Not All Forms of Exercise Lead to Positive Affect: A Comparative Monitoring Between an Imposed and Self-Adjusted Prescription in Recreational Runners—A Cross-Sectional Randomized Controlled Study

Abstract

Objective: To evaluate the affective responses to running with imposed velocity or self-selected time trials in runners, as well as the effects on volume load (VL) and training impulse (TRIMP). Anxiety was also determined. We established the level of association between the dependent variables. Methods: Three visits were carried out. The 1st visit consisted of a maximum running effort test (VO₂Max). In the 2nd and 3rd visits, participants were divided between the time limit (T_Lim) or time trial 1000 m running at self-selected intensity (T₁₀₀₀). Participants responded to the felt arousal, feeling, and anxiety SUDS scale before, during, and after T_Lim and T₁₀₀₀. Results: T_Lim vs. T₁₀₀₀ (p < 0.001) and V_Peak × V₁₀₀₀ (p = 0.013) showed differences, but did not influence VL_TLim vs. VL₁₀₀₀ (3181.34 ± 872.22 vs. 3570.60 ± 323.3; p = 0.062). TRIMP showed no differences (p = 0.068). Arousal did not differ between the pre-exercise (p = 0.772) and post-exercise (p = 0.083) conditions but was different during (p = 0.035). There were differences between groups in the pre-exercise (p = 0.012), during (p < 0.001), and post-exercise (p < 0.001) conditions for feeling and anxiety scores. The correlation between TRIMP and affective scores showed an association with T_Lim (r = 0.46; p = 0.043). Conclusion: The self-selected exercise generated positive affective responses, but the same did not occur for the imposed T_Lim. VL and TRIMP presented equality. There was association between TRIMP and the T_Lim feeling scale. T_Lim significantly increased anxiety scores.

1. Introduction

The literature presents evidence that intensities characterized as vigorous or close to VO₂Max stand out for promoting rapid physiological adaptations in a shorter time of exposure to exercise [1,2,3,4]. Workouts popularly known as high-intensity interval training (HIIT) [1,2,3,4] have become an interesting alternative that counteracts one of the barriers related to adherence to regular training programs, in this case, the time spent in each session. Thus, these workouts reverberate an improvement in the time–efficiency relationship [5].

However, while this exercise mode appears to be efficient in the physiological aspect [6,7,8], when in exaggerated doses or when incompatible with the training status [9], it appears to provide negative affective responses [10,11], which could encourage evasion. On the other hand, the self-selection of workloads, according to the practitioner’s preference, seems to be an interesting alternative [9,12,13,14]. Since self-regulation of the magnitude of the external load is based on interoceptive and cognitive interactions, supported by previous experiences, this condition would enable an increase in self-efficacy [15] and the achievement of a positive affective valence, without the need for fixed patterns of intensities or elaborate prescriptions.

The meta-analysis produced by Oliveira, Deslandes, and Santos [16] presents the idea that self-selected exercise vs. imposed prescription have different influences on affective responses, and that the “equal intensity” condition would demonstrate better affective responses in the self-selected exercise condition, based on the premise of greater autonomy [16]. The authors also point out that intensities above the ventilatory threshold seem to induce worse responses regarding affect. Based on this understanding, the “Dual Model” Theory seems to be the foundation for understanding such responses [16]. Additionally, it is worth noting that negative affective responses seem to reverberate in anxiety symptoms [17].

Numerous studies have observed the behavior of affective responses to self-selected and imposed work intensities [8,13,18,19] in athletes [20,21], sedentary [15,22,23,24], and overweight/obese individuals [25]. However, there are no known studies that have investigated affective and anxiety responses in middle-aged people who practice recreational physical exercise, nor in the face of stimuli with a maximum time trial characteristic, i.e., an open task. In this case, adherence is not the heart of the matter but rather the understanding of the nature of the stimulus, as well as the possible deleterious psychophysiological effects, such as on anxiety levels. Furthermore, the volume load (VL) and training impulse (TRIMP) responses to a self-selected protocol are apparently unknown. Thus, we do not know, in the “let it run freely” condition, whether VL and the TRIMP performed for the self-selected protocol could be significantly attenuated compared to the imposed programming, since these would not be practitioners engaged in high performance.

Therefore, the aim of the present study was to investigate the affective responses of middle-aged recreational runners to running stimuli with imposed and self-selected velocity (time trial characteristics), as well as the effects on aerobic performance variables (VL and TRIMP). Secondarily, as a means of observing possible stressful conditions of exercise, anxiety responses were also determined. Finally, as a tertiary outcome, the level of association between VO₂Max and anxiety scores, as well as between TRIMP and the post-exercise feeling scale, was investigated. Our primary hypothesis (H₁) is based on the construct that self-selected speed stimuli will enable ideal adjustments to effort regulation, and consequently, better affective responses, in addition to equal results on aerobic performance parameters. As a secondary hypothesis (H₂), a significant reduction in anxiety levels will be observed for the self-selected intensity condition, to the detriment of the imposed prescription. Finally, as a final hypothesis (H₃), higher VO₂Max levels will represent greater variations in anxiety scores, and higher TRIMP levels will be related to the feeling scale scores.

2. Materials and Methods

2.1. Experimental Approach

This study followed the assumptions described in the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement Guideline for randomized controlled cross-sectional study designs [26]. The research was carried out throughout the period of 2022, and had a total duration of four months, following Resolution 466/2012 of the National Health Council and being approved by the institutional research ethics committee no. (#1.220.339). All participants obtained the necessary information about the study and had their questions answered. Those who met the inclusion criteria and agreed to participate in the experiment were presented with an understanding of the possible risks inherent to the exercise, and later signed the free and informed consent form (ICF).

A total of three visits were conducted with each volunteer, with a minimum and maximum interval of 48 and 72 h, respectively, carried out in a gym. The first visit consisted of a maximum progressive effort test to estimate VO₂Max, performed on a treadmill (Technogym^® Run Now 700, Cesena, Italy). In the second and third visits, participants were divided between the time limit (T_Lim) or time trial 1000 m running at self-selected intensity (T₁₀₀₀). All volunteers performed the procedures in a closed environment, with 12 treadmills available, free from influences from the rest of the gym and with a controlled temperature between 20 and 21°. The participants performed the tests on alternate days and at the same time of day (8:00 A.M. to 10:00 A.M.). Subjects were instructed to avoid any physical exercise, alcoholic or caffeinated beverages, black tea, and the ingestion of any stimulant substance that could affect the variables tested, for 24 h before the test sessions. For the two experimental visits, each volunteer responded to three scales (felt arousal scale, feeling scale, and SUDS anxiety scale) before, during, and after an open- and closed-task test (T_Lim and T₁₀₀₀). In addition, the International Physical Activity Questionnaire (IPAQ) short version was applied to confirm the level of physical activity [27]. The results section presents Flowchart 1, referring to the processes of call, exclusion, and inclusion for the study.

2.2. Sample

The selected participants had to be physically active, properly stratified by the International Physical Activity Questionnaire (IPAQ) short version [27], and familiar with regular recreational running practice. They were recruited to participate in the study through a public call via digital media, in a high-standard gym located in the west zone of Rio de Janeiro. The calls were made during the period from June 2022 to October 2022. Participants who regularly ran at least 3 times a week and freely accepted the testing conditions, fulfilling all testing requirements, were included. Volunteers with diagnosed chronic non-communicable diseases, those who used ergogenic substances, those who had osteomyoarticular injuries, or those with a history of smoking were excluded. The characteristics of the participants are described in

Table 1. Sample characteristics.

Sample Characteristics	Experimental Group (Mean ± SD)
Age (years)	43.3 ± 4.2
Body mass (kg)	68.3 ± 9.5
Stature (cm)	170.5 ± 8.3
Body mass index (kg/m2)	23.6 ± 1.3
Training experience (years)	5.4 ± 4.3

. For the sample calculation, an ANOVA for repeated measures was considered, establishing and input of effect size = 0.40, alfa α = 0.05; Power (1-β err prob) = 0.80, number of groups = 2; number of measurements= 3; corr among rep measures = 0; this designated a sample size of 19 participants (G*Power, Version 3.1.9.4).

2.3. Procedures

2.3.1. Body Morphology

The anthropometric assessment consisted of measuring body mass using a digital scale, and height was measured using a standard wall-mounted stadiometer (Sanny, Brazil).

2.3.2. Progressive Maximal Exercise Test

The subjects started by walking on the treadmill at 5.0 km·h⁻¹ at 0% slope for two minutes. From this initial stage, increments of 1.0 km·h⁻¹ (approx. 1 MET) were administered every two minutes, aiming to achieve maximum performance and effort until voluntary exhaustion. Maximum oxygen consumption was estimated according to the equation proposed by the American College of Sports Medicine (ACSM) and is shown in

Table 2. VO₂Max estimation equation.

VO2Max = (0.2 × velocity × slope) + 3.5
Where VO2Max—maximum oxygen consumption in mL·kg1·min1; Velocity—m·min−1; Slope—centesimal unit.

. Heart rate responses (Polar^® monitor model RS800, Kempele, Finland) as well as rate of perceived exertion—RPE (Borg 0–10) were monitored and recorded every minute until exhaustion. The presence of signs or symptoms mentioned by the participants, or maximum voluntary exhaustion itself, was used as a criterion for completing the test.

2.3.3. Time to Exhaustion Protocol (T_Lim)

A 5 min warm-up was performed at a self-selected intensity. Participants underwent a T_Lim test on a treadmill without an incline being imposed. After 5 min, participants moved off the treadmill, where for a period of one minute the treadmill was adjusted to peak velocity (V_Peak). Participants were continuously encouraged to sustain the intensity for as long as possible. The test aimed to determine the maximum achievable duration at the intensity associated with VO₂Max (100%) or V_Peak. The values collected in minutes were converted to seconds for later analysis. RPE was monitored at 60 s intervals and then 15 min after the end of the session (session RPE).

2.3.4. 1000 m Time Trial Protocol (T₁₀₀₀)

After a 5 min warm-up at a self-selected intensity, participants took a 1 min rest. During the rest, the intensity was adjusted to 8 km·h⁻¹, and then the participants stood on the treadmill. After getting on, participants were free to increase or decrease their working velocity in order to complete the 1000 m as quickly as possible. RPE was monitored at 60 s intervals and then 15 min after the end of the session (session RPE).

2.3.5. Subjective Measurement Instruments

Body arousal and feeling scales were applied at three times: pre-exercise, during (between 2 and 2 min 30 s), and 5 min after exercise. The SUDS anxiety scale was applied before and 5 min after the exercise sessions. The perceived exertion (RPE Borg 0–10) was applied after 15 min of the exercise session.

Felt arousal scale: the level of body arousal was analyzed in a self-perceived way during the experimental conditions: pre- and post-physical exercise performed. It comprised a Likert scale, which varied linearly from 1 = slightly activated, to 6 = very activated, with intermediate values.

Feeling scale: the dimensions of affective responses were determined by the level of positive, neutral, or bad sensation provided by the aerobic exercise, being distributed on a bipolar ordinal scale, ranging from zero (0) as a neutral position; +1 = reasonably good to +5 = very good; −1 = reasonably bad, up to −5 = very bad.

Rating of perceived exertion (RPE): the adapted linear RPE scale (0 to 10) as produced and described by Borg was used, where “0” refers to the perception of ‘extremely light’ effort, reaching “total fatigue” at 10. For the self-selected sessions, participants were induced and motivated to obtain the maximum global effort index.

SUDS anxiety scale: each participant described how they felt at that moment according to their perceived mental state, scoring on a linear scale between 0—absolutely no anxiety, and 10—extremely anxious.

2.3.6. Calculation of Volume Load and Training Impulse (TRIMP)

The volume load (VL) was calculated based on the product of the total work achieved for T_Lim or T₁₀₀₀ performed in both tests by the average velocity. To calculate the TRIMP, as suggested by Banister and adapted by Foster, the VL measurement was used, multiplied by the RPE of the session [28,29].

2.3.7. Randomization Process

Participants, after eligibility and written informed consent, were randomly assigned to experimental assessments of T_Lim and T₁₀₀₀ time trials. The randomization sequence was computer generated (www.randomizer.org, accessed on August 2022) and allocated by a third member of the research group, kept blind until the time of the experiment.

2.3.8. Data Analysis and Processing

To avoid possible biases in the analysis, the data were collected by a researcher associated with the project and the research group (P.A and E.P.) and analyzed by a third researcher (group leader A.S). The researcher responsible for data analysis remained blind throughout the data collection process. The names of all participants remained confidential, being excluded from the technical file and replaced by numbers.

2.3.9. Statistical Analysis

A descriptive analysis of the data was performed and presented as mean ± standard deviation (SD), 95% confidence interval (CI95%), median, and maximum and minimum values. Data normality was tested using the Shapiro–Wilk test. If normality was present (p > 0.05), data were expressed as mean ± standard deviation. If normality was violated (p < 0.05), data were expressed as median and maximum and minimum values. Given that the aerobic performance variables (T_Lim, T₁₀₀₀, V_Peak, V₁₀₀₀) presented normality, the Student’s t-test for paired samples was used. In addition, a Wilcoxon test was used to compare the scores of the arousal, feeling, and anxiety scales. As pairwise comparisons, that is, to investigate the effect of time, the Friedman test was performed. A correlation test was applied between the VO₂Max variable with differences in anxiety level scores, as well as TRIMP and feeling scores. Delta % (Δ%) was also calculated for the anxiety score variables. All analyses were carried out using SPSS software (Version 27.0 for Windows^®; Chicago, IL, USA), with a statistical significance of p ≤ 0.05 adopted.

3. Results

Figure 1 presents the entry, inclusion, and exclusion criteria for the sample participants. After Shapiro–Wilk distribution analysis, normality was observed for the variables VO₂Max (p = 0.170), V_Peak (p = 0.167), T_Lim (p = 0.242), T₁₀₀₀ (p = 0.072), V₁₀₀₀ (p = 0.200), and VL (p = 0.359). However, the same was not observed for perception of exertion (RPE: p < 0.001), which was therefore treated in a non-parametric manner. The general results regarding the conditioning of the participants in this study are presented in

Table 3. Aerobic performance responses to the imposed T_Lim and self-selected T₁₀₀₀ experimental protocol.

		Imposed			Self-Selected
	VO2Max	TLim	VPeak		T1000	V1000
	(mL·kg−1·min−1)	(s)	(km·h−1)	(%)	(s)	(km·h−1)	(%)
Mean	51.1	220.7	14.3	100.0	284.8	12.9	90.0
SD	5.7	43.8	1.7	0.0	35.1	1.7	6.4

T_Lim = time limit until exhaustion; V_Peak = peak velocity; T₁₀₀₀ = time taken to cover 1000 m. V₁₀₀₀ = average velocity for 1000 m; SD = standard deviation.

.

3.1. Primary Outcomes

Significant differences were observed between T_Lim and T₁₀₀₀ (p < 0.001) and V_Peak and V₁₀₀₀ (p = 0.013). However, there were no significant differences regarding VL_TLim and VL₁₀₀₀ (3181.34 ± 872.22 vs. 3570.60 ± 323.3; p = 0.062), suggesting equality in the work performed. Likewise, RPE_TLim and RPE₁₀₀₀ (median = 10.0; CI95% = 9.8–10.0 vs. median = 10.0; CI95% = 9.3–9.9, respectively, for T_Lim and T₁₀₀₀) were analyzed through the non-parametric Mann–Whitney test, in which no significant difference was observed (Mann–Whitney U = 141.50; p = 0.072). Similarly, for the TRIMP between the T_Lim and T₁₀₀₀ sessions, no significant difference was evidenced (Mann–Whitney U = 118.000; p = 0.068). Figure 2 shows the comparison of the TRIMP between experimental protocols.

Regarding the comparison between the types of treatment (T_Lim vs. T₁₀₀₀) for the felt arousal scale pre-exercise (Z = −0.284; p = 0.776), during (Z = −2.111; p = 0.035), and post-exercise (Z = −1.732; p = 0.083), differences were observed only during the experimental procedures. The Friedman test was used for comparison of the time factors, with a significant difference being observed for both T_Lim and T₁₀₀₀ (p = 0.001; p = 0.001, respectively), both increasing significantly after intervention. Figure 3 shows the differences between groups and moments for the activation scale.

For the feeling scale, the Wilcoxon test showed significant differences between groups for the pre-exercise (Z = −2.501; p = 0.012), during (Z = −3.739; p < 0.001), and post-exercise (Z = −3.532; p < 0.001) conditions. The Friedman test was used to compare the time factor in the feeling scale, showing differences for both interventions (p = 0.015; p < 0.001, respectively, for T_Lim and T₁₀₀₀). For the T_Lim intervention, there was a significant reduction, while for T₁₀₀₀, there was a significant increase in affective valence. Figure 4 shows the differences between groups and moments for the feeling scale.

3.2. Secondary Outcome

After determining the differences between the pre and post conditions for anxiety scores, the Wilcoxon analysis showed no differences between groups between the pre conditions (Z = −1.515; p = 0.130); however, it demonstrated differences between groups for the post conditions (Z = −3.485; p < 0.001). For the time factor, differences were observed for T_Lim (Z = −2750; p = 0.006) and T₁₀₀₀ (Z = −3.501; p < 0.001).

Table 4. Pre- and post-exercise anxiety scores in the face of T_Lim intervention and T₁₀₀₀ time trial.

	TLim				T1000
	Pre (Score)	Post (Score)	Diff (Absolute)	∆ (%)	Pre (Score)	Post (Score)	Diff (Absolute)	∆ (%)
Mean	3.9	4.8	0.9	23	4.3	2.7	1.6	−37
SD	0.9	1.3			1.6	1.4

T_Lim = time limit until exhaustion; T₁₀₀₀ = time taken to cover 1000 m. ∆% = percentage variation from pre- and post-exercise moments for the anxiety scale. Diff = differences between pre- and post-exercise conditions.

presents the pre- and post-intervention anxiety response values. Figure 5 presents the individual anxiety responses for both experimental protocols.

3.3. Tertiary Outcome

Spearman’s correlation showed no association between VO₂Max values and the percentage variation in anxiety scores (r = 0.125; p = 0.610; r = 0.122; p = 0.631), suggesting that anxiety variations were independent of a low or high level of VO₂Max. However, Pearson’s correlation (normality observed only for TRIMP derived from T_Lim) between the TRIMP performance measure and the final scores of the affective scale showed a significant and positive association for the T_Lim experiment (r = 0.46; p = 0.043), suggesting that the greater the training impact achieved, the better the affective scores. The correlation between TRIMP and the sensation scale for the self-selected experiment was not significant (p = 0.190). Figure 6 shows the correlation performed. The affective domains are presented graphically based on the circumplex model represented in Figure 7. The circumplex model was structured in two dimensions using the feeling and felt arousal scales, represented in a Cartesian parameter.

3.4. Unintended Harm

Risks to health and physical integrity are inherent to physical exercise. Therefore, we monitored the effects of exercise sessions and the potential risks and harmful effects resulting from the exercise administered. For this purpose, in our study, no negative severe events resulting from the imposition of high-intensity load were observed. The sample showed potential adaptation regarding work in critical efforts. However, it is worth noting that the imposed exercise (T_Lim) induced significant discomfort and nausea during its practice, mainly in participants with lower capacity and tolerance. Since this format of running performance is not routine, the appearance of discomfort at a high intensity is possible. Adequate guidance was provided to the participants and contact was maintained until the appropriate period.

4. Discussion

The aim of this study was to evaluate the affective responses of middle-aged recreational runners to running stimuli with an imposed or self-selected velocity in a time trial format. Secondarily, as a means of observing possible stressful conditions of exercise, anxiety responses were also determined during the session with imposed or self-selected loads. Finally, relationships between VO₂Max and anxiety, as well as TRIMP and sensation responses, were also established.

Firstly, our hypothesis H₁ proved to be true, since the 1000 m time trial stimulus produced positive effects on affect. In principle, to our knowledge, this is the first study to investigate the nature of time trial stimulus. For the most part, when the self-selection of intensity system is proposed, the literature establishes continuous patterns of intensity maintenance [30] or RPE fixed at a certain score [8]. Our findings establish that self-selected stimuli, even at their maximum demand, are an interesting form of aerobic exercise prescription, contributing to the optimization of training time (time-efficient strategy) and a faster development of cardiorespiratory skills.

In contrast, when we exposed participants to rectangular stimuli at constant load in the severe domain of exercise (100% of the velocity associated with VO₂Max), the physiological stress became exacerbated and constant for several minutes, quickly leading to exhaustion. The T_Lim observed in our study differed in its magnitude when compared to trained subjects (220.7 ± 43.8 vs. 404.0 ± 101 s), respectively, for our study and in the study of Billat et al. [31], suggesting that participants, despite being regular in their running schedule, are far from a status classified as trained (i.e., the largest portion of the population that regularly practices exercise). Thus, our results seem to support the idea that the nature of this type of stimulus (under severe domain), even in the presence of participants engaged and experienced in the recreational activity of running, is not sustainable as a means of prescribing training.

The negative outcomes of affect observed in T_Lim (Pre: 1.16 ± 0.9 vs. Post: −1.32 ± 3.7), compared to self-selected intensity, can be explained based on the dual model theory, where cognitive and interoceptive factors define behavior. According to Acevedo and Ekkekakis [14,25,32], in this exercise domain, the disruption of homeostasis is severe, therefore, it suffers a strong influence from peripheral metabolic signaling. However, both experimental conditions passed through the severe exercise domain (T_Lim: 100% vs. T₁₀₀₀: 90%) and obtained different responses. In this particular case, we believe that cognitive factors predominated to the detriment of interoceptive mechanisms, reflecting inexperience with the nature of T_Lim. It appears that under these conditions, there is a significant decrease in prefrontal activity combined with increased activation of the amygdala, resulting in a type of emotional coping, which would explain the decline seen in affective valence [33].

When comparing the aerobic performance variables, we can observe that both experimental models presented significant differences (T_Lim vs. T₁₀₀₀—p < 0.001; V_Peak × V₁₀₀₀—p = 0.013). However, it is important to highlight that both T_Lim and T₁₀₀₀ passed through the same exercise domain, which confers, according to Hill, Poole, and Smith [34], similar physiological instability effects between the tasks, and similar adaptive potentials [35], only differing in the time taken to reach VO₂Max and exhaustion [33,34]. It is worth highlighting that such divergence was presented with a compensation mechanism between the variables (time and velocity), which is reflected in the equality in the results of VL and TRIMP, which did not differ between the experimental tasks.

TRIMP has been used to characterize exercise load during competitive time trial tasks and has been useful for controlling training load in long-term planning [28,29]. However, to date, it has not been used to observe possible associations with affective responses or the impact between training models. First, our study demonstrates that the self-selected protocol did not underestimate the impact of exercise, validating our initial hypothesis. The prescription in the maximum time trial model; therefore, can be designed and incorporated into training programs for adults already engaged in regular training programs. In addition, there was a significant and positive association between TRIMP and post-exercise sensation scores for the imposed T_Lim exercise model, suggesting that the greater the external load (100%) and the time achieved, the better the affective responses. This can be explained by the variability between participants and the heterogeneity of performances, demonstrating that those who were most potentially adapted modulated the feelings of fatigue and exhaustion, even when faced with a high imposed load, in a differentiated way in comparison to those with a lower training status.

Verame et al. [36] presented positive and similar psychoaffective responses to two protocol models and to high intensity (ratio 1:2: RPE 17 vs. 1:0.5: RPE 16) in trained participants, which suggests that trained participants showed a better modulation of positive responses, regardless of the stimulus configuration [36]. However, Rose and Parfitt [15] point out significant variability in affective responses to imposed (above the ventilatory threshold) and self-selected workloads, such that sedentary participants transitioned positively to intensities above the ventilatory threshold, with no differences to the group of active women. Logically, the domain in which the exercise was performed was different from that suggested in our study (heavy vs. severe), which would explain the differences in our outcomes.

Finally, the circumplex model shows us that despite the high physiological demands of the self-selected time trial exercise model, such activation and feeling responses largely moved throughout the upper right quadrant of the Cartesian plane during the exercise, suggesting that the self-adjustment of intensities throughout the exercise reflected high levels of excitement and reward upon its completion. Differently, the circumplex model for T_Lim moved under the upper left quadrant of tension, which would explain the results related to anxiety. We know that an exacerbation of the anxiety response is appropriate in the face of threatening conditions and reverberates as physiological changes; however, to a certain extent, it also negatively affects performance results [37]. Although we did not observe a significant association between VO₂Max levels and anxiety scores in our study, refuting our hypothesis, we believe that such outcomes interfered with the participants individually in the T_Lim protocol, especially with regard to participants with a lower training status, who generally have a lower tolerance to high levels of effort and the ability to deal with threatening conditions.

In general terms, physical exercise is related to a reduction in anxiety levels in healthy people and in patients diagnosed with generalized anxiety disorders [38], panic [39], and depressives. This appears to occur at moderate intensities and even during maximum effort tests [40]. Despite this understanding, no study has specifically measured the potential effects of a T_Lim protocol on anxiety levels, which makes comparisons difficult. In our study, we observed a 23% increase in anxiety scores after T_Lim, which potentially had a negative impact on performance. Furthermore, it is clear to us, as shown in Figure 4, that participants exhibited significant variability in response to this stimulus model, which further suggests a dependence on intrinsic physiological factors not measured in our study.

In practical terms, if coaches, physiologists, and runners wish to promote an increase in affective responses, even in maximum exercise sessions, we suggest the application of open-ended tasks (T₁₀₀₀), since, in addition to appearing to be associated with improvements in performance metrics, they appear to be associated with positive affective responses. This is unique knowledge and can be applied to runners and eventually to programs whose objective is to improve the emotional well-being of those involved. It is worth noting that the findings of the present study should be limited to the population that comprised our sample, which comprised adult and middle-aged recreational runners. Notably, apparently, it is this population that is commonly engaged in middle- and long-distance running [41].

The cross-sectional research design of the present study can be characterized as a limitation. The main characteristic of cross-sectional studies is that they obtain measurements at a single point in time. Therefore, there was no follow-up period for the individuals, which does not allow us to know what would happen to the variables investigated after a training period, and we could not establish a suitable cause and effect relationship [42]. Therefore, the results of the present study cannot be interpreted in a causal sense. Furthermore, we suggest that future investigations perform the same measures chronically, in an attempt to track these variables over a follow-up period.

5. Conclusions

In our primary outcome, the self-selected time trial exercise protocol was able to generate significant and positive affective responses, even when faced with an imposition of maximal effort. The same did not occur for the imposed T_Lim. The different results of the aerobic performance variables did not impact the VL and TRIMP, which were equal. However, the positive association between TRIMP and the scale of sensation in relation to T_Lim suggests that participants with greater performance potential tend to manifest positive affective responses. Finally, the T_Lim protocol generated a significantly stressful environment, resulting in higher post-exercise anxiety scores, and was also not associated with VO₂Max levels.