Impact of a Mental Fatigue Protocol on Performance in Extreme Conditioning Programs

doi:10.21203/rs.3.rs-4835875/v1

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Impact of a Mental Fatigue Protocol on Performance in Extreme Conditioning Programs

https://doi.org/10.21203/rs.3.rs-4835875/v1

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The aim of this study was to assess whether mental fatigue can influence the perception of effort and the performance of individuals engaged in extreme conditioning programs. A cross-sectional, experimental, and randomized study was conducted with 25 CrossFit® practitioners randomly divided into two groups: Stroop Group (n = 13; 28.9 ± 4.9 years; 172 ± 0.1 cm; 74 ± 12.5 kg; 3.4 ± 1.8 years of practice; 5.5 ± 0.5 days of training per week) and Neutral Group (n = 12; 29.8 ± 5.3 years; 168 ± 0.1 cm; 69.89 ± 16.1 kg; 2.9 ± 1.4 years of practice; 5.2 ± 0.6 days of training per week). The first group underwent a mental stress protocol using the Stroop Color and Word Test, while the second group watched a neutral content video. Subsequently, both groups performed an adapted "Angie" exercise session. The Stroop Group, after just one application of the protocol, showed increased perception of effort (p = 0.0169) and completed the exercise session in a longer time (p = 0.038), compared to the Neutral Group. The Stroop Group also presented a higher Visual Analogue Scale (VAS) score after the mental stress protocol (p = 0.0005). A single application of a mental fatigue protocol had an immediate effect on the performance of practitioners during a training session.

CrossFit®

High Intensity Functional Training

Resistance Training

Mental Fatigue

Physical Exercise

Mental fatigue, or cognitive fatigue, can be described as a psychobiological state induced by prolonged mental exertion (Van Cutsem et al., 2022), which may result in a reduction in physical performance after cognitive tasks (Ackerman & Goldsmith, 2011; Holtzer et al., 2011).

This concept has been the subject of study in various disciplines and has significant applications in the fields of education, industry, and sports, due to its intrinsic complexity and the broad impact it has on the productivity of individuals subjected to this condition (Smith et al., 2016).

In the context of sports practice, two theories can be cited that are aimed at understanding the reasons for the reduction in performance when mental and physical activities are combined. The first theory is related to muscular fatigue, where maximal muscle strength is compromised by biochemical processes within the myocytes that hinder maximum power production, even though the task can still be executed (Bishop, 2012; Kataoka et al., 2022; Marco et al., 2017; Wan et al., 2017).

The second theory pertains to sensory perception and the synergism between the functioning of the central nervous system and the skeletal musculature. When an activity exceeds the capacity of a muscle group, the nervous system begins to activate additional muscle fibers that function synergistically with the movement, resulting in fatigue as the neural component also reaches its physical limits (Kataoka et al., 2022; Knicker et al., 2011; Meeusen et al., 2021; Pageaux & Lepers, 2018; Van Cutsem et al., 2017).

However, there is still debate concerning the relevance of mental fatigue, especially in the context of high-performance athletes. Studies often compare inactive physically individuals with those who are already well-trained, which can introduce biases in the results and make it challenging to establish a direct association between mental fatigue and performance (Staiano et al., 2019; Tornero-Aguilera et al., 2022). There is a diversity of tools available to assess the presence of mental fatigue, with some studies adopting an objective approach (Díaz-García et al., 2021).

Mental fatigue not only impairs physical performance, but also affects technique, decision-making, tactical execution, and skills in high-performance sports such as football and table tennis (Le Mansec et al., 2018; Russell et al., 2019; Smith et al., 2016). It is crucial to highlight the significant correlation between physical and mental aspects. Therefore, an athlete may possess excellent physical fitness, but still be affected by mental fatigue (Marcora et al., 2009; Van Cutsem et al., 2017).

Nonetheless, controversies still exist regarding the negative effects on athlete performance induced by mental fatigue (Brown et al., 2021; Holgado et al., 2020). The body's responses to fatigue vary depending on the individual's somatotype, training type, and energy intake, as well as potential pre-existing injuries, which can lead to localized indicators or a generalized sense of fatigue (Wan et al., 2017).

Given the increasing popularity of extreme conditioning programs (ECPs), it is essential to obtain a better understanding of the factors that can influence their practice. ECPs are training modalities characterized by a high number of repetitions and high intensity, with short or no rest intervals between sets (Lichtenstein & Jensen, 2016; Weisenthal et al., 2014).

Given the limited understanding of how mental fatigue can affect practitioners of ECPs, an integrated approach to this sports modality could contribute to advancing research in this field, with significant practical implications. This could enable the manipulation and optimization of performance among ECP practitioners, leading to direct benefits in terms of achieving the desired outcomes. Therefore, the objective of this study was to investigate the subjective perception of effort and athletic performance in individuals practicing an ECP, following the application of a mental fatigue induction protocol.

Participants

This was an experimental and randomized study involving CrossFit® practitioners. All the procedures were previously approved by the Ethics Committee for Human Research at the Universidade Federal do Triângulo Mineiro, under protocol number 4.285.963/2020. The objectives were carefully explained to all the volunteers, who subsequently signed an informed consent form, indicating their voluntary interest in participating in the research.

Recruitment of participants was performed using social media and at CrossFit® accredited training facilities in the city of Uberlândia, Minas Gerais state, Brazil.

The inclusion criteria considered individuals of both sexes, aged 18 years or older, in good health, regularly engaged in CrossFit® training for a minimum of three months, physically capable of undergoing assessments, and not concurrently participating in other sports. Non-compliance with any stage of the research was considered an exclusion criterion.

Following the sample selection process, the volunteers underwent an initial assessment to obtain information about age, height, body mass, duration of practice, and weekly training frequency. Subsequently, the participants were randomly allocated to two groups, either the Stroop Group, where they were subjected to the Stroop Color and Word Test (a mental stress test), or the Neutral Group, where they watched a video with neutral content.

Randomization was performed by placing the names of all the volunteers into an opaque envelope, after which a researcher not involved in the assessments withdrew the names and distributed them alternately into two envelopes, labeled as Stroop Group and Neutral Group.

Procedure

For comparison between the groups, assessments of performance and subjective perception of effort were conducted both before and after the implementation of the established protocol. All the assessments took place in a neutral room adjacent to a training area. The evaluation location and the training session area were equipped with good lighting and were kept at an appropriate temperature. Two trained researchers collected all the data required for the assessments. The assessment sequences are described below.

Stroop Group

The participants completed the medical history questionnaire and the informed consent form. They were then asked about their mood at that moment, which was assessed using the Visual Analog Scale (VAS) (Joyce et al., 1975). Subsequently, they were submitted to the Stroop Color and Word Test, a 3-minute test performed using a computer. This is a neuropsychological test based on experimental psychology (Jensen & Rohwer, 1966), designed to assess the ability to inhibit cognitive interference arising from the simultaneous processing of different attributes of the same stimulus. It involves the participants being challenged to perform a less automated task, such as naming the color of the ink, while suppressing interference from a more automated task, such as reading a magazine (Scarpina & Tagini, 2017; Stroop, 1935).

Next, the participants performed an Arithmetic Test, in which they were tasked with subtracting 1022 from 13, aiming to approach the result of 0 (zero) or any divisible number, within a 5-minute period, without the use of a calculator. Following completion, the VAS scale was once again administered to assess their mood at that moment.

After the induced stress, the volunteers performed an adapted "Angie" benchmark workout, using a stopwatch system. They were required to perform 50 repetitions of pull-ups, 50 repetitions of push-ups, 50 repetitions of sit-ups, and 50 repetitions of air-squats. Times were recorded at the end of each exercise and on completing the entire set.

Finally, the perception of effort was assessed using the Borg Scale (Alsamir Tibana et al., 2019; Borg, 1970; Morishita et al., 2018), developed based on heart rate variables that increase with exercise intensity. This is a scale ranging from very light activity to maximum exertion, where individuals mark the score corresponding to their perception of effort at that moment.

Neutral Group

The participants completed the medical history questionnaire and the informed consent form, after which they were asked about their mood at that moment, applying the VAS. Subsequently, they watched a neutral content video about the history of aviation, which lasted approximately 10 minutes: https://www.youtube.com/watch?v=tDTdqWH-2VA. At the end of the video, the VAS was again applied to assess their mood at that moment. Following this, in the same way as the Stroop Group, they performed the adapted benchmark "Angie" workout, using a stopwatch system, completing 50 repetitions of pull-ups, 50 repetitions of push-ups, 50 repetitions of sit-ups, and 50 repetitions of air-squats. Times were recorded at the end of each exercise and on completing the entire set.

Statistical Analysis

The results were firstly obtained separately for each group and were presented as means and standard deviations. The Shapiro-Wilk test was applied to assess data normality. When the results were normally distributed, comparison of the variables within and between the groups employed the unpaired t-test, while the Mann-Whitney test was applied when the results did not follow a normal distribution. A statistical significance level of p < 0.05 was adopted in all the analyses. Additionally, the effect size was estimated using Hedge's G index, with the following classification for interpretation of effects: 0.20–0.49 (small), 0.50–0.79 (moderate), and ≥ 0.80 (large).

A total of 25 volunteers were assessed, with 12 in the Neutral Group and 13 in the Stroop Group. Participant characterization data are presented in Table 1. No significant differences were observed between the groups in terms of sample characteristics.

Table 1. Characterization of the volunteers.

	Neutral Group (n = 12)	Stroop Group (n = 13)	p-value
Age (years)	29.8 ± 5.3	28.9 ± 4.9	0.46
Height (cm)	168 ± 0.1	172 ± 0.1	0.19
Body mass (kg)	69.8 ± 16.1	74 ± 12.5	0.30
Duration of practice (years)	2.9 ± 1.4	3.4 ± 1.8	0.63
Weekly training frequency (days)	5.2 ± 0.6	5.5 ± 0.5	0.39

Table 2 presents the results for the variables related to the subjective perception of effort. The VAS values obtained prior to the intervention showed no significant differences between the groups. Within-group analysis, comparing the VAS values before and after the intervention, revealed a significant difference only for the Stroop Group (p = 0.0005).

Between-group analysis showed a significant difference in the Borg Scale results, with higher values for the Stroop Group, compared to the Neutral Group (p = 0.0169). A significant difference was also observed for total time in performance of the air-squat exercise, with the Stroop Group taking more time than the Neutral Group (Table 2).

	Neutral Group (n = 12)	Stroop Group (n = 13)	p-value	Hedge’s G
Initial VAS	3.2 ± 1.8	2.6 ± 1.2	0.40	0.39
Final VAS	2.8 ± 1.7	6.2 ± 2.4*	0.001	1.62
Borg Scale	14.1 ± 1.9	16 ± 1.3	0.016^†	1.17
Air-squat execution time	552.7 ± 81.2	660.3 ± 195.9	0.038^†	0.71

Table 2. Results obtained for the subjective perception of effort assessments and performance in the air-squat exercise (mean ± SD).

VAS: Visual Analog Scale. *Significant intra-group difference for the VAS (initial vs. final values). ^†Significant difference between groups.

The aim of this study was to investigate whether mental fatigue, induced by a protocol consisting of 3 minutes of the Stroop Color and Word Test and 5 minutes of the Arithmetic Test, followed by execution of the benchmark workout (Angie) with 50 repetitions each of pull-up, push-up, sit-up, and air-squat exercises in a timed setting, had the potential to affect the performance of CrossFit® practitioners.

The results indicated that mental fatigue led to a significant increase in the perception of effort among the Stroop Group participants. This effect was not observed in the Neutral Group. Significant differences in VAS were only observed after implementation of the proposed protocol, demonstrating that there was a substantial impact of mental fatigue on the performance of the participants during the training session.

The present findings were consistent with the work of Staiano et al. (2019), who identified a deterioration in the performance of kayakers after the application of mental tests that induced psychological stress, such as the Stroop Color and Word Test, when compared to a group that engaged in cognitively neutral activities.

Other studies investigated the effects of mental fatigue in the sports activities of running, swimming, and kayaking, with 2%, 5%, and 1.2% slower times achieved by participants, respectively, when compared to control groups that were not subjected to cognitive stress (MacMahon et al., 2014; Pageaux & Lepers, 2018; Penna et al., 2018). These findings reinforce the hypothesis that the psychological component plays an important role in the performance of athletes. In this study, performance (measured in seconds) in the air-squat exercise was nearly 20% poorer for the Stroop Group.

In studies that were able to assess the physiological response of individuals during activities following a period of mental fatigue, variations in biochemical and physiological parameters of the body were identified in response to mental stress. Mental fatigue impairs performance in activities that require endurance, motor skills, and decision-making, but it should be emphasized that muscular strength is not affected in the presence of mental fatigue (Pageaux & Lepers, 2018). Further experimental evidence to support this effect was reported by Marcora et al. (2009), who concluded that mental fatigue limits exercise tolerance, mainly due to an increased perception of effort.

Since the noradrenergic system plays a role in accelerating central fatigue during prolonged exercise, there are changes in perceived effort that are related to alterations in the concentrations of neurotransmitters such as dopamine and adenosine (Meeusen et al., 2021). These changes occur in various brain regions, including the prefrontal cortex and the anterior cingulate cortex.

Stress, whether physical or mental, can significantly affect the physiological systems of athletes, in some cases resulting in injuries and the inability to continue training. A recent study investigated the prevalence of injuries in CrossFit® practitioners by applying the Musculoskeletal Injury-Focused Sports Readiness Questionnaire (Neto et al., 2022). Evaluation of 368 practitioners of this sport found an injury rate of 48.91%, with higher prevalence of injuries in the shoulder girdle, lumbar spine, and knees. These injuries were associated with training duration and joint overload (Neto et al., 2022).

It has also been shown that a single session of a CrossFit® protocol was sufficient to induce changes in jump height, mean power, and maximum speed (Maté-Muñoz et al., 2017), as well as alterations in overhead squat mechanics (Neto et al., 2023), regardless of whether the participants were exposed to a mental fatigue protocol.

The aim of the present work was to fill a gap in the literature by seeking to improve knowledge of the physical and mental processes involved in extreme conditioning programs (ECPs). The results highlight the importance of better understanding individuals who practice this sports modality, since this can be crucial for instructors responsible for designing progressive training programs, especially for beginners. This aligns with the need for musculoskeletal preparation for physical effort, as there is evidence that mental stress can lead to muscular pain (Brown et al., 2021; Mehta & Agnew, 2012; Mehta & Parasuraman, 2014; Salvagioni et al., 2017).

ECPs require athletes to perform both physical and mental actions. The activity requires strength, power, muscle flexibility, and agility. Additionally, athletes must manage time and the number of repetitions in each exercise, according to the goals set for the day's training, known as the Workout of the Day (WOD). Competition among athletes often extends beyond external competition; it also involves internal competition, where individuals seek to surpass their own limits each day. Therefore, any interference during training can have a significant impact on performance.

This study identified a decrease in exercise performance after the application of a mental stress protocol, suggesting the need for further investigations to address other related questions. It would be important to undertake assessments of physiological, biochemical, and biomechanical parameters, which were limitations of this study, to confirm and expand on the results obtained regarding performance and the subjective perception of effort. Such assessments could contribute to a better understanding of the effects of mental fatigue in the context of ECPs.

A single application of a mental fatigue protocol was demonstrated to exert an immediate effect by increasing the perception of effort and the time required to complete an exercise session, thereby reducing the performance of the practitioner.

Author Contribution

Vinícius Jordão Silva: Preparing the project; selecting the volunteers; carrying out the evaluations; analyzing the results; writing the article.Antônio Ribeiro Neto: Analyzing the results; discussing the results; writing the article.Douglas Felipe de Sousa: Analyzing the results; discussing the results; writing the article.Gladson Ricardo Flor Bertolini: Writing project; analyzing results; writing the article .Dernival Bertoncello: Writing the project; evaluating the volunteers; analyzing the results; discussing the results; writing the article.

Disclosure statement

The authors report that there are no potential conflicts of interest regarding this work.

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No competing interests reported.

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Impact of a Mental Fatigue Protocol on Performance in Extreme Conditioning Programs

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