Background A lot of controversy exists about how fatigue affects injury risk. Within the fatigue spectrum, mental fatigue impairs visuomotor skills, reaction time and decision-making. Recently, adaptability has been put forward as an important driver in understanding injury occurrence and injury prevention. It is hypothesised that mental fatigue decreases an athlete’s adaptability by means of an increased visuomotor reaction time and diminished ability for decision-making and visuomotor skill execution.

Objective To assess the impact of mental fatigue on functional tests used in injury risk profiling and if mental fatigue decreases an athlete adaptability.

Design Randomized counterbalanced cross-over design.

Setting Primary prevention.

Participants Fourteen healthy participants (age = 22 ± 1 years; height = 176.9 ± 8.4 cm; weight = 69.7 ± 10.4 kg).

Interventions Mental fatigue was induced by a 90-minute 100% incongruent Stroop color word test, while the control task included watching a 90-minute documentary.

Main Outcome Measurements Y-balance test (YBT), Reactive balance test (RBT), Single leg hop test (SLH) and countermovement jump (CMJ) performance was evaluated pre-post mental fatigue. Mental fatigue was evaluated using the M-VAS, Stroop and Eriksen-Flanker task performance outcomes.

Results Mental fatigue was successfully induced at the subjective level with a significant increase in M-VAS (p<0.001), with no decrease in performance on the Stroop and Eriksen-Flanker task. Mental fatigue did not affect YBT, SLH and the CMJ performance. However, RBT accuracy significantly decreased in mental fatigue condition (p=0.024), while the visuomotor reaction time of the RBT remained unaffected.

Conclusions This is the first experiment to illustrate that mental fatigue affects functional adaptability, as accuracy in response to environmental stimuli decreases. However, traditional functional test perfmance remains unaffected. Therefore, both neurocognitive functional tests and mental fatigue responses should be considered within injury risk profiling strategies. Prospective study designs within the injury prevention domain should include neurocognitive functional tests to investigate the possible relationship of these tests with sports injuries.