The effects of high-intensity intermittent exercise training on cardiovascular response to mental and physical challenge

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Abstract

The purpose was to examine the effect of a 12-week exercise intervention on the cardiovascular and autonomic response of males to mental and physical challenge. Thirty four young overweight males were randomly assigned to either an exercise or control group. The exercise group completed a high-intensity intermittent exercise (HIIE) program three times per week for 12 weeks. Cardiovascular response to the Stroop task was determined before and after the intervention by assessing heart rate (HR), stroke volume (SV), arterial stiffness, baroreflex sensitivity (BRS), and skeletal muscle blood flow. The exercise group improved their aerobic fitness levels by 17% and reduced their body weight by 1.6 kg. Exercisers compared to controls experienced a significant reduction in HR (p < 0.001) and a significant increase in SV (p < 0.001) at rest and during Stroop and exercise. For exercisers, arterial stiffness significantly decreased at rest and during Stroop (p < 0.01), whereas BRS was increased at rest and during Stroop (p < 0.01). Forearm blood flow was significantly increased during the first two minutes of Stroop (p < 0.05). HIIE induced significant cardiovascular and autonomic changes at rest and during mental and physical challenge after 12 weeks of training.

Highlights

► Heart rate during Stroop was reduced after 12 weeks of HIIE. ► Stroke volume during Stroop increased after 12 weeks of HIIE. ► Arterial stiffness during Stroop was improved after 12 weeks of HIIE. ► Baroreflex sensitivity during Stroop was enhanced after 12 weeks of HIIE. ► Forearm blood flow during Stroop was enhanced after 12-weeks of HIIE.

Introduction

The traditional cardiovascular risk factors of smoking, obesity, diabetes, physical inactivity, and family history predict about 50% of the variance of new cardiovascular disease cases (World Health Organization, 2011), therefore, a number of other risk factors must contribute to cardiovascular disease development. One such factor is psychological stress which has been identified as playing a role in the development of cardiovascular disease (Chida and Steptoe, 2010). An exaggerated cardiovascular response to laboratory stressors such as mental arithmetic and the Stroop color-word task has been shown to have a small but significant contribution of about 2% to the future development of hypertension (Carroll et al., 2001, Carroll et al., 2003).

As regular aerobic exercise has been shown to reduce cardiovascular reactivity to acute exercise it has been proposed that exercise participation can also decrease cardiovascular reactivity to mental challenge (Boutcher and Hamer, 2006). Several longitudinal studies have reported a significant reduction in cardiovascular reactivity (Blumenthal et al., 1991, Georgiades et al., 2000), however, these results have been obtained from populations with initially elevated cardiovascular reactivity to mental challenge such as hypertensive and Type A individuals. With regard to studies using normotensive participants, changes in heart rate (HR) and blood pressure (BP) have been recorded. For example, Forcier et al., (2006) conducted a meta-analysis and found that aerobically fit individuals showed significantly attenuated HR (1.84 bpm) and systolic BP reactivity (3.69 mm Hg) and a trend toward attenuated diastolic BP reactivity (1.2 mm Hg).

These results have been derived mainly from studies using steady state aerobic exercise (e.g., cycling, jogging, and swimming). Thus, the effects of other types of exercise such as regular resistance and anaerobic training on cardiovascular reactivity are undetermined. High-intensity intermittent exercise (HIIE), a form of anaerobic training (Boutcher, 2011), involves repeated short bouts of high-intensity exercise interspersed with recovery periods (light exercise). It has been shown that HIIE, compared to steady state exercise, produces a significantly greater impact on the autonomic nervous system (ANS) assessed by HR and plasma catecholamine levels (Trapp et al., 2007). Given that HIIE induces a significant acute cardiovascular response it is feasible that HIIE training will also produce greater adaptations in ANS control of the cardiovascular system. HIIE sessions are also typically much shorter than aerobic exercise sessions and this reduced time commitment is likely to be appealing to individuals interested in improving cardiovascular health. To date, however, no study has examined the effect of HIIE training on cardiovascular response during mental and physical challenge.

Although the effects of aerobic exercise training on HR and BP response to mental challenge have been extensively studied, relatively less attention has been devoted to other aspects of cardiovascular response such as skeletal muscle blood flow and baroreceptor sensitivity (BRS). In addition, the effect of HIIE training on arterial stiffness during mental challenge has yet to be studied. Consequently, it is not clear whether autonomic control of the heart determined by BRS and arterial stiffness under mental and physical challenge is influenced by HIIE training. Therefore, the purpose of this study was to examine the effects of HIIE, repeated three times per week for 12 weeks, on multiple measures of cardiovascular and autonomic reactivity. It was hypothesized that a program of HIIE would result in significant reductions in the reactivity response during both mental and physical challenge of young, inactive men.

Section snippets

Participants

Males aged 18–35 years and BMI 25–35 kg·m2 were invited to participate through advertisements placed on the notice boards of public areas and student magazines (Table 1). Participants were non-smokers, physically inactive, free of any type of cardiovascular and pulmonary disease, and were not taking any medication. The initial participant pool was 41 with 21 participants being randomly allocated to an exercise intervention group and 20 to a control group. For various reasons such as job

Participant characteristics

There were no significant differences between the two groups on any measured variable prior to the training program (Table 1). There was, however, a significant decrease in body weight and waist circumference for the HIIE compared to the control group (p < 0.01) after the exercise intervention and a significant 17% increase (p < 0.001) in V˙O2peak (Table 1). All participants completed all 36 sessions of HIIE training. The average HR and rating of perceived exertion (RPE) during HIIE training for

Discussion

Twelve weeks of HIIE significantly increased V˙O2peak and significantly reduced body weight and waist circumference. Significant differences in cardiovascular and autonomic levels during mental and physical challenge were also found. Specifically, exercisers compared to controls experienced a significant reduction in absolute HR and RPP and a significant increase in absolute SV during both Stroop and a bout of acute cycling exercise. Exercisers compared to controls also showed decreased

Grants

We wish to thank Diabetes Australia for supporting this project (Grant #RM06599).

Disclosures

None of the authors had a personal or financial conflict of interest.

Acknowledgments

We would like to thank Lucas Webb for help with data collection.

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    Diabetes Australia supported this project (grant #RM06599).

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