# Changes in Joint Power and Energetics during a Sport-Specific Jumping Fatigue Protocol
## 4 Discussion  
The purpose of this study was to determine how the lower extremities' biomechanics were altered as the athletes became fatigued. When fatigued, the ankle and hip power and net joint energy were reduced, and the athletes attempted to compensate this loss through an increase in their knee joint power and net energy. At the ankle joint, from 1-80% of the jump-based fatiguing protocol, the athletes were able to maintain ankle joint power, with no changes in the ankle moment or ankle angular velocity at peak power. However, during the last phase of the jump protocol (81-100%), a reduction in ankle angular velocity occurred, which caused a decrease in peak ankle power. Interestingly, while ankle angular velocity decreased, participants were able to maintain a consistent ankle plantarflexion joint moment (both peak moment and \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Kinetic Variable** & **1–20\%** & **21–40\%** & **41–60\%** & **61–80\%** & **81–100\%** & **Fatigued Jumps** \\ \hline Jump Time (s) & 0.891 & **0.865 * & 0.875 & 0.893 & 0.891 & 0.867 \\ Vertical Ground Reaction Impulse (Ns) & 533 & 526 & 526 & 531 & 528 & **517 *** \\ Peak Ankle Plantarflexion Moment (Nm) & 170 & 171 & 172 & 174 & 173 & 173 \\ Peak Knee Extension Moment (Nm) & 153 & **158 * & 160 & 162 & 161 & 161 \\ Peak Hip Extension Moment (Nm) & 242 & 239 & 234 & **227 * & **216 * & 216 \\ Ankle Angular Impulse (Ns) & 56 & 56 & 56 & 57 & 57 & 57 \\ Knee Angular Impulse (Ns) & 48 & **50 * & 51 & 51 & 49 & 49 \\ Hip Angular Impulse (Ns) & 92 & 91 & 88 & 87 & 86 & 87 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Vertical ground reaction impulse, peak joint moments, and angular impulses during the fatigue protocol. Bolded asterisks represent a significant difference from the previous jump phase. Figure 4: Ankle, knee, and hip joint energy absorbed (**left**), energy generated (**center**), and net energy (**right**) during the different phases of the vertical jump fatigue protocol. Bolded asterisks represent a significant difference from the previous jump phase. moment at peak power). Although previous studies have shown reductions in the ankle joint's peak power and angular velocity during vertical jumping following a fatiguing protocol [8; 11], the influence of fatigue during countermovement, double-legged jumps on the ankle plantarflexion moment has not been previously reported. Research on single-legged hopping has reported a reduction in the ankle moment; however, this was following a fatigue-to-failure protocol of weighted knee extensions [20]. During a sport-specific jump fatigue protocol, it appears that athletes can maintain their ankle joint moment but are not able to maintain their ankle joint angular velocity. This result is similar to those found by [PERSON] et al. (2020) [21], where no significant difference in ankle joint moment was observed during a double-leg jump following a running-based fatiguing protocol. From a muscular perspective, while direct in vivo measurements were not taken, it has been shown that when fatigued, the activity of ATPase, enzymes that catalyze the decomposition of ATP into ADP and a free phosphate ion, is reduced [22; 23], which would decrease the rate of force production but allow for the muscle cross-bridges to stay attached longer to produce force. At the hip joint, similar peak power reductions in the ankle joint occurred; however, the decrease in hip power occurred much earlier during the jump fatigue protocol, becoming prominent at the 61-80% phase with a continued decrease until the final three fatigued jumps. While the peak hip moments athletes could attain were reduced, the participants were able to maintain the same magnitude of hip moment at peak power, with the reduction in hip power occurring due to a decrease in hip angular velocity. A previous study has shown a reduction in hip joint angular velocity following a fatiguing protocol; however, no significant decreases in peak power at the hip joint were reported [8].