Acute Effects of a Single-Bout Session of High-Intensity Functional Training and Moderate-Intensity Functional Training on Cognitive Functions, Anxiety, and Stress in Healthy Adults

Abstract

Background: Currently, it has been observed that a fast-paced lifestyle, along with factors such as work pressure and economic and political uncertainty, among others, negatively impacts cognitive functions and increases levels of anxiety and stress in the population. In this context, physical exercise has been shown to be an effective means of alleviating these effects. The aim of this study is to analyze the acute effects of a single-bout session of high-intensity functional training (HIFT) and a single-bout session of moderate-intensity functional training (MIFT) on cognitive functions and psychological responses such as anxiety and stress. Methods: The study presents an experimental design with an analytical approach, involving 57 healthy adults in a 30 min functional exercise circuit. The HIFT group, with 28 participants, performed a high-intensity exercise circuit (>85% HR max). The MIFT group, with 29 participants, performed a moderate-intensity exercise circuit (70–80% HR max). To evaluate the dependent variables of executive function, attention, memory, anxiety, and stress, the Stroop Test, d2 Test, Word-Recall Test, STAI, and PSS were used, respectively. These tests were administered, in the order mentioned, immediately before and immediately after the training session. Results: Both groups (HIFT and MIFT) showed significant improvements in executive function, attention, and memory, as well as significant reductions in anxiety and stress after the intervention (all p values ranged between p < 0.001 and p < 0.04). However, the HIFT group demonstrated greater improvements in cognitive function and more pronounced reductions in anxiety and stress when compared to the MIFT group. Conclusions: Both HIFT and MIFT can improve cognitive function and reduce anxiety and stress, but high-intensity exercise appears to offer greater benefits.

1. Introduction

Currently, it has been demonstrated that the fast-paced lifestyle we are subjected to, combined with work pressure, lack of sleep, and chronic stress, as well as a sedentary lifestyle and excessive use of technology, negatively affect cognitive function [1,2]. Various specific treatments, such as physical exercise, have resulted in improvements in cognitive functions [3]. These cognitive functions involve the mental processes that allow us to receive, select, store, transform, develop, and retrieve information that we have received through external stimuli. Functions such as perception, attention, and memory enable us to understand and relate to the world more effectively [4].

On the other hand, 27.4% of the global population suffers from mental health problems, with anxiety disorders, affecting 6.7% of individuals, being the most common [5]. Other prevalent disorders today include depression, adjustment reactions, and sleep disorders [6]. In general terms, anxiety is understood as an emotional response to a threat, manifested at cognitive, emotional, physiological, and motor levels [7]. It can consist of two dimensions: trait anxiety and state anxiety, with the former being a personality trait, and the latter representing the current state of the individual [8]. Anxiety is often associated with stress, which arises from the individual’s inability to cope with external demands (environment) generated by overwhelming situations, and it can sometimes lead to serious psychological disorders [7].

Factors such as economic crises, political uncertainty, work-related stress, and time pressures increase stress and anxiety, which, in turn, impact emotional and physical health [6]. These issues are exacerbated by the constant use of technological devices, which encourage prolonged periods of inactivity, such as working at a computer or spending leisure time in front of screens [9]. Physical inactivity has become the fourth leading risk factor for global mortality and is associated with a 20% to 30% increase in mortality rates compared to those for people who engage in regular physical activity [10].

The World Health Organization (WHO) defines mental health as a state of well-being in which individuals are aware of their abilities, cope with the normal stresses of life, work productively, and contribute to their community. At the beginning of the 21st century, concern for mental health increased, with the recognition that mental disorders, affecting over 450 million people, are the leading causes of disability worldwide. The focus on positive mental health and positive psychology has gained importance, extending the definition of well-being beyond the mere absence of disease and promoting the development of cognitive and emotional resources to face challenges and achieve goals [11]. This organization adopts a comprehensive approach to mental health, encompassing the promotion of well-being and the prevention and treatment of mental disorders, while highlighting the impact of prolonged stress on cognitive functions such as memory, concentration, and mental processing [3]. In the workplace, mental well-being is crucial for both health and performance, making it essential to foster healthy work environments that reduce stress and improve rest [12]. Additionally, anxiety disorders, considered a silent epidemic of the 21st century, are driven by factors such as digital hyperconnectivity, information overload, climate change, and political polarization, which significantly increase anxiety levels, necessitating psychological therapy, lifestyle changes, and a deep understanding of the underlying causes for effective treatment [13].

Variables such as optimism, resilience, gratitude, and mindfulness have a positive impact on mental health. Optimism is associated with lower levels of depression and anxiety. Resilience protects against stress and helps in coping with adverse situations. Gratitude and mindfulness enhance well-being and reduce stress levels [11]. Various specific treatments, such as physical exercise, have resulted in improvements in cognitive functions [3].

Physical activity is associated with better mental health. A study conducted in Madrid demonstrated that high or moderate levels of physical activity are associated with better mental health; physical activity reduces symptoms of depression and anxiety, improves resilience, and increases life satisfaction [14]. In Bogotá, students with low levels of physical activity exhibited lower resilience and life satisfaction [15].

Physical exercise has been shown to improve cognitive aspects in healthy adults. HIIT (high-intensity interval training) programs demonstrate benefits, although studies report mixed results [16,17,18,19]. Moderate-intensity aerobic exercise shows positive effects on cognitive function [20,21]. High-intensity functional training (HIFT) and moderate-intensity functional training (MIFT) are both functional training methods based on exercises that can be adapted to any fitness level, aiming to improve an individual’s functionality and work capacity [22,23]. Specifically, HIFT differs from high-intensity interval training (HIIT) in its use of functional and varied exercises with differing durations of activity, which may or may not include rest intervals—a feature that is consistently present in HIIT [22]. Regarding the evidence on the effects of HIFT on cognitive functions, studies have shown that it can improve response speed, as well as accuracy, in cognitive tasks, such as those assessed through the Stroop Test [24].

The aim of the present study, therefore, is to analyze the acute effects of single-bout HIFT training on selective attention, executive function, working memory, anxiety, and stress, compared to those of single-bout MIFT training in healthy adults. We hypothesize that after completing the HIFT, there will be improvements in cognitive function, specifically attention, memory, executive function, and psychological responses to stress, and that anxiety will be lower in healthy adults, compared to the results obtained from the MIFT.

2. Materials and Methods

2.1. Design and Participants

The present study consisted of a randomized controlled trial (RCT) that analyzed the effects of two different single bouts of training (HIFT and MIFT). The study was conducted on the second Friday of February, 2024.

All participants, who trained at the WftHealthandfitness training center in Pizarra (Málaga, Spain), were contacted in person, by phone (via WhatsApp and phone calls), and through social media. Out of a total of 71 individuals initially contacted, 57 completed the session and the tests. The reasons for not completing the session and tests were as follows: busy (n = 5), living too far (n = 4), did not complete the training (n = 2), and did not perform the post-test (n = 3). Finally, 28 participants were included the HIFT group, and 29 were part of the MIFT group. (see Figure 1). Regarding the inclusion criteria, participants had to be over 18 years old, have no functional or vestibular pathologies, and be able to understand the instructions, exercises, and protocols of this project. Exclusion criteria included conditions that contraindicated physical testing, diseases that could alter functional activity (such as vestibular disorders), psychiatric or neurological disorders, systemic diseases (e.g., diabetes mellitus, cancer, or cardiovascular conditions), or participants already enrolled in another rehabilitation program.

This study was approved by the Local Human Ethics Committee (006/PE/TS/2023), in accordance with the Declaration of Helsinki [25], good clinical practices, and applicable laws and regulations, as well as with the Ethical Standards in Scientific Research in Sport and Exercise [26]. Informed consent was obtained from all individual participants included in the study.

Once the informed consent was signed, participants underwent an initial assessment, then participated in the intervention session of the study. Upon completion of the session, the acute effects of the training session were evaluated. All procedures were conducted by a physical activity professional who assessed the baseline stages prior to the intervention and the acute responses after the intervention.

2.1.1. Variables

Descriptive data collection and anthropometric measurements.

Descriptive data were collected through personal interviews using a specific questionnaire covering sociodemographic characteristics. The measurement of body height was performed with a stadiometer to the nearest 0.1 cm. The measurement of body weight was performed with a calibrated weight scale to the nearest 0.1 kg [27].

2.1.2. Executive Function

To assess executive function, the Stroop Test (executive function, selective attention) was used. The Stroop Test application presented a list of words with colors that either matched the word (congruent, e.g., the word “red” displayed in red) or did not match the word (incongruent, e.g., the word “red” displayed in blue) before and after the exercise session [28]. The test measures the speed and accuracy of participants’ responses using specific indicators: STROOP-FC (fastest correct response time), STROOP-MTQ (average time per question), STROOP-MTA (average time per correct response), and STROOP-CR (number of correct responses). These parameters allow for a detailed evaluation of the processing capacity in tasks involving cognitive interference. This test has shown an internal consistency of Cronbach’s alpha 0.77 and an average reliability coefficient of r = 0.85 [29].

2.1.3. Attention

To assess attention and concentration, the d2 Test (selective attention and concentration) was used. The d2 is a timed test designed to measure selective attention. It evaluates processing speed, adherence to instructions, and performance on a task that involves discriminating between visually similar stimuli, thereby allowing for an estimation of a person’s attention and concentration, applicable to individuals aged 8 to 60. The test consists of carefully scanning each line from left to right and marking every “d” that has two small dashes (either both above, both below, or one above and one below). In the manual, these elements (i.e., correct stimuli) are referred to as “relevant elements.” The other combinations (“p”, with or without dashes, and “d”, with one or no dashes) are considered “irrelevant”, as they should not be marked. The questionnaire consists of 14 lines, and each line was presented for 20 s. The test generates the following scores: total processed stimuli/responses, total correct responses, commissions, which refer to the total number of irrelevant elements mistakenly marked as correct, and omissions, representing the number of relevant elements the participant failed to detect. The total attention score (D2 TOT) is calculated as the total number of processed stimuli minus the sum of omissions and commissions. The concentration index (D2 CON) is derived from subtracting the number of commissions from the total correct responses. Additionally, the metrics include the line with the highest number and the line with the lowest number of processed stimuli. The variation index (D2 VAR) is calculated by the difference between the most processed line and the least processed line. In terms of the internal consistency of the instrument, it presents a Cronbach’s alpha > 0.90 [30].

2.1.4. Memory

Regarding memory, it was assessed using the Word Recall test (verbal learning, delayed declarative memory), which consists of a memory test with a list of 10 words. The participants were shown the words on the list with a 1 s interval between each, and after 60 s—during which they engaged in unrelated conversation—they were asked to write down the words they remembered. The score was calculated by recording the number of words recalled in each of the tests performed. Higher scores are interpreted as a better level of memory [31].

2.1.5. Anxiety

Two levels of anxiety were measured using the State-Trait Anxiety Inventory (STAI) questionnaire. The questionnaire consists of 40 items, 20 pertaining to state anxiety and 20 to trait anxiety. State anxiety (S-A) is conceptualized as a transient emotional condition of the human organism, characterized by consciously perceived subjective feelings of tension and apprehension, as well as hyperactivity of the autonomic nervous system. It can vary over time and fluctuate in intensity. Trait anxiety (T-A), on the other hand, refers to a relatively stable anxious disposition in which individuals differ in their tendency to perceive situations as threatening, leading to an increase in state anxiety. Anxiety levels were measured using a four-point Likert scale (0 = not at all to 3 = very much). Finally, it is important to note that some of the 40 questions are reversed, while others are direct. For trait anxiety, there are 7 reversed items (21, 26, 27, 30, 33, 36, 39) and 13 direct items (22, 23, 24, 25, 28, 29, 31, 32, 34, 35, 37, 38, 40). For state anxiety, there are 10 reversed items (1, 2, 5, 8, 10, 11, 15, 16, 19, 20) and 10 direct items (3, 4, 6, 7, 9, 12, 13, 14, 17, 18). Reversed items are scored inversely, where 0 becomes 3, 1 becomes 2, 2 becomes 1, and 3 becomes 0. The total score for each concept ranges from 0 to 60 points, with higher scores indicating greater anxiety [32]. As for the reliability of the questionnaire, Cronbach’s alpha scores of 0.90 were observed for trait anxiety and 0.93 for state anxiety [33].

2.1.6. Stress

Stress levels were assessed using the Perceived Stress Scale (PSS), a self-reporting instrument that evaluates the level of perceived stress during the past month. It consists of 14 items with responses on a five-point Likert scale (0 = never, 1 = almost never, 2 = sometimes, 3 = often, 4 = very often). The total PSS score was calculated by reversing the scores for items 4, 5, 6, 7, 9, 10, and 13 (i.e., 0 = 4, 1 = 3, 2 = 2, 3 = 1, and 4 = 0) and then summing the 14 items. The raw score indicated that a higher score corresponds to a higher level of perceived stress [34]. The internal consistency reliability and factorial validity of the questionnaire in its Spanish version are adequate, with a Cronbach’s alpha of 0.81 [35].

2.1.7. Intervention

Participants were informed about the study one month in advance. After agreeing to participate, they were randomly assigned to a group and provided with the corresponding dates for the intervention. Participants were notified via direct contact 48 h before the intervention and were provided with the Uptivo Bridge Cloud heart rate monitor (Uptivo, S.r.l, Carate Brianza, Italy) [36], which they had to sync with their mobile phones. Additionally, they were added to a WhatsApp group, in which the procedure was explained. At the time of the intervention, forms and questionnaires were provided through the WhatsApp group. Both groups were randomly assigned using the 1:1 method. In both the HIFT and MIFT groups, all measurements were performed right before the start of the intervention, and the results were immediately recorded in a data log afterward. The study was approved by the Ethics Committee of the University of Wales and Trinity Saint David (006/PE/TS/2023).

Participants were asked to arrive half an hour early to complete the initial tests. After the initial assessment, they were randomly and simply divided into two groups, i.e., participants included in the study were randomly assigned to a high-intensity functional interval training group (HIFT group) or to a moderate intensity functional interval training (MIFT group) in a 1:1 ratio using a computer-generated table of numbers. The HIFT group performed 30 min of high-intensity functional training (>85% max. HR), consisting of a circuit of the following functional exercises: lunges, push-ups, jump squats, suspension rows, planks, and burpees (Figure 2). This circuit was divided into 30”-10” blocks, six rounds, with 1 min rest periods between rounds. The MIFT group performed the same circuit as the HIFT group for 30 min, but at a lower intensity (70–80% max. HR). Both groups were monitored at all times to ensure that they reached the target intensity using the Uptivo Bridge Cloud heart rate monitor (Uptivo, S.r.l, Carate Brianza, Italy). This device allowed us to determine whether the participants were within the required % of HR. If they momentarily exceeded or fell short of the target, they would be able to adjust the intensity to reach it. Afterward, the participants were re-assessed.

2.1.8. Statistical Analyses

The data were analyzed using the SPSS v.21.0 statistical software for Windows (SPSS Inc., Chicago, IL, USA), with the level of statistical significance set at p < 0.05. The Kolmogorov–Smirnov test was used to assess the normality of the variables. Continuous variables were described using means and standard deviations, while categorical variables were described using percentages and frequencies. A single factor was used to verify the absence of statistically significant differences in pre-intervention measures. When pre-test differences were found, a univariate analysis was conducted using variance, with post-intervention measures as the dependent variable and pre-intervention measures as the covariate. Within-group differences (pre- and post-intervention values) for state and trait anxiety levels, stress, executive function, attention, and memory were assessed using Student’s t-test, following both per-protocol and intention-to-treat principles. Additionally, differences between the MIFT and HIFT groups were examined after adjusting for baseline values of body mass index, age, sex, and initial scores across all analyzed variables using analysis of covariance (ANCOVA). Finally, we calculated the effect size statistically (x ≥ 0.2 to ≤0.5 indicating a small effect size, ≥0.5 to ≤0.8 indicating a moderate effect size, and ≥0.8 indicating a large effect size) [37].

3. Results

Table 1. Descriptive information pre-intervention.

Characteristics	Total (n = 57)		HIFT (n = 28)		MIFT (n = 29)
	Mean	SD	Mean	SD	Mean	SD
Age (years)	40.56	8.91	38.78	9.06	42.27	8.57
Anthropometric measurements
Height (cm)	167.0	9.719	167.96	11.36	166.24	7.93
Weight (kg)	69.09	13.35	68.60	12.33	69.56	14.47
BMI (kg/m2)	24.85	4.82	24.67	4.91	25.29	5.01
Executive function
STROOP-FR	11.97	11.64	14.67	15.75	9.46	4.77
STROOP-MTQ	22.58	12.08	25.72	13.58	19.66	9.85
STROOP-MTA	17.60	13.42	20.08	17.37	15.30	7.94
STROOP-CR	7.50	6.97	6.10	6.29	8.86	7.44
Attention
D2 TOT	147.40	160.56	117.25	76.11	176.51	210.20
D2 CON	163.56	48.35	156.28	50.45	170.58	46.02
D2 VAR	7.29	3.11	8.14	3.66	7.17	2.45
Memory
WORD RECALL	6.29	1.28	6.10	1.39	6.48	1.15
Anxiety
STAI- State	31.42	5.54	31.42	4.58	33.37	6.27
STAI- Trait	15.63	6.34	15.42	4.75	15.82	7.57
Stress
PSS	19.70	8.64	19.75	4.75	19.65	7.97
	N	PERC. %	N	PERC. %	N	PERC. %
Male	18	31.58	11	39.29	7	24.14
Female	39	68.42	17	60.71	22	75.86
LE—No education	0	0	0	0	0	0
LE—Primary	4	7.02	3	10.71	1	3.44
LE—Secondary	29	50.88	15	53.57	14	48.28
LE—University	24	42.10	10	35.71	14	48.28

Abbreviations: HIFT (high-intensity functional training); MIFT (moderate-intensity functional training); BMI (body mass index); STROOP-FC (fastest correct response); STROOP-MTQ (mean time per question); STROOP-MTA (mean time per correct response); STROOP-CR (correct responses); D2-TOT (total); D2-CON (concentration index); D2-VAR (variability index); STAI-State (state anxiety); STAI-Trait (trait anxiety); PSS (perceived stress scale); LE (level of education), categorized as: no education, primary education, secondary education, and university education.

presents the descriptive data of the participants at baseline. A total of 57 adults (40.56 ± 8.91 years) participated in the present study. The majority of participants had an education level higher than secondary school (93%), and the mean BMI was 24.85 ± 4.82 kg/m².

In relation to cognitive function as a dependent variable, the mean number of correct responses was 11.97 ± 11.64 s in the Stroop Test overall, differing by groups: the HIFT group showed values of 14.67 ± 15.75, and the MIFT group showed values of 9.46 ± 4.77. Regarding the mean time per question, the average for both groups was 22.58 ± 12.08 s for the Stroop Test; however, the HIFT group showed values of 25.72 ± 13.58 s compared to values of 19.66 ± 9.85 s for the MIFT group. Overall, the mean time per correct response was 17.60 ± 13.42 s for the Stroop Test. The HIFT group displayed values of 20.08 ± 17.37 s, while the MIFT group showed values of 15.30 ± 7.94 s. As for the mean number of correct responses in the HIFT group, the values were 6.10 ± 6.29 correct, while in the MIFT group, they were 8.86 ± 7.44 correct. (All of this information is presented in Table 1).

Regarding the control of dependent variables, the mean score for the state anxiety test was 31.42 ± 5.54, with a mean value of 31.42 ± 4.58 in the HIFT group and a mean value of 33.37 ± 6.27 in the MIFT group. The mean score for the trait anxiety test was 15.63 ± 6.34, with a mean value of 15.42 ± 4.75 in the HIFT group and a mean value of 15.82 ± 7.57 in the MIFT group. The results for the stress test indicated a score of 19.70 ± 8.64, with the HIFT group scoring 19.75 ± 4.75 and the MIFT group scoring 19.65 ± 7.97 (see Table 1).

In the d2 Attention Test, for the attention variable, the overall mean score was 147.40 ± 160.56, with the HIFT group showing values of 117.25 ± 76.11 and the MIFT group showing 176.51 ± 210.20. For the concentration variable, the overall mean score was 163.56 ± 48.35 in the HIFT group, which had values of 156.28 ± 50.45, and 170.58 ± 46.02 in the MIFT group. Regarding the variability variable, the mean score between both groups was 7.29 ± 3.11. The HIFT group showed values of 8.14 ± 3.66, while the MIFT group showed values of 7.17 ± 2.45. In the Word Recall Test, the mean score was 6.29 ± 1.28, differing between groups; the HIFT group showed values of 6.10 ± 1.39 compared to the MIFT group, which displayed values of 6.48 ± 1.15 (see Table 1).

As shown in

Table 2. Comparison of means of the studied variables, pre- and post-intervention, based on the type of training performed.

	HIFT			MIFT
	PRE	POST	p	PRE	POST	p
Executive Function
STROOP-FR	14.67	9.26	0.188	9.46	10.11	0.522
STROOP-MTQ	25.72	18.68	0.035 *	19.66	15.25	0.035 *
STROOP-MTA	20.08	12.92	0.105	15.30	15.04	0.815
STROOP-CR	6.10	9.75	0.026 *	8.86	10.37	0.298
Attention
D2-TOT	117.25	199.03	<0.001 **	176.51	187.82	0.776
D2-CON	156.28	223.75	<0.001 **	170.58	210.79	<0.001 **
D2-VAR	8.14	6.67	0.076	7.17	7.27	0.837
Memory
WR	6.10	6.60	0.032 *	6.48	6.41	0.810
Anxiety
STAI- State	31.42	30.00	0.066	33.37	30.07	0.003 *
STAI- Trait	15.42	15.70	0.770	15.82	15.82	1.000
Stress
PSS	19.75	18.25	0.264	19.65	18.58	0.341

Abbreviatures: HIFT (high-intensity functional training); MIFT (moderate-intensity functional training); STROOP-FC (fastest correct response); STROOP-MTQ (mean time per question); STROOP-MTA (mean time per correct response); STROOP-CR (correct responses); D2-TOT effectiveness (total); D2-CON (concentration index); D2-VAR (variability index); WR (word recall/memory); STAI-State (state anxiety); STAI-Trait (trait anxiety); PSS (stress).* p < 0.05; ** p < 0.001.

, regarding executive function, no significant differences were found between the HIFT and MIFT groups in the mean time per question after the intervention. However, significant differences were observed in the interaction analysis for both groups (HIFT: t(2.235), p = 0.035; MIFT: t(2.229), p = 0.035) (Figure 3). Regarding correct responses in the Stroop Test, no significant differences were found between groups in the post-intervention phase, but significant differences were noted in the interaction analysis within the HIFT group (t(−2.358), p = 0.026). For the variable of fastest correct responses, no significant differences were found in either the covariance analysis or the interaction analysis for both groups (HIFT: t(1.353), p = 0.188; MIFT: t(−0.648), p = 0.522). Similarly, no significant differences were found in the mean time per correct response in any of the analyses (HIFT: t(1.682), p = 0.105; MIFT: t(−0.236), p = 0.815).

In the attention test, significant differences were observed in concentration after the intervention (p < 0.01), with a large effect size in both groups (HIFT: d = 2.19; MIFT: d = 1.03). The interaction analysis showed significant differences in the HIFT group (t(−11.629) p < 0.001) and in the MIFT group (t(−25.387) p < 0.001). In attention measured by the d2 Test, the interaction analysis indicated significant differences in the HIFT group (t(−9.057) p < 0.001). For variability, no significant differences were found in any of the analyses. (All of this information is presented in Table 2).

In regards to verbal learning and delayed declarative memory, no significant differences were found between groups in the post-intervention phase or in the interaction analysis (Table 2).

Regarding state anxiety, no significant differences were found between groups in the post-intervention phase, but the interaction analysis revealed significant differences in the MIFT group (t(3.330), p = 0.003). In regards to trait anxiety, no significant differences were found in any of the analyses (Table 2).

In regards to perceived stress, no significant differences were found between groups in the post-intervention phase or in the interaction analysis (Table 2).

4. Discussion

The present study aimed to analyze the acute effects of single-bout high-intensity functional training (HIFT) and moderate-intensity functional training (MIFT) on cognitive function, stress, and anxiety. The results showed significant improvements in executive function, specifically in the mean response time in both sessions, although only the HIFT group showed significant improvements in correct responses. No significant differences were observed for the other executive function variables.

In terms of attention, both groups showed significant improvements in concentration, with a large effect size. The HIFT group demonstrated improvements in both concentration and attention, while the MIFT group only showed improvements in concentration. Regarding memory, no significant differences were found for either group. For concerning anxiety, only the MIFT group showed significant improvements in state anxiety (p = 0.003), with no changes in trait anxiety or stress in either group. We would like to highlight that, throughout the discussion, due to the scarcity of scientific evidence from studies similar to that conducted in the present manuscript, we will compare and contrast our results with those from similar studies in different populations or comparable populations, as well as with interventions related to the theme of the manuscript.

Regarding HIIT, it has been associated with improvements in executive function (EF) [38,39]. A systematic review suggested that HIIT may have a positive effect on EF, with 61% of studies showing a positive effect and 39% showing no or negative effects [30]. A recent study showed improvements in attention and cognitive flexibility following a four-week HIIT program involving overweight adult women [39]. However, further research is needed to confirm these findings and explore the long-term benefits of HIIT on cognitive function. Other studies suggest the importance of identifying factors such as age, gender, and fitness level [40].

On the other hand, attention, measured using the d2 Test, showed significant improvements in the HIFT group, supported by the results of previous studies in different populations. A study with children showed improvements in attention following a 10 min HIIT training session [41]. Another study with young adults found benefits in regards to executive function and attention after HIFT and MICT (moderate-intensity continuous training) [24]. On the other hand, regarding the effects on concentration, also measured with the d2 Test, our study showed significant acute improvements after the session in the HIFT group. This result is also observed in older adults, but in this case, after a 3-month HIFT intervention, highlighting that no improvements in attention were found [42].

Regarding working memory, measured with the Word Recall Test, no significant results were found, which aligns with studies that do not show exercise effects on working memory immediately after exercise [43,44]. However, some studies have reported improvements with HIIT and MICE (moderate-intensity continuous exercise) programs [45]. Finally, we would like to highlight a study that found significant improvements in working memory after a single session of HIFT compared to the results for another group that walked at 60% of their heart rate reserve [46].

Concerning the construct of anxiety, the MIFT group showed significant improvements in state anxiety (p = 0.003), with no changes in trait anxiety in either group. This finding is also observed in previous studies that show a reduction in anxiety following exercise programs, although without considering the intensity of the exercise [47,48].

Regarding the variable of stress, no significant improvements were obtained. One study agrees with our results, as it did not show significant differences in stress following an aerobic exercise program, although the control group showed an increase in perceived stress, suggesting that exercise may prevent increases in stress [49]. Additionally, we found a study that, following an HIIT protocol, reported significant reductions in perceived stress in both the experimental and control groups, with no significant differences between them [50].

4.1. Limitations and Strengths

Regarding the limitations of our study, we can highlight that an exhaustive analysis of the current literature on the acute effects of a single-bout HIFT and MIFT training on cognitive levels, anxiety, and stress could not be conducted due to the scarcity of specific studies on the topic. Another limitation of the study was the loss of sample size, as shown in the flowchart, starting with 71 invited subjects and ending with 57 participants. In relation to this, a larger sample size would have allowed us to obtain more representative results. Finally, it should be noted that the sample presents a gender imbalance, with a significantly higher percentage of women (69.86%) compared to men (30.14%), and the age range of the participants is very broad, which could influence the generalization of the results.

Among the strengths of the study, the execution of a randomized clinical trial stands out. Furthermore, a precise intensity control system, the Uptivo Bridge Cloud heart rate monitor (Uptivo, S.r.l, Carate Brianza, Italy) [36], was utilized, ensuring the reliability of the data obtained regarding exercise intensity. Another strength of the manuscript is that it is a pioneering study, which can serve as a reference for other authors to further explore the topics and methodologies addressed throughout the study. Lastly, we want to highlight the clarity of the procedure and protocol carried out to make it replicable in different studies, allowing it to be conducted in diverse populations, regardless of age, gender, or level of training experience, as the proposed exercises can be adapted to different levels, while considering the principle of individualization.

4.2. Future Research Directions

For future research, we propose the inclusion of the measurement of brain-derived neurotrophic factor (BDNF) through analysis, which could provide additional information on the acute effects of exercise on cognitive function. It is also crucial to increase the sample size to enhance the robustness of the findings. As for another potential avenue of research, a longitudinal study could be conducted to study the effects of HIFT and MIFT training programs on cognitive functions, stress, and anxiety. Finally, this type of intervention could be carried out on a more homogeneous sample, such as healthy university students, among other possible groups, to determine whether similar results are obtained.

4.3. Practical Applications

Regarding the practical applications of the present study, we can highlight that from a business perspective, implementing an exercise program of at least 30 min before the workday could improve concentration and reduce employee anxiety, thereby increasing productivity. This strategy would be beneficial not only for companies but also for sports centers, universities, and health professionals such as physiotherapists, allowing them to provide better service and optimize their performance in work, sports, and classes.

On the other hand, the practical application of HIIT and MIFT exercise before the workday could have significant implications for the business sector and health professionals. Its implementation would promote health and work performance, offering opportunities for interdisciplinary collaboration between physical and mental health professionals. Government agencies and occupational health organizations could also use this intervention to enhance workplace well-being, boosting productivity and reducing costs associated with absenteeism and low work productivity.

5. Conclusions

The results of the present study show that both acute single-bout training HIFT and MIFT sessions positively effects various cognitive aspects. Both HIFT and MIFT training improved the mean time per question, the fastest correct responses, and the mean time per correct response in regards to executive function, as well as concentration in the attention test. Participants in the HIFT group achieved significantly better results in regards to the number of correct responses and attention compared to the MIFT group. Regarding state anxiety, participants in the MIFT group showed significant results compared to the HIFT group, which did not exhibit changes. After stating the main findings of the study, we can affirm that we have fulfilled the objective set. Finally, the present study opens a new avenue for the scientific community to compare the effects of HIFT and MIFT on cognitive functions, stress, and anxiety in young adults.