# Changes in Joint Power and Energetics during a Sport-Specific Jumping Fatigue Protocol
## 1 Introduction  
Vertical jumping is integral to the performance of many sports, such as volleyball and basketball, requiring the coordination of the ankle, knee, and hip joints. While the ability to perform a single maximal effort jump is important, over the course of a basketball or volleyball game, an athlete may perform hundreds of jumps [1, 2], signifying the importance of an athlete's ability to maintain their vertical jumping performance for a prolonged duration.  
Fatigue is generally defined as a decrease in peak muscle tension and power output resulting in reduced work capacity [3]. As athletes become fatigued, changes in their movement patterns may occur [4], and increases in movement in the frontal plane during running fatigue have been reported [5]. With respect to vertical jumping, fatigue has been shown to reduce an athlete's vertical jumping performance [6, 7, 8, 9]; however, little is known about the underlying changes in mechanics behind the degradation in jumping performance. Studies investigating changes in vertical jump height incorporate many different methods to render athletes fatigued. These methods include long-duration running [7], knee extensor fatigue [9], plantar flexor fatigue [6], continuous jumping protocols [8, 10, 11], and different jumping styles such as drop jumps [12] and squat jumps [13]. Each protocol is undoubtedly effective at achieving fatigue; however, none can be assured to fatigue the participant in the same manner as a sport with frequent jumping.  
[PERSON] et al. (2014) [14] performed a kinematic analysis of the lower extremities with a sport-specific jumping fatigue protocol in which athletes performed vertical jumps every 7 s until their performance could no longer be maintained. When comparing the athletes' vertical jumps prior to and following fatigue, increases in jump time and an increase in the thigh segment angle upon movement reversal were reported [14]. While these data providesome insight into the changes in the lower extremities that occur during sport-specific fatigue, mechanistically, it remains unclear how the ankle, knee, and hip joint were influenced throughout the fatiguing protocol. Further insight can be gained by reviewing studies that indicated that both knee and ankle power are decreased following continuous stretch-shortening cycle exercises using a sled apparatus [10; 11; 15]. However, this measurement device (the sled apparatus) imposes limitations on the hip joint, one of the main contributors to jumping performance. Additionally, sled pushing is more synonymous with continuous jumping, which does not equate to sport-specific jumping performance. During sport, delays between jumps occur, and alterations in the rest interval between jumps have been shown to postpone fatigue and change its source [16].  
Overall, kinematic and kinetic changes in the lower extremities will occur as an athlete becomes fatigued during vertical jumping. However, the specifics of these changes are unclear. No previous studies have quantified how the biomechanics of the ankle, knee, and hip joint change as an athlete becomes fatigued during a sport-specific fatiguing protocol. If the changes in the mechanics of the joints of the lower extremities during a sport-specific fatiguing protocol are better understood, targeted strength- and conditioning-training programs can focus on these joints to prolong athletic jumping performance and reduce the onset or detrimental impact of fatigue. Therefore, the purpose of this study was to quantify the influence of a sport-specific, vertical jumping fatigue protocol on the biomechanics of the ankle, knee, and hip joint.