Severe hypoxia during incremental exercise to ...

Physiology & Behavior 156 (2016) 171–176

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Severe hypoxia during incremental exercise to exhaustion provokes negative post-exercise affects Michail E. Keramidas a,b,⁎, Nektarios A.M. Stavrou c,d, Stylianos N. Kounalakis b, Ola Eiken a, Igor B. Mekjavic b a

Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Stockholm, Sweden Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Ljubljana, Slovenia Exercise and Sport Science Department, ASPETAR Orthopaedic and Sports Medicine Hospital, Doha, Qatar d Faculty of Physical Education and Sport Science, University of Athens, Athens, Greece b c

H I G H L I G H T S • Maximal whole-body exercise in hypoxia provokes negative post-exercise emotions. • The emotional reactions were independent of the maximal exercise intensity. • Hypoxia per se might be the key component mediating the post-exercise affects.

a r t i c l e

i n f o

Article history: Received 20 March 2015 Received in revised form 9 November 2015 Accepted 19 January 2016 Available online 21 January 2016 Keywords: Effort Emotion Fatigue Mood Performance _ 2peak VO

a b s t r a c t The post-exercise emotional response is mainly dependent on the intensity of the exercise performed; moderate exercise causes positive feelings, whereas maximal exercise may prompt negative affects. Acute hypoxia impairs _ 2peak ), resulting in a shift to a lower absolute intensity at the point of exhaustion. Hence, the peak O2 uptake (VO purpose of the study was to examine whether a severe hypoxic stimulus would influence the post-exercise affective state in healthy lowlanders performing an incremental exercise to exhaustion. Thirty-six male lowlanders performed, in a counter-balanced order and separated by a 48-h interval, two incremental exercise trials to ex_ 2peak , while they were breathing either room air (AIR; FiO2: 0.21), or a hypoxic haustion to determine their VO gas mixture (HYPO; FiO2: 0.12). Before and immediately after each trial, subjects were requested to complete two questionnaires, based on how they felt at that particular moment: (i) the Profile of Mood States-Short Form, and (ii) the Activation Deactivation Adjective Check List. During the post-exercise phase, they also com_ 2peak was significantly lower in the HYPO than the AIR trial pleted the Multidimensional Fatigue Inventory. VO (~15%; p b 0.001). Still, after the HYPO trial, energy, calmness and motivation were markedly impaired, whereas tension, confusion, and perception of physical and general fatigue were exaggerated (p ≤ 0.05). Accordingly, present findings suggest that an incremental exercise to exhaustion performed in severe hypoxia provokes negative post-exercise emotions, induces higher levels of perceived fatigue and decreases motivation; the affective _ 2peak than that achieved in normoxic conditions. responses coincide with the comparatively lower VO © 2016 Elsevier Inc. All rights reserved.

1. Introduction A single bout of dynamic exercise influences the affective responses of healthy individuals through central and local cues, typically by alleviating the negative mood and enhancing the positive mood state [1–4]. Yet, the nature of the post-exercise emotional response is, to a large extent, dose-dependent, with the exercise intensity suggested as the most ⁎ Corresponding author at: Department of Environmental Physiology, Swedish Aerospace Physiology Center, School of Technology and Health, Royal Institute of Technology, Berzelius väg 13, SE-171 65 Solna, Sweden. E-mail address: [email protected] (M.E. Keramidas).

http://dx.doi.org/10.1016/j.physbeh.2016.01.021 0031-9384/© 2016 Elsevier Inc. All rights reserved.

critical determinant [5]. A number of studies have shown that exercise at low-to-moderate intensity prompts positive feelings, whereas maximal exercise to exhaustion is mainly associated with unpleasant affects, such as an increase in distress and perceived fatigue, and decrease in vigor [5–7]. Acute hypoxia precipitates a reduction in maximal exercise tolerance, thereby resulting in a shift to a lower absolute intensity at the point of exhaustion, as the lower peak values of heart rate (HR), cardiac output and blood lactate concentration indicate [8–11]. Judging by ratings of perceived exertion [12] at the peak work-rate of an incremental exercise to exhaustion, no differences exist between normoxia and hypoxia as regards both the local-muscular and the central-overall

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M.E. Keramidas et al. / Physiology & Behavior 156 (2016) 171–176

sensation of effort [13]. Still, it remains unknown whether the postexercise affective responses would also be similar following an incremental exercise to exhaustion in hypoxia, despite the lower absolute work intensity than in normoxia. Accordingly, the purpose of the present study was to examine the effects of an incremental exercise to exhaustion performed under severe normobaric hypoxia on the post-exercise affective state in a cohort of physically active, male lowlanders. Considering that the integration of emotional and cognitive operations occurs mainly in the prefrontal cortex [14], a brain area that is directly affected by severe hypoxia during maximal exercise [15–22], we hypothesized that acute hypoxia would evoke unpleasant post-exercise affects, regardless of the impaired exercise performance and the consequent lower absolute intensity. 2. Materials and methods 2.1. Participants Thirty-six healthy males participated in the study (age: 22.6 ± 3.5 years; body mass: 74.0 ± 6.3 kg; stature: 179.9 ± 5.7 cm; body fat: 10.8 ± 3.3%). All subjects were aerobically fit, and had no history of any cardiovascular, pulmonary or mental disease. They were nearsea level residents, and had not been exposed to altitude N 500 m for at least a month preceding the experiments. The subjects were informed in detail about the experimental procedures, and gave their written consent. They were instructed not to engage in any strenuous physical activity and to refrain from consuming alcohol or any caffeinated product a day before the tests. The experimental protocol was approved by the National Committee for Medical Ethics at the Ministry of Health of the Republic of Slovenia and conformed to the Declaration of Helsinki. 2.2. Experimental protocol The study was conducted at the Orthopedic Hospital Valdoltra (Ankaran, Slovenia). On a first visit to the laboratory, subjects were thoroughly familiarized with the equipment and experimental procedure. Thereafter, they performed two incremental exercise trials to exhaustion on an electrically braked cycle ergometer (ERG 900S, Schiller, Baar, Switzerland). During the trials, they were breathing either room air [AIR; fraction of inspired O2 (FiO2): 0.21], or a hypoxic gas mixture (HYPO; FiO2: 0.12; corresponding to a simulated altitude of ~4500 m). The trials were conducted in a counter-balanced order, at the same time of the day (morning hours) and interspersed by a 48-h interval to avoid any residual effect from the previous exercise trial. The mean temperature, relative humidity and barometric pressure in the laboratory were 22.2 ± 0.6 °C, 54 ± 6% and 754 ± 5 mm Hg, respectively. Both trials commenced with a 10-min resting period on the cycle ergometer to record baseline values. In the HYPO trial, the 10-min rest comprised of 5 min breathing room air, followed by 5 min breathing hypoxic gas. Thereafter, subjects were asked to complete a 2-min warm-up at a work rate of 60 W. Subsequently, the load was increased by 30 W·min−1 until exhaustion. The subjects selected their preferred pedaling cadence (between 60 and 70 rpm). Attainment of the peak ox_ 2peak ), defined as the highest VO _ 2 averaged over 60 s, ygen uptake (VO was confirmed according to the following criteria, listed in priority order: (i) severe fatigue or exhaustion resulting in an inability to maintain exercise at a given work rate (cycling cadence b 60 rpm), (ii) a pla_ 2 , and/or (iii) a subjective rating of perception of effort at or teau in VO near maximal. Throughout each trial, subjects remained seated on the cycle ergometer, and received verbal encouragement always in the same manner and by the same investigator. Before and immediately after each trial, subjects were requested to complete three questionnaires (see below for details).

2.3. Instrumentation 2.3.1. Respiratory measurements _ _ 2 , ventilation (VE), respiratory frequency (fR), tidal volume (VT) VO

and partial pressure of end-tidal carbon dioxide (PETCO2) were measured on-line with a metabolic analyzer (CS-200, Schiller, Baar, Switzerland). The gas analyzer and the pneumotachograph were calibrated before each trial with two different gas mixtures and a 3-L syringe, respectively. During the HYPO trial, subjects breathed through a low-resistance two-way respiratory valve (Model 2700 T-Shape; Hans Rudolph, Shawnee, OK, USA). The inspiratory side of the respiratory valve was connected via a respiratory corrugated tubing to a 200-L Douglas bag, which was continuously filled with the pre-mixed humidified breathing mixture.

2.3.2. Heart rate (HR) and peak power output (PPO) HR was measured and recorded using a heart rate monitor (S800CX, Polar, Kempele, Finland). PPO was calculated from the last completed workload by adding the fraction of the time spent at the final noncompleted workload multiplied by 30 W. 2.3.3. Capillary oxyhemoglobin saturation (SpO2) SpO2 was monitored with a finger pulse oximeter (BCI 3301, Waukesha, WI, USA) on the left index finger. 2.3.4. Psychological measurements Five minutes before and 5 min after each trial, subjects were requested to fill out the following questionnaires, based on how they felt at that particular moment: (i) the Profile of Mood States-Short Form (POMS-SF; [23]), and (ii) the Activation Deactivation Adjective Check List (AD ACL; [24]). During the post-exercise phase, they also completed the Multidimensional Fatigue Inventory (MFI; [25]). All the questionnaires were presented in a hardcopy format, and they were explained to the subjects by the same investigator prior to each trial. Subjects replied to the questions in 4-to-8 min, while seated comfortably in a chair and breathing room air. The POMS-SF is a 37-item self-evaluation questionnaire of six subscales: tension-anxiety, depression-dejection, anger-hostility, vigoractivity, fatigue-inertia and confusion-bewilderment. The description of the subjects' feelings was provided based on a 5-point scale with anchors from 0-“not at all” to 4-“extremely”. The validity and reliability of the instrument has been reported previously [23]. The AD ACL is a self-report instrument that consists of 20 items, and provides measures of energy, tiredness, tension, and calmness. Each item is answered by a four-point rating scale, which is scored from 1“definitely do not feel” to 4-“definitely feel”. The total score of each factor was calculated by adding each items' score ranged from 5 to 20. The MFI is a 20-item self-rating multidimensional inventory measuring different aspects of fatigue: general fatigue, physical fatigue, reduced activity, reduced motivation, and mental fatigue. Each subscale contains four items and the answer ranges from 1-“yes, that is true” to 5-“no, that is not true”; the higher the value in each subscale (ranges from 4 to 20) the higher the subjects' fatigue. The validity and the reliability of the MFI are well documented [25]. 2.4. Statistical analyses Statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) 21.0 (IBM Corporation, NY, USA). All data are reported as mean (SD), unless otherwise indicated. Data pre-screening was conducted, including univariate and multivariate distribution analyses. Skewness and kurtosis indicated acceptable values in the examined variables. A 2 (trials; NOR vs. HYPO) × 2 (testing time; pre vs. post) multivariate analysis of variance (MANOVA) with repeated measures on the second factor was conducted to examine the differences


in POMS-SF and AD ACL subscales. When MANOVAs revealed significant F-ratio for interactions and/or main effects, separate repeated analyses of variance (ANOVA) were performed on each subscale of the POMSSF and AD ACL. A one-way (trials; NOR vs. HYPO) MANOVA analysis was performed for the MFI factors. When the assumption of sphericity was violated, the degrees of freedom were adjusted using the Greenhouse-Geisser correction. Bonferroni corrected t-tests followed any significance between and within effects in the ANOVA models testing pairwise comparisons. The internal consistency of the POMS-SF, AD ACL and MFI subscales was examined with Cronbach's a coefficient. Cronbach's a values ranged for the POMS-SF subscales from 0.74 to 0.88, for the AD ACL from 0.64 to 0.83, and for the MFI subscales from 0.56 to 0.87, indicating an acceptable subscale reliability. A paired sample Student's t-test was used to detect significant changes between the maximum cardiorespiratory values in the two trials. Pearson's product moment correlation (r) was utilized to assess the relation between selected physiological and psychological variables. Magnitudes of correlations were interpreted qualitatively using Cohen's scale: r b 0.1: trivial, 0.1–0.3: small, 0.3–0.5: moderate, N0.5: large. The alpha level of significance was set a priori at 0.05.

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trial (p = 0.001), but did not change overtime in any of the experimental conditions (p = 0.49). After both exercise trials, a markedly higher degree of perceived fatigue was reported (p b 0.001), with no interconditional difference (p = 0.23). No differences were observed for anger and depression either between conditions or overtime (p N 0.05). 3.2.2. AD ACL The mean values of AD ACL subscales are summarized in Table 3. The exercise trial (2) × testing time (2) repeated measures MANONA on the AD ACL showed an interaction (p b 0.01, η2p = 0.197), and a main effect of time (p b 0.001, η2p = 0.504). The tiredness was increased after both trials (p b 0.001), but it was profounder in the HYPO trial (p = 0.01). Subjects were tensed after the HYPO trial (p b 0.001), but not after the AIR trial; a statistical tendency (p = 0.08) for a greater tension after the HYPO than the AIR trial was also observed. After the HYPO trial, subjects were less calm than before the HYPO trial (p b 0.001) and than after the AIR trial (p = 0.006). The perceived energy did not alter after any of the trials (p = 0.56). However, although no inter-condition difference was observed at the pre-exercise phase (p = 0.23), subjects felt less energetic after the HYPO trial than after the AIR trial (p = 0.03).

3. Results

higher in the HYPO than the AIR trial (p ≤ 0.05); VT did not differ between the trials (p = 0.53).

3.2.3. MFI The MANOVA revealed a difference between the NOR and HYPO trials as regards the MFI (p b 0.05, η2p = 0.163). Namely, after the HYPO trial, subjects reported higher values of reduced motivation (p b 0.001), and physical (p b 0.05) and general (p = 0.05) fatigue (Fig. 1). Moreover, they perceived greater values for reduced activation and mental fatigue following the HYPO than the AIR trial, albeit the differences were not statistically significant (reduced activation: p = 0.11, mental fatigue: p = 0.09; Fig. 1).

3.2. Psychological responses

4. Discussion

3.2.1. POMS-SF The mean values of the POMS-SF subscales are presented in Table 2. The exercise trial (2) × testing time (2) repeated measures MANOVA on the POMS-SF showed an interaction (p b 0.001, η2p = 0.319), and main effects of trial (p b 0.001, η2p = 0.337) and time (p b 0.001, η2p = 0.621). Subjects were less tense prior to the HYPO than the AIR trial (p = 0.01). At the AIR post-exercise phase, a statistical tendency for lower tension (p = 0.08) was noticed. Conversely, the tension was increased after the HYPO trial (p = 0.03). Subjects felt less confused throughout the HYPO than the AIR trial (pre-exercise: p = 0.01; post-exercise: p = 0.03). In the AIR trial, they were less confused in the postexercise than the pre-exercise phase (p = 0.02); conversely, in the HYPO trial, they felt more confused post-exercise than pre-exercise (p = 0.007). Vigor was constantly lower in the HYPO than the AIR

The main findings of the study were that, in contrast to normoxic exercise, severe hypoxia during incremental exercise to exhaustion elicited negative post-exercise emotions, induced higher levels of perceived fatigue and decreased motivation. These emotional reactions _ 2 and HR were not associated with the lower PPO and peak values of VO

3.1. Cardiorespiratory responses The peak cardiorespiratory values obtained during both trials are _ 2peak was ~15% lower in the HYPO than the summarized in Table 1. VO AIR trial (p b 0.001). Likewise, PPO and peak values of PETCO2, HR and _ were SpO2 were lower in the HYPO trial (p b 0.001). Peak fR and VE

Table 1 Peak cardiorespiratory values obtained during the normoxic (AIR) and the hypoxic (HYPO; FiO2: 0.12) incremental exercise trial to exhaustion.

_ 2peak (mL·kg−1·min−1) VO _ (L·min−1) VE fR (breaths·min−1) VT (L) PETCO2 (mm Hg) PPO (W) HR (beats·min−1) SpO2 (%)

AIR trial

HYPO trial

52.4 ± 8.9 128 ± 25

43.4 ± 6.0⁎ 133 ± 24⁎

45 ± 8 2.9 ± 0.4 42.7 ± 6.0 323 ± 45 187 ± 7 92 ± 5

47 ± 8⁎ 2.9 ± 0.3 35.8 ± 5.0⁎ 271 ± 28⁎ 180 ± 7⁎ 73 ± 4⁎

_ minute ventilation, fR: respiratory _ 2peak: peak oxygen uptake, VE: Values are mean ± SD. VO frequency, VT: tidal volume, PETCO2: partial pressure of end-tidal carbon dioxide, PPO: peak power output, HR: heart rate, SpO2: capillary oxyhemoglobin saturation. ⁎ Significantly different from the AIR trial (p ≤ 0.05).

attained during the HYPO than the AIR trial, thereby providing further _ 2 and HR do not constitute the dominant support to the notion that VO

cues for effort sensation during, or immediately after maximal exercise [26–28]. The relative exercise intensity has been considered the critical sensory variable for the effort perception [26]; yet, in the present study, although, at the point of exhaustion, the relative intensity was similar in the two trials, the negative affective reaction was more profound after the HYPO trial. Ergo, current results might argue in favor of hypoxia per se as the key component mediating the post-exercise emotional state, notwithstanding any variation in the achieved maximal exercise intensity, either absolute or relative. The physiological mechanisms underlying the hypoxia-induced post-exercise affective responses are difficult to discern from the current results. Presumably, the unpleasant affects following the HYPO trial were attributable to the direct effects of hypoxia on the cerebral function, eliciting “central fatigue”; especially, in view of the evidence that, under circumstances of severe hypoxia (SpO2 b 70–75%), as in the present experiments, cerebral hypoxia per se has emerged as a critical influence curtailing exercise performance [21]. Although sensory input from the fatiguing locomotor and respiratory muscles might also constitute pivotal peripheral cues for the perception of fatigue post exercise [22,29,30], Goodall et al., [22] have recently shown that the supraspinal component of central fatigue is exacerbated after hypoxic whole-body maximal exercise, as indicated by a greater reduction in cortical voluntary activation, possibly via mechanisms that are sensitive to reduced O2 availability in the brain. Indeed, a number of studies have

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Table 2 Mean (±SD) values of the Profile Mood State-Short Form (POMS-SF) subscales obtained before and after the normoxic (AIR) and the hypoxic (HYPO; FiO2: 0.12) incremental exercise trial to exhaustion. Cronbach's a

AIR trial Pre-exercise

Tension Depression Vigor Anger Fatigue Confusion

0.74 0.88 0.89 0.75 0.73 0.73

0.92 ± 0.49 0.22 ± 0.32 2.25 ± 0.86 0.12 ± 0.15 0.49 ± 0.42 0.59 ± 0.54

HYPO trial Post-exercise

Pre-exercise

Post-exercise

0.78 ± 0.39 0.16 ± 0.21 2.19 ± 0.93 0.10 ± 0.21 1.37 ± 0.61† 0.43 ± 0.39†

0.66 ± 0.53⁎

0.90 ± 0.61†,⁎ 0.16 ± 0.23 1.57 ± 0.78⁎ 0.10 ± 0.18 1.39 ± 0.76† 0.66 ± 0.50†,⁎

0.18 ± 0.39 1.69 ± 0.71⁎ 0.17 ± 0.41 0.41 ± 0.63 0.35 ± 0.52⁎

† Significantly different from the pre-exercise (p ≤ 0.05). ⁎ Significantly different from the AIR trial (p ≤ 0.05).

demonstrated that during hypoxic exercise to exhaustion, the hyperventilation-induced hypocapnia, which was also evident in the present study, causes a reduction in the O2 delivery in the cerebral prefrontal cortex [15–20], and in the premotor and motor cortices as well [18], which in turn might induce alterations in the turnover of several brain neurotransmitters (i.e. serotonin, dopamine; cf. [31]). Hence, inasmuch as the prefrontal cerebral cortex is considered one of the main structures in a central circuit governing positive and negative affects [14], it is postulated that the negative post-exercise affective responses were wholly, or to a large extent, engendered by the hypoxiainduced cerebral perturbations. _ and fR in the HYPO trial revealed a The higher peak values of VE greater respiratory distress in this condition, which might also be linked, at least to some degree, to the negative post-exercise affects. Indeed, _ and fR are associated with there is evidence to suggest that both VE the effort perception and the emotional reactions in exercising individuals [32–35], and particularly in patients with chronic obstructive pulmonary disease (COPD) [36–38]. However, in the present study, there was no indication of any tight relation between the respiratory and perceptual responses (Table 4); apart from a moderate negative correlation _ and tension (r = −0.36; p ≤ 0.05), and reduced motivation between VE

(r = −0.41; p ≤ 0.05), and between fR and general fatigue (r = −0.37; p ≤ 0.05) and reduced motivation (r = −0.37; p ≤ 0.05). This might be explained by the fact that, when the emotional responses were moni_ and fR had likely returned to their baseline levels; therefore, tored, VE

their direct impact on the development of the post-exercise emotional state was probably limited. _ normalizes promptly after removal of the However, although VE hypoxic stimulus, some sympathoexcitation might prevail at least 20 min following the return to normoxia [39,40]. Unfortunately, no markers of sympathetic tone (i.e. arterial pressure, HR) were measured during the post-exercise phase; and whether a hypoxia-induced sympathetic activity affected the emotional responses after the HYPO trial remains uncertain. It appears less likely that the negative emotions ensued from the HYPO trial were related to the excess secretion of stress hormones (i.e. catecholamines, cortisol), in view of the evidence that peak values of these hormones do not differ between a normoxic and a hypoxic incremental exercise to exhaustion [10,41]. Yet, of interest in this regard are

the findings by Bouissou et al. [42], who have detected a lower concentration of norepinephrine during hypoxic exercise, which might be related to the negative affects following the HYPO trial, especially the reduced energy and motivation [43,44]. However, catecholamines were not measured in the present study. Furthermore, the exerciseinduced increase in oxidative stress is more profound following acute exercise in hypoxia [45,46]. That being the case, and on the basis that oxidative stress is associated with unpleasant feelings, such as emotional stress [47], oxidative stress might also be a plausible explanation for the negative post-exercise affective reactions. Still, considering that the actual level of central and peripheral fatigue was not determined in the present study, the exact physiological mechanisms related to the hypoxia-induced emotional alterations remain hypothetical, and need to be elucidated in further studies. The hypoxia-induced neuropsychological alterations are related to the level of hypoxic exposure [48]; hence, whether a moderate hypoxic stimulus during maximal exercise would induce similar emotional responses as those reported herein remains to be determined. Nevertheless, it is noteworthy that a brief exposure to severe hypoxia during maximal exercise (average time in hypoxia: 15 ± 1 min) prompts similar emotional alterations to those that have been encountered during a prolonged sojourn at high-altitude [48–51]. In this context, it is also interesting that the negative affects following the HYPO trial were apparent, despite the fact that subjects had been reinstated to the normoxic conditions. Moreover, although the existence of any physiological difference between normobaric and hypobaric hypoxia is still a subject of debate [52,53], current findings are pertinent to normobaric hypoxia setting, and to what extent they are representative of those expected in hypobaric hypoxic circumstances remains uncertain. The post-exercise affects are partly dependent on the timing of the assessment [7,54]; inasmuch as, upon the exercise cessation, an affective “rebound” from negativity to positivity often transpires, leading to a more pleasant affective state after exercise than before exercise [4]. However, even if an affective “rebound” has taken place in the present study, the negative affects and the higher levels of perceived fatigue were still evident following the HYPO trial. Yet, our work would have benefited from the assessment of affective valence and perceived arousal throughout the exercise bouts, and this needs to be considered in the design of future studies.

Table 3 Mean (±SD) values of the Activation Deactivation Check List (AD ACL) subscales obtained before and after the normoxic (AIR) and the hypoxic (HYPO; FiO2: 0.12) incremental exercise trial to exhaustion. Cronbach's a

Energy Tiredness Tension Calmness

0.83 0.54 0.69 0.77

† Significantly different from the pre-exercise (p ≤ 0.05). ⁎ Significantly different from the AIR trial (p ≤ 0.05).

AIR trial

HYPO trial

Pre-Exercise

Post-Exercise

Pre-Exercise

Post-Exercise

2.90 ± 0.63 2.18 ± 0.38 1.87 ± 0.48 2.47 ± 0.57

2.93 ± 0.72 2.46 ± 0.35† 1.81 ± 0.56 2.32 ± 0.72

2.71 ± 0.71 2.14 ± 0.33 1.71 ± 0.49 2.34 ± 0.63

2.57 ± 0.70⁎ 2.65 ± 0.31†,⁎ 2.03 ± 0.54⁎ 1.89 ± 0.61†,⁎


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normoxic conditions, while they were sitting alone and at a distance from the researchers. Lastly, although the 48-h interval between the two trials might be considered insufficient for full recovery from exercise, especially following the HYPO trial, MacNutt et al. [55] did not detect any carryover or training effect during a 17-min hypoxic exercise performed on five nonconsecutive days in a 2-week period. Nevertheless, in the present study, any risk of carryover effect was eliminated by counter-balancing the order of the trials. 4.1. Practical perspectives

Fig. 1. Mean (±SD) values of the Multidimensional Fatigue Inventory (MFI) subscales obtained after the normoxic (AIR) and the hypoxic (HYPO; FiO2: 0.12) incremental exercise trial to exhaustion. *Significantly different from the AIR trial (p ≤ 0.05). Cronbach's a for general fatigue = 0.56, physical fatigue = 0.80, reduced activation = 0.82, reduced motivation = 0.77, mental fatigue = 0.87.

A potential limitation of the study is that the breathing interventions were not blinded, and hence the possibility of any biases or placebo/ nocebo effect on subjects' responses should be considered. However, subjects were naïve as regards the hypothesis of the study; they were informed that the aim was to examine the effect of maximal exercise on their emotional responses, but were not made aware of the prospective direction of the response, or the potential effects of hypoxia. The majority of the psychological variables did not, in fact, differ between the two pre-exercise phases. Notably, although two subscales from the POMS-SF, the tension and the confusion, were higher prior to the AIR than the HYPO trial, both were altered in the opposite direction following exercise: they were increased and decreased after the HYPO and NOR trials, respectively. Furthermore, the inclusion of a control condition (NOR trial) minimized any possible Hawthorne effect; during both trials, subjects exercised on the same cycle-ergometer, and replied to the questionnaires in an identical laboratory environment under Table 4 Correlation values between the Profile of Mood States-Short Form (POMS-SF), Activation Deactivation Adjective Check List (AD ACL) and Multidimensional Fatigue Inventory (MFI) _ subscales with the peak values of minute ventilation (VE), respiratory frequency (fR) and tidal volume (VT) obtained during the normoxic (AIR) and the hypoxic (HYPO; FiO2: 0.12) incremental exercise trial to exhaustion. AIR trial

POMS-SF Tension Depression Vigor Anger Fatigue Confusion AD ACL Energy Tiredness Tension Calmness MFI General fatigue Physical fatigue Reduced activation Reduced motivation Mental fatigue ⁎ p ≤ 0.05.

HYPO trial

_ VE

fR

VT

_ VE

fR

VT

−0.32 0.07 −0.29 0.06 0.21 −0.19

−0.21 0.05 −0.13 0.05 0.04 −0.12

−0.19 0.03 −0.22 0.00 0.24 −0.15

−0.06 0.16 −0.02 0.18 0.14 0.09

0.17 0.15 −0.02 0.13 0.02 0.06

−0.29 0.05 0.06 0.09 0.18 0.05

−0.30 −0.05 −0.26 0.14

−0.18 −0.05 −0.19 −0.28

−0.19 0.05 −0.11 −0.17

−0.15 −0.25 −0.36⁎ 0.22

−0.01 −0.17 −0.12 0.26

−0.19 −0.10 −0.37⁎

−0.13 −0.15 0.08 −0.26 −0.17

−0.20 −0.14 −0.03 −0.20 −0.22

0.08 −0.02 0.12 −0.09 0.03

−0.13 −0.21 0.28 −0.41⁎

−0.37⁎ −0.16 −0.25 −0.37⁎

−0.22

−0.30

−0.10

0.27 0.02 −0.03 −0.09 0.08

Although the current study does not provide evidence as regards the limiting factors of endurance performance, in view of the notion that emotions facilitate decision making [14] and, to a certain degree, govern exercise performance [56–58], it is plausible that the development of the hypoxia-induced negative affects might impose, consciously and/ or subconsciously, a potential determinant to maximal exercise in circumstances of severe hypoxia. In addition, the understanding of emotional responses to exercise in hypoxia might provide useful information for the design of hypoxic training protocols and for the application of optimal training stimuli to prevent emotional exhaustion, and thereby fatigue/overtraining, in sportsmen and military personnel, but also in patients with chronic disease rendering them hypoxic (e.g. COPD patients). 5. Conclusions The results of the present study demonstrate that, in contrast to exercise in normoxic conditions, an incremental exercise to exhaustion performed under severe normobaric hypoxia provokes negative postexercise emotions, induces higher levels of perceived fatigue and de_ 2peak and PPO. creases motivation, despite the comparatively lower VO Hence, further investigation is needed to examine whether a regimen of hypoxic acclimatization would counter the unpleasant postexercise emotions evoked by acute hypoxia. Acknowledgements The current project was funded, in part, by the Olympic Committee and the Ministry of Defense of the Republic of Slovenia. We would like to thank all the subjects for their participation in the study. The authors state that there is no personal or financial conflict of interest in the present study. References [1] R.R. Yeung, The acute effects of exercise on mood state, J. Psychosom. Res. 40 (1996) 123–141. [2] P. Ekkekakis, G. Parfitt, S.J. Petruzzello, The pleasure and displeasure people feel when they exercise at different intensities: decennial update and progress towards a tripartite rationale for exercise intensity prescription, Sports Med. 41 (2011) 641–671. [3] P. Ekkekakis, S.J. Petruzzello, Acute aerobic exercise and affect: current status, problems and prospects regarding dose-response, Sports Med. 28 (1999) 337–374. [4] P. Ekkekakis, Pleasure from the exercising body. Two centuries of changing outlooks in psychological thought, in: P. Ekkekakis (Ed.), Routledge Handbook of Physical Activity and Mental Health, Routledge, New York 2013, pp. 35–56. [5] M. Kilpatrick, R. Kraemer, J. Bartholomew, E. Acevedo, D. Jarreau, Affective responses to exercise are dependent on intensity rather than total work, Med. Sci. Sports Exerc. 39 (2007) 1417–1422. [6] E.O. Acevedo, R.R. Kraemer, G.H. Kamimori, R.J. Durand, L.G. Johnson, V.D. Castracane, Stress hormones, effort sense, and perceptions of stress during incremental exercise: an exploratory investigation, J. Strength Cond. Res. 21 (2007) 283–288. [7] P.J. O'Connor, S.J. Petruzzello, K.A. Kubitz, T.L. Robinson, Anxiety responses to maximal exercise testing, Br. J. Sports Med. 29 (1995) 97–102. [8] H.T. Edwards, Lactic acid in rest and work at high altitude, Am. J. Physiol. 116 (1936) 367–375. [9] L.G. Pugh, M.B. Gill, S. Lahiri, J.S. Milledge, M.P. Ward, J.B. West, Muscular exercise at great altitudes, J. Appl. Physiol. 19 (1964) 431–440.

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