Forty-eight male amateur long-distance runners were recruited. Two participants in the experimental treatment were excluded due to injury and premature exhaustion during the race. All participants signed a written, informed consent prior to participation. All procedures used were approved by the Ethics Committee from the University of Verona and were conducted in conformity with the Declaration of Helsinki.
Participants were recruited and tested over three editions (2015, 2016, 2017) of Run4Science. Run4Science is a competitive event (marathon and half-marathon) organised by the University of Verona (in collaboration with the Italian Athletics Federation and with the patronage of the city council) to give scientists the opportunity to study long-distance running in real-life conditions.
Subjects eligible for this study were involved in regular running (aerobic) training, free of any known disease, injury and medical treatment. In order to have a homogeneous fitness level, the recruited runners were first asked to complete a training-competition history questionnaire and a physical activity rating scale (PA-R) (Ross and Jackson 1991). Only those runners with a physical activity rating above 6 were included in the experiment.
Participants were not aware of the real aim and hypotheses of the experiment. They were told that the study aimed to investigate the effects of two different kinds of cognitive activities on physiological and psychological responses to a half-marathon race.
A between-subject, posttest-only, randomized controlled design was used for this pragmatic trial. Participants were randomly asked either to perform a 50-min mentally-fatiguing task immediately before the half-marathon (experimental treatment) or to read some magazines for the same amount of time, always prior to the competition (control treatment). To control for the potential confounding effects of atmospheric conditions and other variables that may differ between the three races, participants at each data collection constituted a separate block and were randomly allocated to treatment as follows. To create two groups of equal size and similar maximal oxygen consumption (V̇O2max) at baseline, random allocation to treatment was performed in blocks of two participants ranked according to their V̇O2max which was estimated using a validated multiple regression equation that takes into account subjects’ PA-R (Ross and Jackson 1991), Body Mass Index (BMI), gender and age (Jackson et al. 1990). Participants’ features (general and per group) are reported in Table 1. For statistical analysis, the three blocks of participants (one for each data collection) were pooled together.
The study took place at the Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona. Both psychological and cognitive task interventions were carried out in a standardised lecture room. The half-marathon race took place in proximity to the School (See Fig.1A and 1B for the course).
One week prior to the half-marathon, runners were familiarized with the use of the 100-point rating of perceived exertion (RPE) scale (Borg 1998) and other questionnaires/scales (see Psychological Questionnaires). They were also informed to drink around 35 ml of water per kg of body weight, to sleep at least 7 hours, to refrain from alcohol consumption and to avoid strenuous exercise within the 24 hours preceding the experiment. Participants were also asked not to consume any caffeine and nicotine for at least 3 hours before the experiment.
On the race day, after a standardised breakfast (07:00-07:30 am), subjects were divided into two groups and asked to sit down either in the front (mental fatigue) or the back (control) of the lecture room. The experiment started at 08:00 am.
Participants were required to complete a mental and a physical fatigue scale (see Psychological Questionnaires). They were then asked to perform either the mental fatigue or the control task for 50 minutes (see Treatment). Immediately after the task subjects were required to complete the same fatigue scales completed at baseline. In order to assess subjective workload perceived during the treatment, and motivation and expectations related to the half-marathon race, participants completed a workload-related multidimensional scale, a motivation questionnaire and an expectation scale, respectively (see Psychological Questionnaires).
After the treatment and the completion of the psychological questionnaires participants performed the half-marathon race (the ranges of atmospheric conditions during the three data collections were: temperature: 20.5-24.2 °C; humidity: 35%-53% RH; barometric pressure: 1013-1029 hPA). The course was a controlled 7-km circuit to be completed three times. The starting point was located inside the University outdoor track. Participants were equipped with a shoe race chip through which lap and overall performance times were taken. At the end of each lap athletes were required to run on the track and pass through the start, where RPE were collected. RPE was measured using the 100-point scale (Borg 1998). Two big posters of the same scale were placed in proximity of the starting point at 50-meter distance between each other. Subjects’ heart rate (HR) and running speed were continuously collected throughout the entire race using GPS watches (Polar V800, Polar Electro Oy, Kempele, Finland). Participants were asked to do a 10-min warm-up immediately before the race. Participants were free to drink ad libitum during the race.
At the end of the race participants were asked to go back to the lecture room and to complete the same physical and mental fatigue scales related to the half-marathon race (see Psychological Questionnaires).
In the mental fatigue group, treatment consisted in performing 50-min mentally-fatiguing tasks on a tablet screen (iPad Mini 2, Apple, California, USA). The mentally-fatiguing task was developed by Axon Sports (Phoenix, Arizona, USA), and consisted of five consecutive blocks of 10-mins, during which a simple response task and a search response task were run. In the simple response task participants were required to detect and press a visual stimulus (a green target) appearing randomly in the centre of the screen (stimulus frequency between 500 ms and 1500 ms). The total duration of the simple response task was 45 seconds per block. In the search response task participants were asked to detect and press a green target (go stimulus) and not to respond to a red target (no-go stimulus). Both stimuli appeared randomly in different positions on the screen (stimulus frequency between 750 ms and 1000 ms). A bleep sound was elicited in case of incorrect response. The total duration of the search response task was 9 minutes and 15 seconds per block. In the control group, treatment consisted in reading some magazines for 50 minutes, as it is considered a relaxing leisure activity (Kirsch and Guthrie 1984). Participants were continuously monitored by the researchers to guarantee compliance with both treatments.
Mental and Physical Fatigue
Two Visual Analogue Scales (VAS) were used to assess mental and physical fatigue before and after treatment. The VAS used was the same one present in the multidimensional scale NASA Task Load Index (TLX) (Hart and Staveland 1988). It consists of a 100-mm horizontal line divided into 20 half-centimetres intervals. Subjects were asked to circle one of the 20 line intervals based on their current feelings of physical or mental fatigue. The total range of scores is between 0 and 20. The line ends are anchored by descriptors defining the extreme feelings of fatigue: “no fatigued at all” and “extremely fatigued”. Before statistical analysis, change scores (score after treatment minus score before treatment) were calculated for both physical and mental fatigue.
The multidimensional scale NASA TLX (Hart and Staveland 1988) was used to estimate subjective workload that participants experienced during the treatment. The NASA TLX includes six subscales which determine workload: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort and Frustration. Subjects were asked to circle one of the 20 line intervals on each of the six scales at the point which matched their experience. Each line has two endpoint descriptors “very low” and “very high” that describe the scale. The performance-related subscale goes from “good” on the left to “poor” on the right.
Intrinsic motivation and success motivation scales (Matthews et al. 2001) were used to assess motivation related to the half-marathon race. Each scale includes 7 items to be scored on a 5-point Likert scale (where 0 = not at all, 1 = a little, 2 = somewhat, 3 = very much, 4 = extremely). The total range of scores for each scale is between 0 and 28.
The same VAS used in the NASA TLX was also adopted to measure participants’ expectations related to the half-marathon race. Subjects were asked to circle one of the 20 line intervals based on how well they expected to perform their race. The line ends are anchored by descriptors defining the extreme expectations: “much better than my personal best” and “much worse than my personal best”. A third descriptor “my personal best” was added to the centre of the VAS.
The Shapiro-Wilk test, histograms, Q-Q plots and boxplots were used to check all data for normality. If data were not normally distributed, non-parametric tests were used.
Independent t-tests were used to analyse between-group differences in motivation and expectation scales, and the change score of mental fatigue. Mann-Whitney tests were used to test between-group differences in the change score of physical fatigue and the workload scales referred to the treatment.
An independent t-test was used to analyse the between-group difference in the half-marathon time. In addition, the TOST procedure (Lakens 2017; Lakens et al. 2018) was used to test the hypothesis that mental fatigue has no worthwhile effect on half-marathon time (equivalence). The smallest effect size of interest (SESOI) was decided a priori, with lower (ΔL) and upper (ΔU) bounds set to -0.26 and 0.26 (i.e. -2.947 and 2.947 min on a raw scale). ΔL and ΔU corresponded to the latest meta-analysis effect size (Hedge's g) of cognitive exertion on aerobic performance (Brown et al. 2020).
2 ✕ 3 mixed-model ANOVAs (group x distance) were used to analyse differences in RPE, HR and running speed between the two groups during the half-marathon. When the assumption of sphericity was not met, the Greenhouse-Geisser correction was used. Significant interactions were followed up by testing simple main effects of the group at each distance with Bonferroni’s correction.
In the NHST analysis, statistical significance was accepted at P < 0.05 level. All data are presented as means ± SD, unless otherwise stated. RStudio (version 1.1.4; RStudio, Boston, MA) was used for the TOST equivalence testing analysis. The SPSS (version 23.0; SPSS, Chicago, IL) statistical package was used for all the other data analyses.