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Effects of Judo on Neurocognitive Indices of Response Inhibition in Preadolescent Children: A Randomized Controlled Trial

LUDYGA, SEBASTIAN; TRÄNKNER, SEBASTIAN; GERBER, MARKUS; PÜHSE, UWE

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Medicine & Science in Sports & Exercise: August 2021 - Volume 53 - Issue 8 - p 1648-1655
doi: 10.1249/MSS.0000000000002626
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Abstract

From a developmental perspective, activities and programs that seek to promote children and adolescents’ executive function (i.e., top-down control of behavior) are of high importance because this cognitive domain is closely related to their academic (1) and mental health outcomes (2,3). Within the category of interventions that involve the modification of behavior, regular exercise engagement has been suggested to effectively enhance executive function (4). However, the current evidence does not support a general effect of exercise but rather highlights the need to consider its characteristics to maximize potential benefits (5). In this respect, recommendations derived from meta-regressions encourage the participation in exercise programs with high coordinative demands across all age groups to effectively improve executive function and other cognitive domains (6). This might be due to the effects of exercise types with high coordinative demands on complex motor skills (7), which in turn are closely related to executive function (8,9). In addition, experimental studies further suggest that regular participation in exercise with increased cognitive load leads to cognitive benefits in children (10,11). Both cognitive and coordinative challenges are inherent parts of martial arts, so that sports falling in this category are highly promising candidates for the promotion of executive function. The limited experimental evidence further supports benefits for this cognitive domain after regular engagement in martial arts (12,13).

Comparing the different components of executive function, there is a tendency for a higher sensitivity of inhibitory control to regular exercise engagement (14,15). Interference control (i.e., the resistance to distractions at a perceptual level and the suppression of prepotent mental representations) and response inhibition (i.e., suppression of a prepotent behavioral response) are subtypes of this cognitive ability (16). Evidence showing improved inhibitory control after regular exercise engagement was mainly generated by studies that investigated interference control. This one-sided focus needs to be addressed, given that response inhibition allows for conclusions on the engagement in unhealthy and unwanted behaviors that cannot be drawn from individuals’ interference control. For example, poor response inhibition is a predictor of substance abuse (17), excessive drinking (18), and Internet Gaming Addiction (19).

Response inhibition can be assessed with a Go/NoGo task, which requires a motor response from participants in Go trials but the suppression of such response in NoGo trials. When this task is combined with electroencephalographic recordings, event-related potentials (ERPs) elicited by the two trial types provide an opportunity to study specific cognitive processes along with behavioral performance. Conflict monitoring is indexed by the N2, which is a negative deflection with a frontal distribution in the 250- to 350-ms latency range (20). This component usually shows a larger negativity in response to NoGo relative to Go trials because of the imposed response conflict. The N2 is followed by a large amplitude with a positive peak in the 300- to 600-ms latency range. Depending on the topography of this component, it can be subdivided into the P3a (elicited from NoGo trials) and P3b (elicited from Go trials) for a frontocentral and parietal distribution (21,22), respectively. Their functional significance differs, so that the P3a is related to frontal lobe activity required for stimulus evaluation, whereas the P3b indexes temporoparietal activity associated with the allocation of attentional resources toward the task (23).

Based on a review of the current literature, high aerobic fitness and regular engagement in physical activity have been linked with a modulation of P3b across different age groups and executive function tasks, with the majority of studies reporting an increased amplitude of this component (24). The few randomized controlled trials that investigated long-term effects of exercise in children and adolescents further support an increase of the P3b amplitude (elicited from interference control tasks) after aerobic exercise (25) or its combination with coordinative exercise (26). In these age groups, the lack of experimental evidence on exercise-induced alteration of cognitive processes indexed by the N2 and P3a is even more pronounced. However, cross-sectional studies found differences in the N2-P3 complex, which was elicited from an interference or response inhibition task, between high-fit and low-fit children and adolescents (27,28). These results assume an association between cardiorespiratory fitness and inhibition-related ERPs, but they allow no insights into the type of exercise that is most likely to benefit processes indexed by the N2 and P3a/b components.

Because of the potential of martial arts to enhance performance on executive function tasks (12,13), the neurocognitive profile of athletes that mastered these sports may provide further indications on the mechanisms underlying this effect. In this respect, higher judo expertise has been related to both greater N2 and P3b peak in an interference control task (29). Moreover, skilled martial arts athletes compared with novices showed more pronounced P3a source activity differences between different trial types of a continuous performance task (30), suggesting a greater reserve for increasing focal attention for the evaluation more demanding stimuli (23). Similar results on the N2-P3 complex were obtained from athletes experienced in combat sports, which share commonalities with martial arts. In comparison to nonathletes, professional fencers and boxers both had higher negative N2 and positive P3a amplitudes on NoGo trials (31). These insights either indicate a promotion of effective conflict monitoring and attention processes or an attraction of individuals with a specific neurocognitive profile by martial arts and related sports. The examination of martial arts–induced changes in cognitive control processes may allow for novel insights into neurocognitive mechanisms underlying executive function and response inhibition in particular. Especially judo may be a promising candidate as it shares cognitive and coordinative demands with other martial arts, but showed the lowest injury rates in this sports category among pediatric populations (32).

The present randomized controlled trial investigated the effects of a 3-month judo training program on neurophysiological indices of response inhibition (N2, P3a, and P3b) and behavioral performance on the Go/NoGo task in preadolescent children. Because meta-analytical findings consistently found improvements of inhibitory control after regular exercise engagement (14,15), the judo training was expected to reduce error rates on NoGo trials. Based on the neurocognitive profile of martial arts athletes (29–31), greater increases in N2 negativity and/or P3a/b amplitudes over the intervention period were assumed in the judo training group compared with the control group.

METHODS

Participants

The study protocol was registered at the DRKS (DRKS00017403) and approved by the local ethics committee (Ethikkommission Nordwest- und Zentralschweiz). Participants were recruited via flyers and an advertisement in a local newspaper in Basel, Switzerland. The required sample size was determined a priori using G*Power 3.1.9.4. Meta-analytical findings reported small-to-moderate effects of exercise on executive function in children and adolescents. The few experimental studies that investigated the influence of martial arts on this domain consistently reported large effects on behavioral performance and parent ratings (12,13). Considering a moderate effect (based on the average of previous meta-analyses and experimental studies), P = 0.05, and a dropout rate of 10%, 42 participants were required to reach 85% power on a repeated-measures ANOVA. Inclusion criteria were age 9 to 13 yr, right-hand dominance, corrected to or normal vision, and no regular engagement (defined as one or more per week) in any type of martial arts within 3 months before the first laboratory visit. Participants attending special education services related to cognitive impairments or attentional disorders, those undergoing pharmacotherapy for any mental disorder, and those with color blindness and/or any medical condition that causes an elevated health risk during exercise activities were excluded. Recruited participants expressed their willingness to take part in the study, and their legal guardians provided informed written consent. All study procedures followed the guidelines set forth in the Declaration of Helsinki and its amendments.

Study design

Participants were randomly allocated to a martial arts group (MAG) and a wait-list control group (CON) in a 1:1 ratio and with age used as stratum. A possible selection bias was prevented by using concealed allocation. Participants completed one baseline and one follow-up laboratory visit after 3 months at the same time of the day. The sequence of assessments was identical in both visits, with the exception that two questionnaires were administered at baseline only. First, participants completed cognitive testing, which included a computerized Go/NoGo task with simultaneous recording of ERPs via EEG. Second, they were asked to fill in the Strengths and Difficulties Questionnaire, the Family Affluence Scale, and the 7-d physical activity recall protocol to assess psychopathology, socioeconomic status, and physical activity, respectively. In addition, the screening items of the Intelligence and Development Scales-2 were administered. Third, after the measurement of body weight using a weighting scale (Tanita BC-601, Tokyo, Japan) and the collection of other anthropometrics, participants completed the Movement Assessment Battery for Children—version 2 (MABC-2) and a submaximal cycling ergometer test. To control for the engagement in new sports activities that are unrelated to the intervention, at follow-up, legal guardians were asked if participants started additional sports activities with at least one weekly session. The number of new activities and the weekly dose was collected. With regard to standardized preparation for measurements, participants were asked to refrain from any sports activities on the day of the laboratory visit and to have their last meal 2 h before testing. Assessments were completed, with surrounding noise reduced to a minimum and the environmental temperature held constant at 21°C to 22°C.

Intervention

The exercise intervention of the MAG comprised two 60-min judo sessions per week over a period of 3 months. Participants completed the exercise sessions in a group setting in a local dojo and were supervised by trained judo instructors. The training was tailored to children with no prior experience in martial arts and aimed at learning basic judo techniques for attack and defense as well as falling techniques for injury prevention. Each Judo session included blocks of children-appropriate and playful physical fitness training, technique learning, and their application in Randori (free fighting on the ground or while standing). To assess the intensity of the judo intervention, participants were asked to rate perceived exertion on a children-appropriate RPE scale immediately after four judo sessions within the second month of the intervention period. Participants allocated to CON had the opportunity to complete the judo training after the follow-up assessment.

Motor skills and cardiorespiratory fitness

The MABC-2 is characterized by a high reliability, factorial validity, and sensitivity to developmental changes (33,34). Depending on the participant’s age, the appropriate version of the MABC-2 (≤11 or ≥12 yr) was administered. This instrument assesses fine and gross motor skills from items categorized into manual dexterity (three items), balance skills (three items), and aiming/catching (two items). Age and sex-corrected standard scores were derived from raw scores of each subscale. These were combined to yield a standard score for the overall motor skills.

The physical work capacity at 170 bpm test (PWC170) has adequate test–retest reliability in children and adolescents (35), and relative power output assessed from 2-min stages compared with 3- and 6-min stages showed the highest correlation with the maximal oxygen uptake (36). Participants received a heart rate monitor with a chest belt (V800; Polar Electro Oy, Kempele, Finland) and were seated on a child-appropriate cycling ergometer (E200 P; COSMED, Rome, Italy). They were instructed to maintain a constant pedaling cadence between 70 and 80 rpm throughout the test. After an initial workload of 20 (body weight <50 kg)/30 W (body weight ≥50 kg), the workload was increased every 2 min based on the heart rate within the last 10 s within the actual stage. Stopping criteria were a heart rate exceeding 165 bpm, the inability to maintain the target pedaling cadence any longer, and/or the unwillingness of the participant to continue. These criteria were evaluated by the experimenter, and if one or more conditions were met, the test was terminated. Taking into account the seconds completed in the final stage, relative power output was calculated by dividing the final workload by the participant’s body weight.

Cognitive task

Participants completed a computerized Go/NoGo task, which was administered with E-Prime 2.0 (PST, Pittsburgh, PA). Neurophysiological indices elicited by this task have been characterized by long-term stability and high test–retest reliability (37). The task consisted of 30 practice trials, followed by three blocks with 100 trials each. A previous study found a visual Go/NoGo task with a similar number of trials to be a valid measure of response inhibition in children (38). Participants were instructed to press a button on a serial response box (Celeritas; PST) on Go (30%) and GoFrequent trials (40%), but to withhold their response on NoGo trials (30%). The probabilities of standard Go and NoGo trials were equal to reduce potential bias arising from frequency-related effects. Gray geometric shapes served as visual stimuli and were presented against black background. The color of their contour lines (pink, yellow, or blue) indicated the trial type. Colors were matched by intensity, and their assignment to trial types remained the same throughout the task. Visual stimuli were presented for 150 ms, and responses were collected within 850 ms after their onset. To reduce a potential influence of guessing, the interstimulus interval varied randomly between 1200 and 1400 ms. Reaction time on response-correct Go trials as well as commission (i.e., pressing a button in response to NoGo trials) and omission error rates (i.e., pressing no button in response to Go trials) were calculated and extracted for statistical analyses.

EEG recording and processing

For electroencephalographic recordings, 64 active electrodes were arranged in accordance with the 10:10 system and mounted on the participant’s head using a flexible head cap. Cz served as online reference, and AFz as ground. All electrodes were filled with highly conductive gel to reduce the scalp impedance to 10 KΩ or lower (for at least 90% of all electrodes). Data were amplified, band-pass filtered (0.01–100 Hz), and digitized with a sampling rate of 500 Hz (ActiCHamp; BrainProducts, Gilching, Germany). BESA Research 7.0 (Brain Electric Source Analysis, Gräfelfing, Germany) was used for offline processing of collected data. Based on virtual HEOG and VEOG channels, blinks were detected and corrected using automatic adaptive artifact correction. This method utilizes principal component analysis on continuous EEG data to separate artifact components from brain signals. Artifacts that survived the correction procedure were rejected based on individual gradient (M = 75 μV, SD = 0.6 μV) and amplitude thresholds (M = 118 μV, SD = 19.4 μV), which were applied after high-pass filtering (forward phase shift of 0.1 Hz; slope 6 dB per octave) and baseline correction (−200 ms to stimulus onset). For both response-correct Go (baseline: M = 66.6, SD = 10.4; follow-up: M = 64.1, SD = 11.9) and NoGo trials (baseline: M = 49.2, SD = 10.7; follow-up: M = 50.7, SD = 12.9), averaged segments over a latency range from −200 to 800 ms relative to stimulus onset were created. The resulting segments were low-pass filtered (zero-phase shift of 30 Hz; slope 24 dB per octave), and the reference was changed to average mastoids. The selection of time windows for the extraction of ERP components was guided by previous research (20–23) and verified by visual inspection of the data (i.e., the selected latency range covered the rising amplitude, the peak, and the falling amplitude of the grand-averaged ERP components). The Go and NoGo N200 were derived as the mean amplitude at the frontal region (average of AFz, AF3, AF4, Fz, F1, F2) in the time period from 250 to 380 ms after stimulus onset. The mean amplitudes in the latency range from 400 to 650 ms after stimulus onset were calculated at frontocentral and centroparietal regions to derive the NoGo-related P3a and Go-related P3b, respectively.

Statistical analyses

Descriptive and inferential statistical analyses were conducted with SPSS 25.0 (IBM, Armonk, NY). In advance, the normal distribution of collected data was checked using the Shapiro–Wilk test and homogeneity of variances was tested with Levene’s test. One-way ANOVA was applied to assess possible baseline differences in anthropometrics, socioeconomic status, psychopathology, and intelligence between MAG and CON. Variables showing a statistically significant and/or at least a moderate effect were considered confounders in subsequent main analyses. The intervention effect on behavioral indices of the Go/NoGo task (commission and omission error rates) was estimated by using separate two (group: MAG, CON) by two (time: baseline, follow-up) ANCOVA, which accounted for a speed–accuracy trade-off by including changes in Go reaction time as a covariate. Similar repeated-measures AN(C)OVA was applied to assess the effects of the intervention on ERP components (N200, P3a, P3b), fine and gross motor skills (MABC-2 score), and physical working capacity (PWC170), while controlling for covariates, if necessary. The main effect of time and possible time–group interactions were reported. In case of statistically significant time–group interactions for ERP components, Pearson correlations examined associations between changes in these components and changes in behavioral performance across all participants. The level of statistical significance was set to P < 0.05. Effect sizes were considered small, medium, and large at η2 ≥ 0.01, η2 ≥ 0.06, and η2 ≥ 0.14, respectively.

RESULTS

Two male participants from CON terminated the study prematurely because of personal reasons, so that data from 42 participants remained for analyses. As shown in Table 1, there were no baseline differences between groups in anthropometrics, intelligence, psychopathology, socioeconomic status, and physical activity levels. The compliance of the MAG was high, given that participants completed 89.7% (SD = 5.8%) of the scheduled exercise sessions. The ratings on the RPE scale (M = 13.3, SD = 0.9) immediately after judo training indicated a moderate intensity of the sessions. Based on parental report, two participants (MAG: n = 1; CON: n = 1) started another sports activity (with a weekly dose of 60 min) that was not related to the intervention during the stud period. MAG and CON both improved MABC-2 overall score (F(1,40) = 18.44, P < 0.001, η2 = 0.32) with no group differences in gains as indicated by a lack of a time–group interaction (F(1,40) = 0.23, P = 0.635, η2 = 0.01; Table 2). Moreover, there was no change in PWC170, given the lack of both a time main effect (F(1,40) = 0.39, P = 0.532, η2 = 0.01) and a time–group interaction (F(1,40) = 3.27, P = 0.078, η2 = 0.08; Table 2).

TABLE 1 - Comparison of anthropometrics, intelligence, psychopathology, socioeconomic status, and physical activity levels between the MAG and the CON at baseline.
MAG (n = 9 f/13 m) CON (n = 10 f/10 m) F P η 2
M SD M SD
Age, yr 10.3 1.2 10.7 1.5 0.82 0.372 0.02
Weight, kg 38.1 7.7 41.2 13.9 0.84 0.366 0.02
BMI, kg·m−2 17.7 2.3 18.2 3.5 0.35 0.558 0.01
IDS-2 screening 5.9 2.9 6.0 3.2 0.01 0.927 <0.01
SDQ score 10.6 4.3 11.0 4.1 0.08 0.783 <0.01
FAS score 6.2 1.6 6.6 1.6 0.43 0.518 0.01
MVPA, min·d−1 34.8 20.0 33.6 21.9 0.03 0.854 0.01
BMI, body mass index; FAS, Family Affluence Scale; IDS-2, value points on screening items of the Intelligence and Development Scales-2; MVPA = Moderate-to-vigorous physical activity; SDQ, Strengths and Difficulties Questionnaire.

TABLE 2 - Means and SD of motor skills and relative power output of the MAG and the CON at baseline and follow-up assessments.
MAG (n = 9 f/13 m) CON (n = 10 f/10 m)
Baseline Follow-Up Baseline Follow-Up
M SD M SD M SD M SD
MABC-2 overall score 48.14 26.99 60.45 27.91 56.85 24.24 66.70 27.32
PWC170, W·kg−1 2.07 0.48 2.17 0.47 2.01 0.40 1.96 0.40

With regard to behavioral performance, there were main effects of time (adjusted for changes in Go reaction time) on both commission (F(1,39) = 32.0, P < 0.001, η2 = 0.45) and omission error rates (F(1,39) = 10.9, P = 0.002, η2 = 0.22), indicating lower error rates at follow-up compared with baseline across all participants. For commission error rate, this main effect was superseded by a time–group interaction (adjusted for changes in Go reaction time; F(1,39) = 6.3, P = 0.017, η2 = 0.14), which supported that over the intervention period, MAG decreased error rates on NoGo trials to a greater extent than CON (Table 3).

TABLE 3 - Means and SD of behavioral and neurocognitive indices of the Go/NoGo task of the MAG and the CON at baseline and follow-up assessments.
MAG (n = 9 f/13 m) CON (n = 10 f/10 m)
Baseline Follow-Up Baseline Follow-Up
M SD M SD M SD M SD
Commission ER, % 25.3 15.5 15.0 15.3 29.3 15.5 25.8 15.2
Omission ER, % 3.6 3.6 1.7 2.2 4.5 5.5 2.0 3.3
Go reaction time, ms 471.7 55.7 469.1 50.5 461.5 61.5 451.3 55.6
No N2 amplitude, μV −2.1 3.4 −3.8 4.9 −0.9 6.3 1.1 6.5
Go N2 amplitude, μV −2.6 3.1 −2.6 4.0 −0.3 4.4 0.4 4.1
P3a amplitude, μV a 9.1 5.0 11.0 6.3 8.4 4.1 11.0 6.5
P3b amplitude, μV b 12.1 5.3 12.3 6.7 12.3 5.5 13.4 5.2
aAssessed from NoGo trials.
bAssessed from Go trials.
ER, error rate.

For neurocognitive indices, repeated-measures ANOVA revealed a main effect of time on P3a amplitude (F(1,40)=4.5, P < 0.001, η2 = 0.10), so that participants showed a greater amplitude at follow-up compared with baseline assessment. Moreover, there was a time–group interaction for N2 amplitude (F(1,40) = 6.0, P = 0.019, η2 = 0.13), indicating a higher increase of the negativity of this component over the intervention period in MAG compared with CON (Fig. 1). Based on correlational analysis of change scores, a higher increase of the negativity of the N2 amplitude was related to higher decrease of the commission error rate (r = 0.31; SE = 0.11; P = 0.049). In contrast, no correlations between changes in N2 amplitude and changes in Go reaction time and/or omission error rate were found.

FIGURE 1
FIGURE 1:
ERP waveforms elicited by Go (gray line) and NoGo trials (black line) and the topographic distribution of the N2, P3a, and P3b components at baseline and follow-up assessments within the MAG and the CON. Notes: The topographical distribution of the N2 and P3a/b components is based on the mean amplitude in the latency range marked by the vertical gray bar.

DISCUSSION

As indexed by changes in both behavioral and neurocognitive measures, the judo training program elicited benefits for response inhibition. With regard to performance on the Go/NoGo task, a greater reduction of the commission error rate from baseline to follow-up was found in MAG compared with CON. This result was not due to a speed–accuracy trade-off, given that changes in Go reaction time were accounted for. The judo training also increased the negativity of the N2 amplitude, indicating more effective conflict monitoring in MAG than CON after the intervention period. In contrast, the groups did not differ with respect to changes in P3a and P3b amplitudes from baseline to follow-up.

Previous meta-analyses have shown that exercise benefits executive function and inhibitory control in particular among children and adolescents (14,15). As the experimental studies that contributed to these observations focused on interference control, the present findings extend prior research by showing the sensitivity of response inhibition to a structured exercise program. However, the observed reduction of commission error rates seems to be specific to the judo intervention, because no performance changes on variants of the Go/NoGo task were found after sports activities that primarily targeted improvements in cardiorespiratory fitness (39,40). This might be explained by the absence of a mediating role of cardiorespiratory fitness on the association between exercise and inhibitory control in children and adolescents (11,41). In contrast, gains in motor skills after an exercise intervention that induced both cognitive and coordinative challenges have been found to influence benefits for this aspect of executive function (42). Although these demands were also inherent parts of the judo program, the fact that there was no group difference in the development of both MABC-2 scores and PWC170 contradicts a possible mediation of improvements in response inhibition by motor skills and/or cardiorespiratory fitness. The absence of judo-induced improvements in these aspects was not expected, given that this type of martial arts is known to elicit enhancements in general and sports-specific motor abilities (43). Consequently, it seems that the positive influence of judo on response inhibition can be detected independent from or before improvements in motor skills and cardiorespiratory fitness.

Based on the specific characteristics of judo, it is possible that improvements in behavioral performance on the Go/NoGo task were driven by psychological demands. There is an educational component of judo that seeks to increase the athlete’s sensitivity to values, such as responsibility, righteousness, patience, lowliness, courage, and kindness. Paying attention to these values when facing an opponent in judo-specific combat situations requires a reasonable amount of self-regulation. In this respect, a conceptual model suggests that regular engagement in structured exercise is considered to not only demand but also train self-control resources, which in turn translates into improved executive function by a favorable alteration of self-regulation (44). In this model, effort is understood as a shared resource of executive function and self-regulation in demanding situations that require the maintenance or change of behavior. As response inhibition is an integral part of top-down control of self-regulation (45,46), the reduced commission error rate in MAG might partly be attributed to the promotion of this resource by training martial arts (12).

Further insights into the mechanisms underlying improved behavioral performance after judo training are provided by the ERP findings. Whereas changes in P3a and P3b amplitudes did not differ between groups, MAG showed a more pronounced increase of the negativity of the NoGo N2 amplitude compared with CON. This increase from baseline to follow-up was moderately correlated with a reduction of commission error rate. The present findings therefore support the previously observed link between higher N2 negativity on trials demanding response inhibition and better behavioral performance (47). Based on the functional significance of the N2, the observed pattern of changes in MAG may reflect more effective monitoring of the concurrent and competing coactivation of response representations (22). A contribution of this process is comprehensible because conflict needs to be detected to allow for subsequent adjustments in behavior by recruiting necessary and/or additional neural resources (20). The direction of the effect of judo training differs from the limited cross-sectional evidence showing lower negativity of the N2 amplitude in high-fit compared with low-fit children (27,28). However, this pattern of results was similar for trials with low and high inhibitory demand, and its correlation with behavioral performance has not been examined. In the present study, the judo intervention elicited an increase of the negativity of the NoGo N2 amplitude only, which could be understood as a more focused recruitment of neural resources to monitor conflict in trials that actually impose a response conflict.

Moreover, a greater negativity of the N2 amplitude is one important characteristic of the neurocognitive profile found in athletes experienced in martial arts and related combat sports (29,31). Given that changes in this ERP component were detected after only 3 months, an adaptation in conflict monitoring seems to be an early response of cognitive control to regular judo training in preadolescent children. This process could have been triggered by the judo-specific combat training (“Randori”), which was an integral part of the intervention in the MAG. Randori refers to a one-on-one sparring that requires participants to attack, resist, and counter each other’s techniques, thus placing high demands on the anticipation of movements and the detection of feints. As these abilities are performed under time pressure, there is a high likeliness for competing response options. As the N2 indexes the monitoring of the simultaneous activations of such response options, its increased negativity in the MAG might have been a consequence of the repeated exposition to combat situations, in which the outcome is partly determined by this process.

In contrast to the N2 component, the P3a and P3b amplitudes did not show group-specific changes from baseline to follow-up. This is in conflict with the few previous randomized controlled trials that reported increased P3b on an interference control task after aerobic training as well as combined aerobic and coordinative training in children and adolescents (25,26). In addition to differences between these interventions and the judo training, specific contributions of the P3b to dissociable types of inhibitory control might partly account for such discrepancy. Whereas the P3b amplitude is considered to be proportional to the level of interference control required by the task, the NoGo effect is specific to the amplitude of the P3a (21). As the judo training only improved error rate on trials demanding response inhibition, changes in the ERP components sensitive to this NoGo effect were expected. However, the present findings only support a general increase of P3a amplitude over the intervention period across groups. This could partly be explained by learning effects because practice of the Go/NoGo task has been found to increase the amplitude of this component even after a short trainings session of about 40 min (48). Evidence in support of this assumption is provided by the decrease of both commission and omission error rates from baseline to follow-up in both groups. An alternative explanation takes the participants’ motivation into account, as experimental manipulations have revealed an almost linear relation of this aspect with the P3a amplitude on NoGo trials (49). Although motivation was not assessed in the present study, MAG and CON both showed a high motivation to perform well at follow-up because they knew of the opportunity to receive feedback on all measurements after the final laboratory test.

The present findings provide first insights into the effects of judo training on response inhibition and one of its underlying neurocognitive mechanisms, but the findings should be interpreted with caution because of some study-specific limitations. First, the moderate correlation between changes in behavioral performance and N2 amplitude suggests that a facilitation of conflict monitoring is not the only pathway by which judo training enhanced response inhibition. However, other neurobiological, psychosocial and behavioral mechanisms that have been discussed in relation to exercise-induced improvements in executive function have not been assessed (50). Second, judo shares many but not all characteristics with other martial arts. For example, a major difference relates to the values that are usually communicated within the training session. Thus, it is unclear whether observed benefits for response inhibition can be generalized to other sports categorized as martial arts. Third, motor skills and cardiorespiratory fitness were measured with standardized tests, but not with judo-specific measurement tools. Consequently, the lack of group differences is limited to the constructs assessed by these instruments. Nonetheless, judo should not be considered inefficient for the promotion of motor skills and cardiorespiratory fitness in general, because it cannot be ruled out that a greater dose (higher frequency or longer intervention duration) is required to elicit changes in both domains. Moreover, despite the validity of the PWC170 (37), it should be noted that it serves as a submaximal test of cardiorespiratory fitness and premature termination of the test might indicate a loss of motivation rather than the actual fitness level. Fourth, the small sample size requires groups that are comparable in variables that are related to the outcome. Although groups did not differ in socioeconomic status, intelligence, psychopathology, and other variables, it cannot be excluded that the observed changes in MAG were partly influenced by other confounders, such as pubertal status.

CONCLUSIONS

Regular engagement in judo training over 3 months improved response inhibition in preadolescent children. An increase toward more effective conflict monitoring indicated by increased negativity of the N2 might have partly accounted for the cognitively enhancing effect of judo, because changes in this cognitive control process were moderately related to improved behavioral performance. In contrast, stimulus evaluation and attentional processes indexed by P3a and P3b were not influenced by the judo intervention. Improvements in both behavioral and neurocognitive measures of response inhibition seem to be early adaptations to regular engagement in judo that occur independent from gains in motor skills and cardiorespiratory fitness.

This work was supported by the Opo-Foundation (2018-0039) and Freiwillige Akademische Gesellschaft Basel (2018-11). The funders were not involved in the conceptualization and conduct of the study.

The authors do not have any conflict of interest to declare relative to the present study. The results of the present study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation and do not constitute endorsement by American College of Sports Medicine.

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Keywords:

EVENT-RELATED POTENTIALS; GO/NOGO TASK; N200; P300; MARTIAL ARTS

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