Tracking Fatigue with Subjective Scales in Soccer Referees

INTRODUCTION: Fatigue can have a negative impact on performance, especially when it is not adequately monitored and there is not an appropriate workload to rest ratio [1]. This could result in non-functional overreaching and overtraining not only in players, but also in referees. Therefore, the aim of this study was to investigate the relationship between Hooper index (HI) taken before training session and rate of perceived exertion (RPE) after a submaximal standardized warm-up in soccer referees. METHODS: After providing their written consent to participate in the study, 23 male referees from the Italian 4th and 5th divisions were followed during two months' soccer pre-season for a total of 244 training sessions. On average, each referee performed 11 trainings (min = 5; max = 24) with a standardized 10-min running warm-up (%heart rate max = 66±9%). Before all training sessions HI was administered [2], while at the end of the warm-up RPE was measured using the Borg category-ratio-10 scale. Intraclass correlation (ICC) was used to assess the internal consistency of the HI and RPE across the first five repeated standard warm-up sessions. High α coefficient (≥0.60) suggests good internal consistency and reliability. Relationship between HI and RPE responses were analyzed via linear mixed model (LMM) using HI and RPE as fixed effects, while the subjects' individual warm-up response as random effects. R-squared (R2) was calculated and Likelihood-ratio test was used to compare the LMM with the linear regression analysis. Significance level was set at 0.05. RESULTS: The ICC of HI and RPE across the first five repeated training sessions were 0.80 and 0.69, respectively, thus demonstrating good internal consistency. LMM (p<0.0001; Wald chi2=206.62; R2=0.48) had an estimated standard deviation for the random intercepts of 1.61AU (95%CI: 1.18-2.21) with standard error of 0.26. Likelihood-ratio test showed that LMM offered a significant (Chi2:132.59; p<0.0001) improvement over a linear regression, meaning the intercepts were significantly different between subjects. The relationship between RPE and HI, combining the fixed and random intercepts, can be expressed with the following equation: HI = 7.080777 + 1.336215*RPE + U0j + ɛi CONCLUSION: Results from this study demonstrate that HI and RPE values are directly proportional during a standardized submaximal warm-up in soccer referees. This could indicate that HI and RPE could be valid and practical tools to investigate non-functional fatigue during submaximal warm-ups. Findings from the present study can be used to tailor the workload during period of training and conditioning to avoid non-functional overreaching or overtraining. REFERENCES: 1. Haddad M et al (2013). Influence of fatigue, stress, muscle soreness and sleep on perceived exertion during submaximal effort. Physiology & Behavior, 119, 185-189 2. Hooper SL & Mackinnon LT (1995). Monitoring overtraining in athletes. Sports Medicine, 20(5), 321-327