Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Master of Science in Kinesiology, Biophysical Studies



Major Advisor

Tyler N. Brown, Ph.D.


Shawn Simonson, Ph.D.


Tyler Whitmer


Introduction: Females are 4 to 6 times more likely to sustain an anterior cruciate ligament (ACL) injury than their male counterparts during running and cutting sports, such as soccer. This sex disparity is thought to result from altered lower limb neuromuscular control that females present when fatigued at the end of practice or games. Yet, current fatigue monitoring techniques typically vary in their reliability, applicability and efficiency. Purpose: The purpose of this study is to test the feasibility of the countermovement jump (CMJ) to quickly and reliably monitor fatigue in female soccer athletes. Methods: Twenty-two (age: 19.3 ± 1.1 yrs, ht: 1.7 ± 7.2 m, and wt: 61.9 ± 7.7 kg) females from an NCAA Division I soccer team had peak isokinetic strength and power and specific ground reaction metrics of a CMJ including: peak and rate of force/power development, impulse, and reactive strength index modified, quantified immediately before off-season training, and immediately prior to- and following the completion of the competitive season. Results: Quadriceps and hamstrings peak torque and average power increased following the competitive season for both limbs compared to pre-season and pre-training time points (all: p < 0.05). During the CMJ, maximum rate of power production and peak force were greater at the post-season compared to pre-training (p = 0.023 and p = 0.007, respectively) and pre-season (p = 0.024 and p = 0.044, respectively) time points, while peak power was greater at post-season compared to the pre-training (p = 0.018) time point. Changes in relative net impulse, peak power, peak landing force, and jump height during the CMJ demonstrated moderate to strong relations to changes in isokinetic variables from pre-training to post-season (all: p < 0.05, r > 0.4). Lastly, the same CMJ measures accurately identified 96% of starters (Eigenvalue = 2.147, p = 0.038) and 86% of first-year athletes, although the classification of first-year athletes was not statistically different than non-first-year athletes (Eigenvalue = 1.279, p = 0.173). Conclusion: The current research identifies the CMJ task as a promising tool for athletic trainers and sports performance coaches to reliably monitor female soccer performance in general, and training loads specifically. Immediately following the competitive season, the current athletes increased isokinetic strength and power as well as CMJ performance, with changes in CMJ performance exhibiting a significant relation to changes in isokinetic strength and power. Yet, following off-season training, where isokinetic strength and power declined, albeit insignificantly, a similar relation between changes in CMJ performance and isokinetic strength and power was not observed. The experimental outcomes may indicate that the CMJ task is better suited for identifying increases in strength and power rather than decrements and fatigue. These same CMJ measures may serve as an effective tool for identifying improved strength and power, and performance differences for specific members of a collegiate soccer team, as 96% of starters and 86% of first-year athletes were accurately identified.