|Year : 2018 | Volume
| Issue : 2 | Page : 83-88
Role of the work-to-rest ratio in high-intensity interval exercise on heart rate variability and blood pressure in sedentary obese men
Abdullah F Al-Fehaid1, Shaea A Alkahtani2, Ahmed A Al-Sunni3, Talay Yar3
1 Department of Physiotherapy, Hospital of Dammam, Dammam, Saudi Arabia
2 Department of Exercise Physiology, College of Sport Sciences and Physical Activity, King Saud University, Riyadh, Saudi Arabia
3 Department of Physiology, College of Medicine, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia
|Date of Web Publication||1-Oct-2018|
Dr. Shaea A Alkahtani
Department of Exercise Physiology, College of Sport Sciences and Physical Activity, King Saud University, Riyadh
Source of Support: None, Conflict of Interest: None
Objective: The effect of different durations of high-intensity interval exercise (HIIE) on heart rate (HR) variability (HRV) and blood pressure (BP) in obese men. Materials and Methods: The study was a repeated measure and conducted in a counterbalanced order. Fifteen young obese men participated in five exercise tests on a cycle ergometer as follows: (a) graded exercise test to determine exercise intensity, (b) constant-load exercise test at 40% of HR reserve (HRR) for 20 min, (c) the 30:30 HIIE protocol at 80% of HRR (30 s of exercise followed by 30-s recovery intervals for 20 min), (d) the 60:60 HIIE protocol at 80% of HRR for 20 min, and (e) the 60:30 HIIE protocol at 80% of HRR for 15 min. HRV and BP were recorded before exercise, at the end of exercise, and at 30 min after exercise. Participants also provided feedback regarding the pleasure and excitement to exercise. Results: HRV recovery was greater in the 30:30 HIIE protocol and lesser in the 60:30 HIIE protocol. The mean arterial BP exhibited postexercise hypotension. Peak rate pressure product during exercise was highest in the 60:30 protocol and lowest in the 30:30 protocol. The participants preferred the 60:60 HIIE protocol in terms of pleasure and excitement. Conclusions: Interval exercise of 1:1 ratio model is recommended over the 2:1 ratio for obese men, with better physiological responses to the 30:30 HIIE protocol and better psychological responses to the 60:60 HIIE protocol.
Keywords: Blood pressure, heart rate variability, high-intensity interval exercise, obese men
|How to cite this article:|
Al-Fehaid AF, Alkahtani SA, Al-Sunni AA, Yar T. Role of the work-to-rest ratio in high-intensity interval exercise on heart rate variability and blood pressure in sedentary obese men. Saudi J Health Sci 2018;7:83-8
|How to cite this URL:|
Al-Fehaid AF, Alkahtani SA, Al-Sunni AA, Yar T. Role of the work-to-rest ratio in high-intensity interval exercise on heart rate variability and blood pressure in sedentary obese men. Saudi J Health Sci [serial online] 2018 [cited 2019 May 20];7:83-8. Available from: http://www.saudijhealthsci.org/text.asp?2018/7/2/83/242495
| Introduction|| |
The imbalance between the two divisions of the autonomic nervous system (ANS) is considered a major cause of cardiac diseases. Reduced vagal activity and enhanced sympathetic activity are unfavorable autonomic patterns. Changes in ANS balance affect heart rate (HR), blood pressure (BP), and HR variability (HRV)., Autonomic function can be assessed noninvasively by monitoring HR, BP, and HRV responses. High resting HR (RHR) and low HRV are associated with impaired functional status and independent of cardiovascular disease. Rate pressure product (RPP) reflects the internal myocardial work performed by the heart and is defined as the product of HR and systolic BP (SBP). This simply calculated index is correlated with myocardial oxygen consumption and reflects the response of the coronary circulation to myocardial metabolic demand.
Obesity is a major factor that influences BP and HRV during rest and exercise. Evidence indicates that in obese adults as compared with normal-weight adults, arterial pressure response to physical exertion is augmented, which is an indicator of cardiovascular risk., Muscle sympathetic activity increases consistently in obese adults when compared with that in nonobese individuals,, which can partially be attributed to hyperleptinemia. Despite an increased muscle sympathetic activity at rest, the sympathetic response to exercise is blunted., Furthermore, HRV is reduced in sedentary individuals who also show increased RHR., Postexercise parasympathetic reactivation seems to be influenced by resting vagal control, whereby participants characterized by higher vagal modulation at rest tend to exhibit better parasympathetic reactivation and faster HR recovery. A diminished HR response during exercise recovery was significantly correlated with a resting sympathetic activity overload.
Exercise training has been shown to enhance vagal modulation, improve HRV, and reduce sympathetic outflow and plasma levels of catecholamine at rest. High-intensity interval exercise (HIIE) has been advocated for its health benefits. HIIE has different models, most of which stem from studies conducted with elite athletes or well-trained individuals. As obese individuals usually find training at maximal levels less tolerable than moderate-intensity training, the optimal tolerable intensity and duration should be selected for obese individuals. The optimal intensity of HIIE for obese and sedentary individuals has been studied. For example, HRV was measured in 13 young male volunteers after two exercise sessions at 50% and 80% of oxygen consumption reserve (VO2R). Low-intensity exercise caused small shifts in cardiac autonomic balance with a quicker restoration of vagal modulation than that in high-intensity exercise. Moreover, parasympathetic function was activated in 10 min at 50% of VO2R and in 25 min at 80% of VO2R. At equivalent workloads, HRV was lower during continuous exercise than during interval intervention, and high-intensity exercise elicited a lower HRV in the postexercise period. HRV after supramaximal sprint interval exercise tends to recover within 1–2 h, indicating that the risk of cardiac events may be increased after such exercise. It appears that submaximal intensity of interval exercise may be recommended for sedentary and obese individuals. In addition, the short duration of interval exercise protocols allows individuals to complete a longer interval exercise session, with low metabolic demands, but the optimal duration of work-to-rest interval ratio in terms of ANS responses is unclear. Thus, the objective of this study was to determine the effect of different short work-to-rest ratios of HIIE on HR, BP, and HRV in young sedentary obese men.
| Materials and Methods|| |
Fifteen sedentary overweight/obese Saudi men from the student population of the Imam Abdulrahman Bin Faisal University and other colleges in the region were recruited (mean ± standard deviation [SD]: age, 21 ± 1.6 years; body mass index, 34.6 ± 5.7 kg/m2; waist circumference, 107 ± 13.7 cm). The exclusion criteria were any systemic disease, including cardiovascular diseases, respiratory problems, diabetes mellitus, hypertension, and medication use. It also included any bone and joint problems or any lower extremity injury that hinders exercise. Smokers were also excluded from the study.
The study was performed at the laboratory of the Department of Physiology of Imam Abdulrahman Bin Faisal University, Saudi Arabia. Ethics approval was obtained from the internal review board of Imam Abdulrahman Bin Faisal University (IRB 2013-308). All the participants signed a written consent form in the first visit, after receiving a full explanation of the study procedure. All the measurements were performed according to a standardized protocol, between 9:30 am and 11:30 am in the laboratory, at a stable controlled temperature of 21°C ± 1°C and relative humidity of 60% ± 5%. The participants were asked to avoid strenuous exercise 24 h before the exercise tests and to abstain from energy drinks and caffeine on the day before the exercise tests.
This was an experimental study using repeated measure design. All the participants performed five exercise sessions on a computer-controlled bike with an electrical brake (Monark 839E-Sweden). Apart from the first session, the duration of each of the other sessions was 20 min, starting with a 5-min warm-up ending with a 5-min cooldown. Before beginning the exercise sessions, HR, BP, and HRV with deep breathing (HRVdb) were measured. The readings were continued after 30 min of exercise cessation. The participants were instructed to have at least 6 h of sleep the night before the exercise tests and take a light breakfast in the morning.
The first session was performed to determine the maximal HR (HRmax) and exercise intensities for the subsequent protocols. After performing a 5-min warm-up at 20 W, the participants maintained a cadence of 65 revolutions per min against a cycling load that was increased by 20 W at each 1-min stage until volitional exhaustion within ± 10% of the predicted HRmax.
HR reserve (HRR) was used to determine the exercise intensities at 40% and 80% of HRR and was calculated using the Karvonen formula as follows: HR = (% of target intensity × (HRmax− HRrest) + HRrest. Moreover, HR was continuously monitored through the HR displayed on the computer derived from the Polar chest belt in all exercise sessions. Respiratory rate was also recorded through the respiratory belt, and these devices were connected to the computer through PowerLab 8/35 (ADInstruments, Australia).
Four exercise sessions were performed in a random order and included a constant-load exercise test at 40% of HRR for 20 min. The remaining three interval exercise tests included HIIE for 30 s at 80% of HRR followed by 30-s passive rest intervals repeated 20 times for 20 min (the 30:30 protocol), HIIE for 1 min at 80% of HRR followed by 1-min passive rest intervals repeated 10 times for 20 min (the 60:60 protocol), and HIIE for 1 min at 80% of HRR followed by 30-s passive rest intervals repeated 10 times for 15 min (the 60:30 protocol).
Measurement of heart rate variability with deep breathing
The participants were instructed to take six deep breaths throughout 1 min before and after the exercise sessions to assess the HRV during the respiration cycles (HRVdb). HRVdb was computed by calculating the expiratory-to-inspiratory ratio (E/I ratio), which is the ratio of between the longest R-R interval during expiration and the shortest R-R interval during inspiration; mean HR range (MHRR), which is the difference between the HRmax during inspiration and the minimal HR during expiration; and mean percentage variation in HR (M%VHR), which is the mean percentage of HR variation over the six deep breaths.
Measurement of finger blood pressure
BP during exercise was measured using Finometer (Model 1.FM.1.MU.00795; Finapres Medical Systems, Amsterdam). Owing to the excessive movements, stable recording was not possible throughout the exercise sessions. Nevertheless, small intervals of recording were possible at some points in time during the latter part of the sessions, where we could record the maximum pressures while the participant was exercising. The Finometer uses the volume-clamp method to measure BP in the finger. Changes in arterial diameter, detected by means of an infrared photoplethysmograph built-in in the finger cuff, are opposed by a fast pressure servo controller that changes pressure in an inflatable air bladder.
Measurement of rate pressure product
The RPP is an indirect measure of the myocardial workload/myocardial oxygen demand. It is calculated by multiplying the SBP by the HR.
Pleasure and excitement in exercise
At the end of the last exercise session (fifth session), the participants were asked, “Which exercise was the most pleasant to perform?” and “Which exercise was the most exciting?”
Statistical analysis was performed using the Statistical Package of the Social Science (SPSS), SPSS Inc., IBM Corporation, version 20, New York, USA. Data were presented as means ± SD. A comparison between rest values in all the exercise days was analyzed using analysis of variance (ANOVA). The interaction between the HIIE protocol and pre-post changes in study variables was analyzed using the univariate ANOVA. The level of significance was set at P < 0.05.
| Results|| |
No significant differences in HRVdb were found between the different exercise protocols at preexercise sessions, as determined based on E/I ratio, MHRR, and M%VHR. A significant reduction in HRVdb recorded at 30 min after exercise was observed when compared with the respective preexercise value as indicated by the E/I ratio and M%VHR. The difference was significant only in the 60:30 HIIE protocol when the MHRR criteria were used. However, no significant differences in HRVdb at 30 min after the exercise sessions in terms of E/I ratio, MHRR, and M%VHR were found between all the exercise protocols. The univariate ANOVA revealed that the interaction between the HIIE tests and pre-post exercise HRV was based on E/I ratio (P = 0.9), based on MHRR (P = 0.09), and based on M%VHR [P = 0.9; [Table 1].
|Table 1: Heart rate variability with deep breathing in pre- and post-high-intensity interval exercise tests|
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[Table 2] shows that all exercise protocols induced significant increases in BP parameters, but the maximum changes occurred in the 60:30 protocol. BP parameters returned toward their baseline values in all the protocols, whereas postexercise HR was significantly higher than RHR in the 60:30 protocol (P ≤ 0.001).
|Table 2: Comparison of heart rate and blood pressure in pre- and post-high-intensity interval exercise tests|
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The differences in RPP at rest time between the protocols, ranging from 9.78 ± 2.13 in the 30:30 protocol to 10.08 ± 1.77 in the 60:60 protocol, were not significant. The difference in peak RPP (PRPP) between the 60:30 and 60:60 protocols during exercise was not significant, whereas PRPP for the 30:30 protocol (28.8 ± 3.5) was significantly lower than those for both protocols (P < 0.001) and was similar to that for the constant exercise protocol (27.5 ± 3.15; P = 0.451). Both HR and SBP during exercise were higher in the longer protocols (60 s) than in the short protocol (30 s). Constant exercise elicited a slightly lower HR, leading to a lower PRPP. The RPP at 30 min postexercise was higher than that at rest in all the protocols, and the difference was significant only in the 60:30 protocol [11.39 vs. 9.77, P = 0.025; [Figure 1].
|Figure 1: Peak rate pressure product before, during, and 30 minutes after constant-load exercise and high-intensity interval exercise protocols. *Significant difference at P < 0.05|
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[Figure 2] shows that most of the participants preferred the 60:60 protocol and found it to be the most pleasant and exciting to perform.
|Figure 2: Distribution of the 15 participants according to responses about the most pleasant and exciting exercise|
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| Discussion|| |
The present study aimed to compare the effects of different interval exercise ratio models, namely 1:1 either short (30:30 s) or long (60:60 s) and 2:1 (60:30 s), on HR, BP, and HRV in young obese men. The postexercise HRV recovery was maximum at 30 min postexercise in the 30:30 protocol. The 60:30 protocol exhibited the least recovery as evidenced by the significantly lower E/I ratio and M%VHR at 30 min than at rest. The SBP, diastolic BP (DBP), and mean arterial BP recovered to the same extent in all the protocols. PRPP was highest in the 60:30 protocol and lowest in the 30:30 protocol, indicating greater myocardial oxygen demand in the 60:30 protocol. RPP was significantly higher at 30 min after exercise only in the 60:30 protocol. In addition, the present obese participants preferred the 60:60 protocol in terms of convenience and excitement.
The RHRVdb parameters for the present obese participants were within their normal range, indicating that none of the participants had gross autonomic disturbance. The E/I ratio was 1.43 ± 0.22, which was above the minimal value of 1.23 for the same age group., Similarly, the MHRR was 15 bpm, which is higher than the minimal value for 20–30-year-old healthy individuals. The M%VHR was 33.11%, which is higher than the normal M%VHR reported in the literature (approximately 30%, with a range from 15% to 40%) in young individuals. Furthermore, no significant difference in HRVdb parameters was found in the preexercise period in the four exercise sessions. This was a reassurance that day-to-day variation in HRV did not affect the baseline recording of HRV parameters in the present study. The postexercise HRVdb also did not significantly differ between the study protocols. The postexercise HRVdb recovered maximally toward the baseline level in the 30:30 protocol, whereas the 60:30 protocol appears to require the longest period among the study protocols, as indicated by the E/I ratio, MHRR, and M%VHR.
The present data revealed that the 2:1 model (60:30 s) magnified the responses of HR to a greater extent than the 1:1 model, either short (30:30 s) or long (60:60 s), during exercise and in the postexercise period. Prolonged stages of interval exercise have been suggested to increase HR and blood lactate levels. HR, ventilation, oxygen consumption, and blood lactate levels were higher in the 2:1 ratio model (40:20 s) than the 1:1 ratio model (30:30 s). SBP, DBP, and mean arterial BP recovered to the same extent in all the protocols. Further decreases in SBP and DBP, termed as postexercise hypotension (PEH), were observed in the postexercise period in the 60:60 and 60:30 protocols, but the difference between the preexercise and 30-min postexercise periods was not statistically significant. PEH has previously been observed in HIIE, but the exact mechanism of this peripheral vasodilatation is not completely understood. Any reduction >3 mmHg is clinically significant.,, Clinical PEH (i.e., >3 mmHg) was observed for SBP and DBP after HIIE (10 and 15 repetitions of 1 min at 90%–95% HRmax) in 20 young normotensive untrained obese women. It is important that RHR was equal in all day sessions, which means that the participants had adequate and complete proper rest before the commencement of the exercise session. The day-to-day variation in BP is a possible interpretation of increased BP before exercise at 60:60 and 60:30 protocols, but this was not examined in the present study.
RPP at rest was comparable in the four sessions. RPP at the 30-min postexercise period remained higher than that at rest, with a significant difference only in the 60:30 protocol. The highest PRPP was observed in the 60:30 protocol, followed by the 60:60 and 30:30 protocols, in this order. The observed RPP reserve (difference between the baseline RPP and PRPP) was greater in the 60:30 protocol. The 2:1 model such as the 60:30 protocol has to be prescribed with caution, as it might trigger a decompensation of the heart in fragile obese individuals who have myocardial insufficiency.
Prescription of exercise should take into account whether a certain level of exercise intensity would likely cause increases or decreases in pleasure. The greater enjoyment associated with HIIE may be relevant for improving exercise adherence. The present obese individuals preferred the 60:60 protocol in terms of pleasure and excitement, while the least preferred protocol was the 60:30 protocol, indicating that the 1:1 model of HIIE is more preferred than the 2:1 model. Future studies are advised to examine the role of the number of stages, such as 20 versus 10 repetitions for the same exercise duration.
Limitations of this study included the inability to measure ANS activity during exercise and within the first 1–2 min of the postexercise period. HRVdb could only be recorded at a breathing rate of 6/min, which was possible only under resting conditions. Future studies are advised to include HRV and BP responses during a period longer than 60:60 s, such as 2-min intervals, but investigators should be certain that the participants are sedentary obese. Our pilot study of sedentary obese participants showed that they could not tolerate completing exercise over a period longer than a 60-s interval.
| Conclusions|| |
Although HRVdb after the exercises did not differ between the study interval protocols, BP and RPP were elevated more during the 2:1 interval model as apparent in the 60:30 protocol. The 60:60 protocol was also the most pleasant and exciting. Thus, individuals who are prone to hypertension such as the obese population are recommended to perform interval exercise consisting of the 1:1 model such as the 30:30 and 60:60 protocols, which provided obese individuals with an exciting and convenient experience.
Adherence to the study protocols by all the participants is highly appreciated.
Financial support and sponsorship
This study was possible with the support grant from the Deanship of Scientific Research at Imam Abdulrahman Bin Faisal University. This study was also supported by a grant from the Research Centre for the Sport Sciences and Physical Activity, Deanship of Scientific Research at King Saud University, for Dr. Alkahtani.
Conflicts of interest
There are no conflicts of interest.
| References|| |
Munk PS, Butt N, Larsen AI. High-intensity interval exercise training improves heart rate variability in patients following percutaneous coronary intervention for angina pectoris. Int J Cardiol 2010;145:312-4.
Levy WC, Cerqueira MD, Harp GD, Johannessen KA, Abrass IB, Schwartz RS, et al.
Effect of endurance exercise training on heart rate variability at rest in healthy young and older men. Am J Cardiol 1998;82:1236-41.
Singh JP, Larson MG, Tsuji H, Evans JC, O'Donnell CJ, Levy D. Reduced heart rate variability and new-onset hypertension: Insights into pathogenesis of hypertension: The Framingham heart study. Hypertension 1998;32:293-7.
Ogliari G, Mahinrad S, Stott DJ, Jukema JW, Mooijaart SP, Macfarlane PW, et al.
Resting heart rate, heart rate variability and functional decline in old age. CMAJ 2015;187:E442-9.
Gobel FL, Norstrom LA, Nelson RR, Jorgensen CR, Wang Y. The rate-pressure product as an index of myocardial oxygen consumption during exercise in patients with angina pectoris. Circulation 1978;57:549-56.
Ansari M, Javadi H, Pourbehi M, Mogharrabi M, Rayzan M, Semnani S, et al.
The association of rate pressure product (RPP) and myocardial perfusion imaging (MPI) findings: A preliminary study. Perfusion 2012;27:207-13.
Dipla K, Nassis GP, Vrabas IS. Blood pressure control at rest and during exercise in obese children and adults. J Obes 2012;2012:147385.
Mariampillai JE, Engeseth K, Kjeldsen SE, Grundvold I, Liestøl K, Erikssen G, et al
. 2D.01: Exercise systolic blood pressure >/=190 mmhg at moderate workload predicts coronary heart disease in healthy, middle-aged men. J Hypertens 2015;33 Suppl 1:e28.
Mundal R, Kjeldsen SE, Sandvik L, Erikssen G, Thaulow E, Erikssen J. Exercise blood pressure predicts mortality from myocardial infarction. Hypertension 1996;27:324-9.
Prior LJ, Davern PJ, Burke SL, Lim K, Armitage JA, Head GA. Exposure to a high-fat diet during development alters leptin and ghrelin sensitivity and elevates renal sympathetic nerve activity and arterial pressure in rabbits. Hypertension 2014;63:338-45.
Prior LJ, Eikelis N, Armitage JA, Davern PJ, Burke SL, Montani JP, et al.
Exposure to a high-fat dietalters leptin sensitivity and elevates renal sympathetic nerve activity and arterial pressure in rabbits. Hypertension 2010;55:862-8.
Esler M, Lambert G, Vaz M, Thompson J, Kaye D, Kalff V, et al.
Central nervous system monoamine neurotransmitter turnover in primary and obesity-related human hypertension. Clin Exp Hypertens 1997;19:577-90.
Ribeiro MM, Trombetta IC, Batalha LT, Rondon MU, Forjaz CL, Barretto AC, et al.
Muscle sympathetic nerve activity and hemodynamic alterations in middle-aged obese women. Braz J Med Biol Res 2001;34:475-8.
Karpoff L, Vinet A, Schuster I, Oudot C, Goret L, Dauzat M, et al.
Abnormal vascular reactivity at rest and exercise in obese boys. Eur J Clin Invest 2009;39:94-102.
Stutzman SS, Brown CA, Hains SM, Godwin M, Smith GN, Parlow JL, et al.
The effects of exercise conditioning in normal and overweight pregnant women on blood pressure and heart rate variability. Biol Res Nurs 2010;12:137-48.
Albinet CT, Boucard G, Bouquet CA, Audiffren M. Increased heart rate variability and executive performance after aerobic training in the elderly. Eur J Appl Physiol 2010;109:617-24.
Iellamo F, Legramante JM, Massaro M, Raimondi G, Galante A. Effects of a residential exercise training on baroreflex sensitivity and heart rate variability in patients with coronary artery disease: A randomized, controlled study. Circulation 2000;102:2588-92.
Cunha FA, Midgley AW, Gonçalves T, Soares PP, Farinatti P. Parasympathetic reactivation after maximal CPET depends on exercise modality and resting vagal activity in healthy men. Springerplus 2015;4:100.
Gademan MG, Swenne CA, Verwey HF, van der Laarse A, Maan AC, van de Vooren H, et al.
Effect of exercise training on autonomic derangement and neurohumoral activation in chronic heart failure. J Card Fail 2007;13:294-303.
Gaesser GA, Angadi SS. High-intensity interval training for health and fitness: Can less be more? J Appl Physiol (1985) 2011;111:1540-1.
Ekkekakis P, Lind E. Exercise does not feel the same when you are overweight: The impact of self-selected and imposed intensity on affect and exertion. Int J Obes (Lond) 2006;30:652-60.
Parekh A, Lee CM. Heart rate variability after isocaloric exercise bouts of different intensities. Med Sci Sports Exerc 2005;37:599-605.
Kaikkonen P, Rusko H, Martinmäki K. Post-exercise heart rate variability of endurance athletes after different high-intensity exercise interventions. Scand J Med Sci Sports 2008;18:511-9.
Stuckey MI, Tordi N, Mourot L, Gurr LJ, Rakobowchuk M, Millar PJ, et al.
Autonomic recovery following sprint interval exercise. Scand J Med Sci Sports 2012;22:756-63.
Zuniga JM, Berg K, Noble J, Harder J, Chaffin ME, Hanumanthu VS. Physiological responses during interval training with different intensities and duration of exercise. J Strength Cond Res 2011;25:1279-84.
Astrand I, Astrabnd PO, Christensen EH, Hedman R. Intermittent muscular work. Acta Physiol Scand 1960;48:448-53.
Shields RW Jr. Heart rate variability with deep breathing as a clinical test of cardiovagal function. Cleve Clin J Med 2009;76 Suppl 2:S37-40.
May O, Arildsen H, Møller M. Parasympathetic function during deep breathing in the general population: Relation to coronary risk factors and normal range. J Intern Med 1999;245:287-94.
Low PA, Denq JC, Opfer-Gehrking TL, Dyck PJ, O'Brien PC, Slezak JM. Effect of age and gender on sudomotor and cardiovagal function and blood pressure response to tilt in normal subjects. Muscle Nerve 1997;20:1561-8.
Rozenek R, Funato K, Kubo J, Hoshikawa M, Matsuo A. Physiological responses to interval training sessions at velocities associated with [Latin capital v with dot above] o2max. J Strength Cond Res 2007;21:188-92.
Nicolò A, Bazzucchi I, Lenti M, Haxhi J, Scotto di Palumbo A, Sacchetti M. Neuromuscular and metabolic responses to high-intensity intermittent cycling protocols with different work-to-rest ratios. Int J Sports Physiol Perform 2014;9:151-60.
Cote AT, Bredin SS, Phillips AA, Koehle MS, Warburton DE. Greater autonomic modulation during post-exercise hypotension following high-intensity interval exercise in endurance-trained men and women. Eur J Appl Physiol 2015;115:81-9.
Bonsu B, Terblanche E. The training and detraining effect of high-intensity interval training on post-exercise hypotension in young overweight/obese women. Eur J Appl Physiol 2016;116:77-84.
Park S, Rink L, Wallace J. Accumulation of physical activity: Blood pressure reduction between 10-min walking sessions. J Hum Hypertens 2008;22:475-82.
von Känel R. Accumulation of 30 min of moderately intense physical activity is a clinically meaningful treatment to reduce systolic blood pressure in prehypertension. J Hum Hypertens 2008;22:444-6.
Ekkekakis P, Parfitt G, Petruzzello SJ. 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 2011;41:641-71.
Bartlett JD, Close GL, MacLaren DP, Gregson W, Drust B, Morton JP. High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: Implications for exercise adherence. J Sports Sci 2011;29:547-53.
[Figure 1], [Figure 2]
[Table 1], [Table 2]