1. Introduction
The literature presents evidence that intensities characterized as vigorous or close to VO
2Max stand out for promoting rapid physiological adaptations and 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, reverberating in an improvement in the time/efficiency relationship [
5].
However, at the same time as this exercise mode appears to be efficient on the physiological aspect [
6,
7,
8], in exaggerated doses or incompatible with the training status [
9], appear to provide negative affective responses [
10,
11], which could encourage evasion. On the other hand, 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, such a 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 influence affective responses differently, and 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, as well as 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 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 whether, in the “let it run freely” condition, VL and the TRIMP impulse performed for the self-selected protocol could be significantly attenuated compared to the imposed programming, since these are practitioners not engaged in high performance.
Therefore, the aim of the present study was to investigate the affective responses to running stimuli with imposed and self-selected velocity (time trial characteristics) by middle-aged recreational runners, 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 of effort regulation, 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.
Procedures
Body Morphology
The anthropometric assessment consisted of measuring body mass using an digital scale and height measured using a standard wall-mounted stadiometer (Sanny, Brazil).
Progressive Maximal Exercise Test
The subjects started 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 at achieving 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 shown in Board 1. Heart rate responses (Polar® monitor model RS800), as well as 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.
Board 1. VO2Max estimation equation. |
VO2Max = (0,2 x velocity x slope) + 3,5 |
Where: VO2Max - maximum oxygen consumption in mL·kg1·min1; Velocity – m·min-1 Slope – centesimal unit |
Time to Exhaustion Protocol (TLim)
A 5-minute warm-up was performed in a self-selected intensity. Participants underwent a TLim test on a treadmill without imposing an incline. After 5 min, participants moved off the treadmill, where for a period of one minute the treadmill was adjusted to peak of velocity (VPeak). 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 VPeak. The values collected in minutes were converted to seconds for later analysis. RPE was monitored at 60-s intervals and 15 min after the end of the session (session RPE).
1000m Time Trial Protocol (T1000)
After a 5-min warm-up at self-selected intensity, participants took a one-minute rest. During the rest, the intensity was adjusted to 8 km·h-1, and then, participants entered the treadmill. After entering, participants were free to increase or decrease their working velocity in order to complete the 1000m as quickly as possible. RPE was monitored at 60-s intervals and 15 min after the end of the session (session RPE).
Subjective Measurement Instruments
Body arousal and feeling scales were applied at three times: pre-exercise, during (between 2 and 2 min 30 sec) and 5 min after exercise. The SUDS anxiety scale was applied before and 5 min after 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 is a Likert scale, which varies linearly from 1 = slightly activated, to 6 = very activated, with intermediate values.
Feeling scale: the dimensions of affective responses are determined by the level of positive, neutral, or bad sensation provided by 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” 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 he or she feels at the moment according to his or her perceived mental state, scoring on a linear scale between: 0- absolutely no anxiety; and 10- extremely anxious.
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 T
1000 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 [
27,
28].
Randomization Process
Participants, after eligibility and written informed consent, were randomly assigned to experimental assessments of T
Lim and T
1000 time trial. The randomization sequence was computer generated (
www.randomizer.org) and allocated by a third member of the research group, keeping it blind until the time of the experiment.
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.
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 (TLim, T1000, VPeak, 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 associated 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 performed using SPSS 20.0 for Windows® software (Chicago, USA), with a statistical significance of p ≤ 0.05 adopted.
4. Discussion
The aim of this study was to evaluate affective responses to running stimuli with imposed or self-selected velocity in a time trial format by middle-aged recreational runners. 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 H
1 proved to be true, since the 1000m time trial stimulus produced positive effects on affect. In principle, to our knowledge, this is the first study that investigated the nature of the time trial stimulus. For the most part, when the self-selection of intensity system is proposed, the literature establishes continuous patterns of intensity maintenance [
29] 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 expose participants to rectangular stimuli at constant load, in the severe domain of exercise (100% of the velocity associated with VO
2Max), the physiological stress becomes 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 sec, respectively for our study and the study of Billat et al. [
30], 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 & Ekkekakis [
14,
25], in this exercise domain, the disruption of homeostasis is severe, therefore, suffering a strong influence from peripheral metabolic signaling. However, both experimental conditions passed through the severe exercise domain (T
Lim: 100% vs. T
1000: 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 [
31].
When comparing the aerobic performance variables, we can observe that both experimental models presented significant differences (T
Lim vs. T
1000 - p < 0.001; V
Peak x V
1000 - p = 0.013). However, it is important to highlight that both T
Lim and T
1000 passed through the same exercise domain, which confers, according to Hill, Poole & Smith [
32], similar physiological instability effects between the tasks, and similar adaptive potentials [
32], only differing in the time taken to reach VO
2Max and exhaustion [
33,
34]. It is worth highlighting that such divergence was presented with a compensation mechanism between the variables (time and velocity), which was reflected in equality in the results of VL and TRIMP, not differing 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 [
27,
28]. However, to date, it has not been used to attempt 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 heterogeneity of performances, demonstrating that those who were most potentially adapted modulated the feeling, fatigue and exhaustion, even when faced with a high imposed load, in a differentiated way, when compared to those with a lower training status.
Verame et al. [
35] present positive and similar psychoaffective responses to two protocol models and high intensity (ratio 1:2: RPE 17 vs. 1:0.5: RPE 16) in trained participants, which suggests facilitation on the part of trained participants in modulating positive responses, regardless of the stimulus configuration [
35]. However, Rose & Parfitt [
15] point out significant variability in affective responses to imposed (above the ventilatory threshold) and self-selected workload, such that sedentary participants transitioned positively to intensity above the ventilatory threshold, with no differences for the group of active women. Logically, the domain in which the exercise was performed is 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 in the self-selected time trial exercise model, such activation and feeling responses largely moved throughout the exercise in the upper right quadrant of the Cartesian plane, suggesting that the self-adjustment of intensities throughout the exercise reflected high levels of excitement and reward at 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 in physiological changes, however, to a certain extent, it also negatively affects the performance result [
36]. Although we did not observe a significant association between VO
2Max levels and anxiety scores in our study, refuting our hypothesis, we believe that such outcomes interfered individually with the participants in the T
Lim protocol, especially with regard to participants with lower training status, who generally have lower tolerance to high levels of effort and the ability to deal with threatening conditions.
In general terms, physical exercise is related to the reduction of anxiety levels in healthy people and in patients diagnosed with generalized anxiety disorders [
37], panic [
38] and depressives. This appears to occur at moderate intensities and even during maximum effort tests [
39]. 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 observed in
Figure 4, that participants exhibited significant variability in response to this stimulus model, which further suggests the dependence on intrinsic physiological factors not measured in our study.