.6 BW respectively, which closely matched the results from previous investigations on lateral stop-jump, and the horizontal and vertical landing phases of a stop-jump [8,9]. Average PTF loading rates estimated with the inverse dynamic method were 57 \(\pm\) 14 and 33 \(\pm\) 7 BW/s on FJL and VJL, respectively, and were also in agreement with a previous investigation [8]. These findings confirmed that landing from a jump with a forward velocity component generated higher loads on the patellar tendon compared to landing from a jump with only vertical motion. In association with higher PTF, our results showed that participants landed with greater hip and knee flexion angles at initial contact and greater knee flexion range of motion during FJL compared to VJL. Inappropriate landing technique can influence the risk of patellar tendinopathy development [14]. For example, asymptomatic athletes with patellar tendon abnormality previously displayed greater knee flexion at initial contact during the horizontal landing phase of a stop-jump [30,31].