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Research

Our research has been presented at
Research is vital in understanding the effects of brain fatigue in athletes. Here, the first of a series of studies involving Soma NPT, shows how neurocognitive load changes the way athletes respond to their physical training.
Intro

In the past decade in the sport world, the attention and interest for neurocognitive processes relating to sport performance has drastically increased. Several studies have recently proved that neurocognitive interventions using computer-based or app-based tasks can produce significant changes in brain processes and affect fatigue perception. Therefore, there has been a lot of focus and attention on strategies to hack the brain to alter perception of effort and thus fatigue in order to boost performance outcomes.

Neurocognitive interventions that induce
brain fatigue can boost performance.

Some of those interventions, aimed to induced mental fatigue (defined as a psychobiological state caused by prolonged periods of demanding cognitive activity and characterized by subjective feelings of “tiredness” and “lack of energy”), have reportedly proved to decrease physical performance.

It has been argued that prolonged continuous cognitive activity (from 30 up to 90 min) of specific cognitive tasks, would produce a neurocognitive overload in the brain and thus alter one’s perception during any subsequent physical task.

Although overloading the brain has been proven deleterious for physical performance in its acute phase, there is, however, evidence that repetitions of acute stimuli in the form of organized training, may produce an adaptation that would result highly beneficial for performance.

Therefore, we present here the first of a series of investigations aiming to investigate the effect of neurocognitive overload (using SOMA NPT phone application) on physiological, psychological and perceptual responses during resistance training and endurance cycling performance.

Using two different studies, we tested the hypothesis that adding neurocognitive workload on top of traditional physical training would increase perception of effort during the resistance training session and would produce a negative effect on the endurance performance outcome.

Protocol schematic study

Using a randomized crossover design, 12 subjects visited the laboratory on 4 different occasions (two familiarizations and two experimental sessions)

Research methodology
study one

During the first familiarization session we determined individual 1 repetition maximum (RM) which is the maximum weight an individual can lift once in a specific exercise. We repeated it for the six exercises that they will later on perform in the resistance training session. 1 RM was used to determine the individual weight to use for each exercise during the experimental sessions.

After being properly familiarized with all tests and measurements, they completed a resistance training session (including 6 basic weight-training exercises) followed by a 20 min cycling time trial in two different conditions.

In one condition (SOMA NPT) they were completing app-based neurocognitive tests during pauses for each set or repetition of the resistance training and after that they completed another battery of cognitive tests for 30 min before beginning the cycling performance. In the control condition, the neurocognitive tests were replaced by emotionally neutral videos. Psychological questionnaires for mood (BRUMS), perceived workload (NASA TLX) and sessional RPE (Borg’s 0-10) were completed at beginning of each experimental visit and at completion of the resistance training session.

Cognitive function was assessed using 5 min of the psychomotor vigilant test (PVT) at beginning and at completion of each of the experimental condition. Power output, distance covered, hr, blood lactate and RPE (Borg’s 0-10) were recorded during the cycling time trial.

study two

12 subjects visited the laboratory on three different occasions in a randomized cross over order (one familiarization and two experimental sessions).

During familiarization session subjects performed unilateral leg extension of the dominant leg on an inclined bench with increasing weight to determine 1 RM similar to Study One. Meanwhile they were familiarized with the perception of effort scale RPE (Borg’s 0-10).

After 1 RM was established, we asked them to lift the equivalent of 20, 40, 60 and 80% of the 1RM previously recorded and hold it in extended position for 3 sec. After each lifting they reported their perception of effort pointing at the RPE scale.

Effort was defined as how hard they had to drive their leg to lift the weight without considering any burning sensation arisen from the muscles. During the experimental conditions, subjects filled the mood questionnaire (BRUMS) and they completed either a battery of neurocognitive tests for 90 min (SOMA NPT) or they watched an emotionally neutral video for the same amount of time (Control).

Afterwards, they completed again the mood questionnaire and they were asked to perform leg extensions (in the same way as in the familiarization) with four weights corresponding to 20, 40, 60, and 80% of the individual 1RM. Subjects lifted each weight three times with 2 min rest in a randomized order and completely blind of the weight applied. They rated their effort immediately after each lift using the RPE scale.

Soma increases rating of perceived exertion

Sessional Rating of Perceived Exertion (0-10)

Workload NASA TLX (0-100)

rpe

24%

mental demand

112%

physical demand

no diff

effort

103%

frustration

154%
Soma alters mood

Mood (BRUMS questionnaire) at the end of resistance training session showed significant higher value for anger, fatigue and boredom and a significant decrease in vigour in SOMA NPT condition compared to control.

Mood Brums (0-16)

Anger

86%

Fatigue

112%

Vigour

100%
Distance and mean power

Power output and distance covered were reduced by circa 7% in the SOMA NPT condition during the cycling time trial. However, no differences have been reported for HR and RPE, blood lactate instead was significantly higher in the control condition.

Finally, cognitive function measured as reaction time in PVT test was significantly impaired at the end of the experimental session in the SOMA NPT condition compared to the control one.

Distance, KM

Mean power, W

Distance

8%

mean power (20 km)

7.6%
Soma challenges cognitive function

Finally, cognitive function measured as reaction time in PVT test was significantly impaired at the end of the experimental session in SOMA NPT condition compared to the control one.

reaction time, ms

delta reaction time, ms

reaction time

82%
soma increases RPE

Results of the mood questionnaires showed that there is a significant difference in mood values (Anger, Confusion, Fatigue, Vigour and Boredom) due to SOMA NPT neurocognitive intervention compared to control. During the weight lifting task, there is a significant difference in RPE reported for each weight lifting. Values of effort are higher for each % weight in the SOMA NPT condition compared to control.

Rating of perceived exertion (0-10)

RPE

20%
Conclusion

In the present investigations (split in two studies) we proved that a combination of additional neurocognitive workload with tradition resistance training increased the perceived difficulty of a submaximal resistance training session leaving physiological parameters unaltered and without compromise the quality of the training session. The perceived difficulty showed in the SOMA NPT condition is likely due to the augmented mental workload reported by subjects which may have altered subject`s weight perception as also confirmed by results in Study Two (where RPE was higher when the brain has been previously overload with neurocognitive tasks). Moreover, outcomes during the cycling time trial showed that prolonged cognitive activity before a maximal endurance exercise had a negative impact on performance by altering one’s perception of effort and difficulty of the physical test.

Neurocognitive interventions make athletes mentally resilient to fatigue

The outcome of this investigation produces evidence that neurocognitive components are an important factor in sport performance and cannot be overlooked. In particular, it highlights that prolonged exposure to specific neurocognitive tasks can produce alteration in perception of effort and thus produce changes in performance outcomes. Similarly, it provided evidence that constructing training plans including neurocognitive interventions will benefit athletes by making them more mentally resilient to fatigue, without affecting their physical training load and routine.

Background and hypothesis

It has been hypostasized that the acute negative effect of mental fatigue could potentially become a training stimulus for the brain, in order to first adapt and then improve its ability to better sustain mental fatigue states, or even reduce such negative states, in particular during a stressful situation such as competition. It is very well known that intense physical training will produce a momentary reduction in performance and that the body will then adapt and super compensate, by creating the necessary changes to improve in that specific physical aspect. Therefore, it may be plausible to think that imposing a cognitive stimulus in the form of a series of cognitive tasks, on top of the normal physical training of athletes, may produce neural adaptation and consequently performance changes in physical tasks.

Up to date, there is only one unpublished study, which showed an improved endurance cycling performance in subjects undergoing mentally demanding training along with physical training (Marcora et al., 2015). They used a specific cognitive training called brain endurance training (BET) which is a new training method that uses acute mental fatigue as a training stimulus to induce chronic reductions in fatigue during physical and/or cognitive tasks.

Cognitive overload with brain endurance training boosts performance in professional football players

Therefore, we present here a training study aimed to test the efficacy of BET using SOMA NPT, a phone-based app inducing neurocognitive fatigue in a battery of cognitive and physical sport specific tests in players from a professional football team. We hypothesised that the combination of BET and standard physical training during a 4-week training period, increases cognitive capacity and physical football performance, by reducing the rating of perceived exertion (RPE) and increasing resilience to fatigue more than standard physical training alone.

Research methodology

Using a randomized controlled trial design, we assessed the efficacy of BET + traditional football training (SOMA NPT Training) against traditional football training only (Control) in a professional football team during pre-season period. We randomly allocated 22 male football players (randomization was effectuated considering also player role so to have a counterbalanced random order) to either SOMA NPT training or Control. Participants were tested at baseline (pre-test) and after 4 weeks of training (post-test). Analysis (Mixed ANOVAs) compared differences between the 2 groups in two different time points: Pre and Post training.

training procedures

• Participants allocated to the control group performed the normal training routine without performing any cognitive task (traditional physical training). However, to avoid any biased results as control group was not performing any specific cognitive training, they were asked to listen to a specific sound at the end of each training session (for the same amount of time as SOMA training group). They have been told that the sound was another type of training inducing relaxation, although it was just a neutral sound which did not produce any positive or negative effects on the players.

• Participants allocated to the SOMA training group undertook the normal training routine as all other members of the team. On top of the physical training, at the end of each training session they completed a specific cognitive task (players could choose between 5 different tasks to complete) for a time between 20 and 30 min (from 3 to 5 times a week).

For both groups, during the 4-week training, between 20 and 25 training sessions have been completed. The SOMA training group completed on average 400 min of cognitive training during the 4-week period. NASA-TLX Scale was used to measure the subjective workload (Mental and Physical Demand) of each of the training sessions.

testing procedures

• VISIT 1: “FAMILIARIZATION”. All participants were familiarized with the testing procedures and protocols of the battery of cognitive (STROOP and PVT tasks) and physical (30-15 IFT, Repeated Sprint Ability -RSA- and Specific Reactive Agility) tests and with psychological questionnaires.

• VISIT 2: “30-15 INTERMITTENT FITNESS TEST (IFT)”. All participants completed this specific YO-YO test developed by Buchheit (2008). This type of test is well known, validated and a standard procedure for players. It can be used to assess the physical fitness of footballers. Distance covered was measured as performance outcome. Physiological measures of HR and Blood Lactate were taken at the end of the test.

• VISIT 2: “STROOP TASK”. At completion of the 30-15 IFT all participants completed 30 min of a high demanding cognitive task for response inhibition and sustained attention, the STROOP colour test. Previous studies (Martin et al. 2016) have proved that this test is a good indicator of ability to inhibit from negative responses and to sustain prolonged periods of attention. Reaction time and Accuracy over the 30 min task were measured at the end of this task.

testing procedures

• VISIT 3: “SPECIFIC REACTIVE AGILITY TEST”. All participants performed this specific custom made agility test in which athletes were asked to complete a circuit of 5 + 1(base) lights attached on a pole (each light on one pole) in semi-circlea round the base light, each pole was 4 m away from the base point (see Fig. 1).

Participants’ goal was to react to the light signal and run toward it to touch it and then come back to a base point. Moreover, participants were asked to touch the lights on their left side (2 lights) with the right hand and the lights on the right side (2 lights) with the left hand. Free choice was given for the 1 central light. Athletes needed to complete three sets of 10 lights each with 20 sec recovery in between. Light signals appeared in a counterbalanced random order. Each light from each pole appeared twice. Time to complete the three sets of lights was recorded as long as errors produced by touching the light with the wrong hand (Accuracy). Physiological measures of HR and Blood Lactate were taken at the end of this test.

Figure 1: Specific Reactive Agility Test

• VISIT 4: “RSA RANDOM TEST”. The test (Fig.2 taken from reference below) consisted of 6 × 20-m (10-m+ 10-m) sprints separated by 20 seconds of active recovery while jogging back to the initial position (Martin et al. 2018). Each sprint was compounded by a 10-m linear sprint plus a 10-m sprint with three potential directional options according to a traffic light fixed after the first 10-m linear sprint (Martin et al. 2018).
Average time of 10-m linear sprint (acceleration) and time of 10-m directional sprint (decision making) were taken. Physiological measures of HR and Blood Lactate were taken at the end of this test.

• VISIT 5: “PSYCHOMOTOR VIGILANCE TEST (PVT)”. Before the RSA Random Test and at completion of it, all participants completed 10 min of the PVT Test, a cognitive test extensively used to assess reaction time and fatigue. Measures of reaction time for overall 10 min test were taken along with number of lapses (responses slower than 500 ms).

The battery of tests at baseline and at post training interventions were performed in the same conditions. Athletes were asked to abstain from physical exercise for 24 h before the test so that all tests were performed under the same standardized circumstances (temperature, time of the day…) and with players properly rested. There was a minimum period of 48 hours in between each visit. Questionnaires for mood and motivation were given at beginning of each testing session to assess mood state and level of motivation of players in engaging the battery of tests.

Figure 2: RSA Random Test

• VISIT 4: “RSA RANDOM TEST”. The test (Fig.2 taken from reference below) consisted of 6 × 20-m (10-m+ 10-m) sprints separated by 20 seconds of active recovery while jogging back to the initial position (Martin et al. 2018). Each sprint was compounded by a 10-m linear sprint plus a 10-m sprint with three potential directional options according to a traffic light fixed after the first 10-m linear sprint (Martin et al. 2018).
Average time of 10-m linear sprint (acceleration) and time of 10-m directional sprint (decision making) were taken. Physiological measures of HR and Blood Lactate were taken at the end of this test.

• VISIT 5: “PSYCHOMOTOR VIGILANCE TEST (PVT)”. Before the RSA Random Test and at completion of it, all participants completed 10 min of the PVT Test, a cognitive test extensively used to assess reaction time and fatigue. Measures of reaction time for overall 10 min test were taken along with number of lapses (responses slower than 500 ms).

The battery of tests at baseline and at post training interventions were performed in the same conditions. Athletes were asked to abstain from physical exercise for 24 h before the test so that all tests were performed under the same standardized circumstances (temperature, time of the day…) and with players properly rested. There was a minimum period of 48 hours in between each visit. Questionnaires for mood and motivation were given at beginning of each testing session to assess mood state and level of motivation of players in engaging the battery of tests.

Cognitive test results: stroop test

Results in the Stroop task showed that reaction time in both groups decreased from pre to post training (Fig. 3). However, SOMA NPT training group decreased significantly (p < 0.02) more compared to the control condition, despite no significant differences in the accuracy (Fig. 4).

Figure 3: Reaction Time (ms)

Figure 4: Accuracy (%)

reaction time
(soma)

11%

reaction time
(control)

3.7%
Cognitive test results: PSYCHOMOTOR VIGILANCE TEST (PVT)

The PVT task performed before and after the RSA Random test in pre-and in post training did not show any significant differences for reaction time (Fig. 5) in both groups. However, at post-test a significant difference
(p < 0.02) was found for lapses. SOMA training group performed with less lapses (slow responses) at post compared to the control condition (Fig. 6).

Figure 5: Reaction time (ms)

Figure 6: Number of lapses

number of lapses
(soma)

40%

number of lapses
(control)

no diff
Physical test results: 30-15 INTERMITTENT FITNESS TEST (IFT)

Distance covered during the 30-15 test showed that there was no difference in the performance of SOMA NPT training group from pre- to post-training (Fig. 7). However, the control group showed a significant decrease (p < 0.05) in performance at post-training (Fig. 7). The lack of general improvement in this test may be due to logistic reasons as this test was the only one performed very soon after the end of the 4-week training. So, potentially, some residual fatigue or functional overreaching was still present. No significant changes were found for physiological variables of HR and Lactate between the two groups.

Figure 7: 30-15 IFT Distance (m)

30-15 IFT
(soma)

no diff

30-15 IFT
(control)

8%
Physical test results: SPECIFIC REACTIVE AGILITY TEST

The PVT task performed before and after the RSA Random test in pre-and in post training did not show any significant differences for reaction time (Fig. 5) in both groups. However, at post-test a significant difference (p < 0.02) was found for lapses. SOMA training group performed with less lapses (slow responses) at post compared to the control condition (Fig. 6).

Figure 8: Time, S

Figure 9: Number of errors

time (soma)

8.3%

Time (control)

4.7%

Errors (soma)

74%

Errors (control)

10%
Physical test results: RSA RANDOM TEST

During the RSA Random Test no significant differences were found between the two groups from pre to post training for linear acceleration phase (first 10 m) (Fig. 10). However, a significant difference (p < 0.05) was found for the decisional phase (second 10 m). Players in the SOMA training group completed the decisional phase of sprint, on average, faster than the control group (Fig. 11). No significant changes were found for physiological variables of HR and Lactate between the two groups.

Figure 10: Acceleration time, s

Figure 11: Decision making time, s

Decision time
(soma)

8%

decision time
(control)

4%
Training phase

During the 4 week training players in the SOMA NPT training group showed, through the NASA TLX questionnaires, constantly significantly higher (p < 0.01) cognitive/mental demand rates for the training sessions compared to control (Fig. 11). While, no significant differences were found for the physical demand rates which was the same.

NOTE: No significant differences were found for MOOD and MOTIVATION at the beginning of each testing session as proof that mood states and motivation showed always similar results before commencing the battery of tests.

No significant changed between groups at post training for HR and Blood lactate indicates that all players undertook similar physical training load during the pre-season training period.

Figure 12: Cognitive workload

TRAINING WORKLOAD
(SOMA VS CONTROL)

22%
Conclusion

The results of this study provide initial evidence that the combination of BET through the SOMA NPT app and standard football training is more effective than standard training alone in boosting cognitive and physical performance in elite football players. As shown in previous studies on mental fatigue and sport performance, this type of cognitive training targets specific areas of the brain by altering the perception of effort for a given task. Therefore, the cognitive overload produced in BET can induce over a period of training (4 weeks for the present study) a reduction in the perception of effort for a specific task, compared to a control condition, and thus improvement in performance. The improved performance can be seen as a boost in the resilience of players in dealing with fatigue. As cognitive and physical fatigue share similar patterns in the brain, the improvement of the BET group (with SOMA NPT) has been seen in both football specific physical tests as well as for generic cognitive tasks such as STROOP and PVT.

The outcome of this investigation produces evidence that neurocognitive components are an important factor in sport performance and cannot be overlooked. In particular, it highlights that prolonged exposure to specific neurocognitive tasks can produce alteration in perception of effort and thus produce changes in performance outcomes. Similarly, it provided evidence that constructing training plans including neurocognitive interventions will benefit athletes by making them more mentally resilient to fatigue, without affecting their physical training load and routine.

references

Marcora SM, Staiano W, Merlini M, editors. A randomised controlled trial of Brain Endurance Training (BET) to reduce fatigue during endurance exercise. 62nd Annual Meeting of the American College of Sports Medicine; 2015 May 26–30; San Diego (USA): American College of Sports Medicine.

Buchheit, M. (2008). The 30-15 intermittent fitness test: accuracy for individualizing interval training of young intermittent sport players. J. Strength Cond. Res. 22, 365–374. doi: 10.1519/JSC.0b013e3181635b2e.

Martin K., Staiano W., Menaspà P., Hennessey T., Marcora S., Keegan R., et al. (2016). Superior inhibitory control and resistance to mental fatigue in professional road cyclists. PLoS One 11:e0159907.

Martin, V., Sanchez-Sanchez, J., Ramírez-Campillo, R., Nakamura, F., & Gonzalo-Skok, O. (2018). Validity of the RSA-RANDOM Test for Young Soccer Players. International Journal of Sports Medicine. doi:10.1055/a-0637-2094.

Background

We present here, the second study of this series of investigations aiming to assess the effect of neuro-cognitive overload inducing mental fatigue (using SOMA NPT phone application) on physiological, psychological and perceptual responses during repeated sprint and jump ability and YO-YO test in a group of well-trained subjects. Those tests are prominent and of paramount importance in a Team Sport environment such as Handball, Football and Basketball.

Research methodology

12 subjects visited the laboratory on three different occasions (one familiarisation and two experimental sessions) in a randomised cross over order of experimental sessions. During visit 1 all participants were familiarised with the testing procedures and the battery of cognitive (Stroop and PVT tasks) and physical (YO-YO, Repeated Sprint and Jump Ability) tests and with psychological questionnaires (RPE, BRUMS, and NASA TLX). Afterwards, with a minimum of 7 days in between sessions, participants reported to the laboratory facility to complete the 2 experimental sessions described in the following protocol.

Protocol

Participants were asked to report to the lab where they completed the BRUMS questionnaire for mood assessment. After that, they were asked to complete 10 min of the Psychomotor Vigilant Test (PVT) to assess reaction time and readiness.

At completion of the PVT task, depending on the experimental condition, they completed either 30 min of a highly demanding cognitive task aimed to induce mental fatigue (Stroop Task) (SOMA NPT condition) or they watched a neutral documentary for the same amount of time (Control condition).

At completion of the experimental condition, they performed again 10 min PVT and completed the BRUMS questionnaire and the NASA TLX to assess cognitive workload during the experimental conditions. Afterwards, they moved to the court and they performed a battery of three physical tests in the order listed below and with 15 min rest between each test.

Figure 1: Specific Reactive Agility Test

1. RSA RANDOM TEST. The test consisted of 6 × 20-m (10 + 10-m) sprints seperated by 20 seconds of active recovery while jogging back to the initial position repeated twice (Fig. 1). Each sprint was compounded by a 10-m linear sprint plus a 10-m sprint with three potential directional options according to a traffic light fixed after the first 10-m linear sprint (Martin et al. 2018). Average time of 10-m linear sprint (acceleration) and time of 10-m directional sprint (decision making) were taken. Physiological measures of HR and Blood Lactate were taken at the end of it.

2. REPEATED JUMP AND REACH TEST. All participants completed a series of vertical jump tests, which consisted of a jump-and-reach trial from a standing position every 5 sec for 3 min (30 jumps in total). Average power W/kg was measured (force plate) through all jumps and also average height reached (Stick for jump and reach test). This test is an adaptation of Bosco repetitive jump test (1983).

3. 30-15 INTERMITTENT FITNESS TEST (IFT). All participants completed this specific type of YO-YO test developed by Buchheit (2008). This type of test is well known, validated and a standard procedure for players. It can be used to assess the physical fitness of footballers. Distance covered was measured as performance outcome. Physiological measures of HR and Blood Lactate were taken at the end of the test.

Participants were asked to abstain from physical exercise for 24 h before the test so that all tests were performed under the same standardised circumstances (temperature, time of the day…) and with subjects properly rested. A minimum period of 7 days was in between each visit.

PSYCHOLOGICAL QUESTIONNAIRES

As already shown in Study 1 of this series, 30 min of a demanding neuro-cognitive task (SOMA NPT) produced an alteration in the mood of participants who exerted significantly higher levels of anger, confusion and fatigue scales compared to the control condition and a lower vigour (p < 0.05)(Fig. 2). Those are all signs of mental fatigue. Moreover, participants rated the neuro-cognitive tasks as more mentally demanding, effortful and frustrating compared to the control condition (Fig. 3).

Figure 2: Mood Brums (0-16)

Anger

94%

Confusion

25%

Fatigue

96%

Vigour

99%

Figure 3: Workload NASA TLX (0-100)

mental demand

110%

Physical demand

no diff

effort

99%

frustration

119%
Cognitive test results: PSYCHOMOTOR VIGILANCE TEST (PVT)

The PVT task performed before and after the experimental conditions showed a significant difference at post intervention for reaction time (Fig. 4). SOMA NPT condition seems to slow down PVT in participants more than the control condition.

Figure 4: PVT, Reaction Time (ms)

reaction time

50%
physical test results: RSA RANDOM TEST

During the RSA Random Test no significant differences were found between the two conditions for the linear acceleration phase (first 10 m) (Fig. 5). However, a significant difference (p < 0.05) was found for the decisional phase (second 10 m). Participants in the SOMA NPT condition completed the second phase of the sprint, on average, slower than the control condition (Fig. 5).

Figure 5: RSA Results, time (s)

Acceleration
phase

no diff

Decision
making

50%
physical test results: REPEATED JUMP-AND-REACH TEST

At completion of the Jump-and- reach test, participants in both conditions on average produced less power when comparing the first minute to the last one. However, when mentally fatigued, participants showed a significantly higher (p < 0.05) decrease in power compared to the control condition (Fig. 6). A similar pattern was found for average jump height which was lower in the SOMA NPT condition compared to the control.

Figure 6: Jump and Reach Power (W) and Height (cm)

Avg jump power

6.5%

AVG Jump height

8.6%
physical test results: 30-15 INTERMITTENT FITNESS TEST (IFT)

During this specific YO YO test results showed that mentally fatigued participants (SOMA NPT) showed a significant decrease (p < 0.05) in distance covered compared to the control condition. (Fig. 7).

For all three physical tests, no significant differences between conditions was found for physiological parameters of HR and Blood Lactate measured during and at completion of the tests.

Figure 7: 30-15 IFT Distance (m)

30-15 ift distance

10.8%
Conclusion

In this second study (in line with previous results from the first study) we proved that 30 min of demanding neuro-cognitive tasks, aimed to overload the brain, affects physical performance in team sport specific physical tests.

As stated in the first study, a probable cause of the decrease in performance is due to alteration of the perception of effort because of the cognitive overloading task (SOMA NPT).

The outcome of this investigation confirms previous results from the first study we completed and reiterate the importance of neuro-cognitive factors in sport performance (in particular team sport as reported in this study).

Introduction

In the previous studies in this series we have discussed the impact of cognitive load using prolonged and continuous demanding tasks on sport performance. We have understood the role of mental fatigue and how this phenomenon has a negative effect on performance as well as mood and perception of effort. However, what occurs in the brain when fatigue starts increasing in response to cognitive load has been the object of research in past decade [Boksem et al. 2005, Van Cutsem et al. 2017]. In the present study we aimed to understand how cognitive load may generate fatigue while engaging in a cognitive task (STROOP) and we will measure not only its effects on cognitive performance (using Psychomotor Vigilant Task, [PVT]) and perception of effort (RPE) but we will also assess changes in brain activity using a well-known neurophysiological tool: Electroencephalography (EEG).

Research methodology

12 subjects visited the laboratory on two occasions (one familiarization and one experimental session). During familiarization, subjects were familiarized with two cognitive tasks: STROOP Colour test and PVT. Meanwhile they were familiarized with the perception of effort scale RPE (Borg’s 0-10). During the experimental session, they reported to the lab and they were asked to complete 4 five-min PVT. In between each PVT, subjects completed 30 min of STROOP. In total subjects completed 90 min of STROOP divided into three tasks and 20 min of PVT divided into 4 tasks. The overall protocol consisted in:

PVT+ STROOP+ PVT+ STROOP+ PVT+ STROOP+ PVT

We used the STROOP task to mentally fatigue our subjects due to its sustained attention and response inhibition component and we were assessing their cognitive performance using the PVT a golden standard for assessing vigilance and attention. At the end of each PVT and STROOP, subjects were asked to rate the RPE of the current task they were performing (but taking into consideration the accumulated fatigue of previous ones). Throughout all sessions we were recording brain activity using a portable wireless EEG device. We used Power Spectrum Analysis to define different bands of brain activity (Alpha, Beta and Theta). In the literature there is evidence that suggest a series of neurophysiological indices of cognitive load and brain fatigue that can be detected.

During mental workload and sustained attention, it has been found that theta power increases because more attentional resources are demanded [Clayton et al. 2015]. Beta power instead decreases with increasing of fatigue [Jap et al. 2009]. Moreover, recent studies (Wascher et al. 2014; Boksem et al. 2005) reported that mental fatigue is related with an increase in frontal alpha activity. Finally, there are studies that used different ratios of those bands to produce reliable biomarkers of fatigue. The ratio of (Alpha + Theta)/Beta, one of the most used, increases with fatigue [Jap et al. 2009]. For the purpose of this study we will use averaged brain indices from the frontal area of the brain which is one of the main areas involved in fatigue, attention and cognitive load.

Effect of cognitive load on vigilant attention (PVT)

The progressive increase of cognitive load and subsequent fatigue through the 3 STROOP tasks produced a significant and progressive increase in reaction time (Fig. 1), lapses (amount of responses above 500ms) (Fig. 2) and variation (Fig. 3) in the PVT. The increase of such variables and thus decrease in cognitive performance seemed to follow a linear trend through the 90 min of the mentally demanding tasks. RPE provided a good subjective indicator of cognitive effort as it increased significantly through all the PVT tasks (Fig. 4).

Figure 1: Reaction time, MS (PVT)

Figure 2: Lapses (PVT)

Figure 3: Variation, % (PVT)

figure 4: RPE (PVT)

reaction time:

44%

Lapses:

105%

Variation:

74%

RPE:

45%
Mental fatigue and STROOP

Similarly to PVT, subjects showed a detrimental effect of cognitive performance performing the 3 STROOP tasks. From 30 to 90 min there is a significant increment of reaction time (Fig. 5) and Variation (Fig. 6) and a decrease in Accuracy (Fig. 7). Again, RPE was also significantly elevated at completion of the last STROOP (Fig. 8).

figure 5: Reaction time, ms (Stroop)

figure 6: Variation, % (Stroop)

Figure 7: Accuracy, % (stroop)

Figure 8: RPE (stroop)

reaction time:

15%

Accuracy:

1%

Variation:

55%

RPE:

45%
Brain indices of fatigue using EEG

Theta band significantly increased when comparing minutes of tasks from the first ones throughout the last ones (Fig 9). Similar trend can be found for alpha band (Fig. 9) which increases as well in relation with the increase of fatigue due to the cognitive demand. However, beta band power showed a slightly decrease in power (Fig. 9). The ratio (Alpha+Theta)/Beta was in line with previous studies and showed a significant increase at the end of the 90 min of cognitive load (Fig. 10).

Power band

figure 9: Power, (μV2)

figure 10: Power, (μV2)

Alpha:

30%

beta:

38%

theta:

63%

Ratio:

157%
Conclusion

The present study shows how an increase in cognitive load after 90 min of demanding and continuous cognitive tasks can produce a negative effect in vigilance, reaction time and perceived effort. More importantly, EEG measures helped to unveil the neurophysiology behind such changes in performance due to fatigue, and it can help to quantify quantified cognitive load in an objective manner. Moreover, neurophysiological assessments of load and fatigue will help us understand better how the brain works and copes with an increasing load. Moreover, it may help us to measure possible brain changes in responses to different types of cognitive trainings (i.e BET).

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