Nestor Urrea

Date of Award

Spring 2023

Document Type

Open Access Thesis


Exercise Science

First Advisor

Shawn Arent


INTRODUCTION: Inter-limb functional asymmetries greater than 15% have been linked to a greater incidence of injury. Moreover, asymmetries greater than 10% have shown greater risk of injury and worsened sport performance, especially for strength and power capabilities, in athletes of multiple sports. Fatigue and sex are factors that seem to influence injury rates as well as greater asymmetries between limbs. This research project aims to investigate the effects of a fatiguing bout of exercise in strength and power inter-limb functional asymmetries in male and female soccer players. It was hypothesized that strength and power asymmetries are negatively affected after a treadmill-based simulated match protocol in male and female soccer players. It was also hypothesized that females will show more exacerbation of strength and power asymmetries compared to males.

METHODS: 38 high level soccer players (Males n =18; Females n =20) participated in an experimental study that consisted of two lab visits in a span of one week. Each participant executed strength and power performance tests pre and post a 90-minute simulated game treadmill protocol. Performance tests included a single-leg press, bilateral countermovement jump (CMJ), unilateral countermovement jump (SLCMJ), bilateral drop jump (DJ) and unilateral drop ump (SLDJ). All performance metrics were analyzed using a paired t-test pre vs post as well as for sex comparison analysis. Statistical significance was set at α=0.05.

RESULTS: Significant decreases in jump height were observed in CMJ, DJ, SLCMJ and SLDJ (P<0.05) as well as reduction in number of repetitions on the single-leg press (P<0.05). Male athletes showed greater significant decreases in performance in comparison to female athletes. In addition, significantly higher internal load was seen in males during the fatiguing protocol.

DISCUSSION: Fatigue negatively affected inter-limb functional asymmetries in high level soccer players, especially in male athletes. Sex differences in performance post intervention seem to be due the higher workload during treadmill protocol. More research is still needed to develop a standardized method to measure inter-limb asymmetries and its influence in sport performance and return to play protocols.

CONCLUSION: A 90-minute exercised-induced fatigue protocol that simulated soccer physical demands did negatively affect power and strength asymmetries in the lower limbs in high level soccer players. In terms of sex differences, men presented higher fatigue index which led to greater changes in inter-limb asymmetries for strength and power compared to women.