The interaction of fatigue and adaptability with lower extremity functional performance tests: Integrating neurocognition to evaluate adaptability

Functional performance tests are utilized by clinicians and researchers to compile injury risk profiles, monitor rehabilitation progress and to inform a criteria-based and safe return to sport decision-making approach. Functional performance tests are measurements that evaluate an athlete’s current functional ability. Although literature documents a significant association between some functional performance test outcomes and an increased injury risk, these tests should be interpreted in a more complex, athlete centered approach of sports injuries. In a comprehensive athlete centered approach, functional performance tests should also approximate the athletic context. This highlights the need to continuously develop functional performance tests and evaluate different interactions that arise within the athletic context. Interestingly, the current functional performance test approach neglect the relevance of fatigue and adaptability. Adaptability is defined as the athlete’s ability to modify responses under a broad spectrum of conditions. Fatigue is a multidimensional phenomenon and includes both central and peripheral fatigue mechanisms as well as physical and mental fatigue constructs. The goal of the present dissertation is to gain more insight in how fatigue interacts with functional performance tests, injury risk and adaptability. In our first study (chapter two) we provide a systematic literature review to identify the existing body of evidence on the interaction between acute physical fatigue and prospectively determined injury risk factors for lower extremity injuries. The body of evidence is scarce and of low quality, with no evidence that acute fatigue increases the non-contact ACL, ITBFS or generic lower extremity injury risk profiles. Only limited evidence was found for the statement that acute fatigue negatively affects the lateral ankle sprain, patellofemoral pain syndrome or hamstring injury risk profiles. In chapter three, we describe the systematic development and test protocol of the reactive balance test. The reactive balance test is a neurocognitive single-leg balance test that integrates environmental perception, decision making and reaction time. The outcomes are accuracy and visuomotor response time. The reactive balance test is a functional performance test that allows clinicians to score an athlete’s adaptability. Consequently, we performed two randomized cross-over studies to explore the effect of mental fatigue (chapter four) and acute physical fatigue (chapter five) with four functional performance tests, including three traditional functional performance tests, the Y-balance test, the countermovement jump test, the single leg hop test and the neurocognitive reactive balance test. The results presented in chapter four illustrate that mental fatigue does not affect outcomes of the included traditional functional performance tests, but does impair accuracy in the reactive balance test. Following a 90 minute 100% incongruent Stroop task, participants accuracy significantly decreased in the reactive balance test. Mental fatigue can negatively affect adaptability. The results presented in chapter five illustrate that acute physical fatigue can cause divergent fatigue responses in functional performance test outcomes. While the countermovement jump and Y balance test performance remained unaffected, single leg hop distance significantly decreased following a 30 second all-out sprint effort (Modified Wingate procedure). Acute physical fatigue also impairs accuracy in the reactive balance test and can also negatively affect adaptability. This thesis highlights that acute physical fatigue interacts with functional performance tests, but comprises large intra- and interindividual differences. Clinicians should be aware of this interaction and a paradigm shift is needed towards evaluating individual fatigue responses. Moreover, neurocognitive functional performance test can complement the current use of functional performance tests. For future research, more teamwork is needed to merge insights from fatigue and injury prevention experts. Additionally, evaluating individual fatigue responses might expose patterns that are masked in current data monitoring strategies and group-level analyses. Prospective research is needed to explore the added value of neurocognitive functional performance tests.