The effect of fatigue on decision-making in amateur Rugby League players

Abstract

Introduction
Previous research in Rugby League has reported reductions in agility following game-specific exercise. A fundamental component of agility is decision-making as players are required to execute a quick change of direction in response to unpredictable stimuli (Serpell et al. 2010). Considering that the high physiological demands of the sport force players to compete in a fatigued state, the aim of the study was to examine the impact of match-related fatigue on decision-making, accounting for participant’s aerobic capacity.

Methods
Twelve Rugby League players (mean ± SD, age 22.9 ± 2.9 years, height 178.9 ± 9.3 m, body mass 87.7 ± 11.5 kg) participated in this study following ethics approval and informed consent. In the first session participants undertook measurements of anthropometry, fitness testing and an assessment of aerobic capacity (20 m Multi-stage Fitness Test (Ramsbottom et al. 1988)). During the second session participants were asked to perform an 80-minute match simulation protocol (Sykes et al. 2013) with the repeated Reactive Agility Test (rRAT; Jordan et al. 2013) performed at six time points throughout the simulation protocol.

Decision time, sprint time and total time were assessed using a two-way analysis of variance (ANOVA) with repeated measures (time point [6] x trial [3]) to assess their variability over time and between trials.

Measures of heart rate, ratings of perceived exertion and blood lactate and glucose concentration were also taken continuously throughout the protocol and were assessed using one-way repeated measures ANOVA.

The Pearson product moment correlation coefficient was used to determine the
relationship between RAT times and physiological variables (HR, RPE, BLa, blood
glucose) and between RAT times and physical qualities (agility, sprint speed).

Results
Decision time following the first half (RAT3) and following the second half (RAT5) did not significantly differ from baseline (F_{(2, 22)} = 5, P = 0.388, ^η2/p = 0.102). However, further analysis revealed that decision time immediately following cessation of exercise increased, as the time taken to complete the first trial of each rRAT was significantly higher than the time taken to complete the third trial (P = 0.027) across the six time points. Analysis was then performed again using individual aerobic capacity as covariate. No significant interaction was reported. There were no significant main effects on sprint and total time.

Mean blood lactate concentrations during the simulated protocol was 2.86 ± 0.54 mmol.l^-1, with concentrations following 1st half and following 2nd half being significantly higher than rest (P = 0.006 and P = 0.008, respectively). Mean heart rate reported was 152 ± 16.7 beats.min^-1, with values following RAT3 and RAT5 significantly different from RAT1 (P = 0.011 and P = 0.008, respectively). Similarly, ratings of perceived exertion following RAT3 and RAT5 significantly differed from RAT1 (P < 0.001 and P < 0.001, respectively). In addition values following RAT2 and RAT6 were also significantly different from one another (P = 0.002). Blood glucose concentration levels at rest were 4.26 ± 1.20 mmol.l^-1 and remained elevated during the 1st half of the game as well as half time (4.52 ± 1.68 mmol.l^-1), and then decreased during the 2nd half (3.99 ± 1.66 mmol.l^-1), values did not significantly change (P > 0.05) however, during the simulated game.
DiscussionThe current findings that decision-making time increased following periods of rugby league-specific exercise, but not over time, may suggest that there is only an acute effect of match-related fatigue on decision-making and not a cumulative. As decision time is comprised of both perceptual processes and peripheral events, the findings cannot be explained by a single mechanism. 

Date of Award	2015
Original language	English
Awarding Institution	Coventry University
Supervisor	Jo Hankey (Supervisor), Michael Duncan (Supervisor) & Mark Lyons (Supervisor)