Individuals in many occupations (i.e., law enforcement, police, firefighters) are exposed to stress stemming from a combination of psychological and high physical demands. This can result in negative health effects as shown by increase morbidity and mortality rates in firefighters and law enforcement officers 1,2.

Stress Response

The human stress response to brief periods of mental or physical stress involves hormonal responses from the hypothalamic-pituitary-adrenal (HPA) axis, resulting in the release of cortisol 3. The chronic activation of the sympathoadrenal and HPA axes can occur from psychological and physical stress that is prevalent in many occupations in modern society. The negative consequences are that this can result in cardiometabolic and psychological disturbances 4.

The psychological effects of cortisol may serve as a mechanism for negative states during stressful situations and are regarded as an index of distress, helplessness, and perceived uncontrollability 5. Cortisol is a catabolic hormone and stimulates gluconeogenesis, acts as an anti-inflammatory agent and depresses the immune system. The cumulative interaction of stress hormones resulting from combined physical and psychological stress is proposed to increase the risk of cardiovascular, metabolic, and immunological disorders 4.

Increasing cardiorespiratory (CR) fitness is recommended as an interventional strategy to reduce these risks due to its demonstrated benefit in lowering cortisol response 6. Studies suggest that individuals with higher CR should have less exacerbated cortisol response to mental and physical stress compared with lower fit individuals, although it is unknown whether higher fitness levels can reduce the aggravated cortisol responses seen in concurrent physical and mental stressful situations.

The Study

A collaborative research study was conducted to examine state anxiety, effort sense, and cortisol responses between lower fitness (LF) and higher-fitness (HF) level individuals exercising at the same relative intensities while exposed to a mental challenge 7. These researchers hypothesized that LF individuals would perceive the stressful challenge as more anxiety producing and would result in unfavorable cortisol responses when compared with that of HF individuals.

The HF individuals were recruited from university sports clubs and teams (i.e., triathlon, crew) and exercised an average of 6 days/week for a minimum of 90 min per day. LF individuals did not conduct formal exercise training and were mostly sedentary. After initial testing for VO2 max to assess cardiorespiratory fitness, participants conducted a dual challenge condition (DCC) and an exercise-alone condition (EAC) which both consisted of moderate-intensity cycling at 60% VO2 max for 37 min. In addition to exercise, the DCC included participation in a mental challenge while cycling from minute 12 until 32 min.

The Results

Results demonstrated that the DCC resulted in an increase in state anxiety, perceived overall workload, and exacerbated cortisol responses. Furthermore, the LF participants had a greater overall cortisol response in the DCC compared with the EAC whereas the HF participants demonstrated no difference between conditions. This finding suggests that the HPA axis responses to stress may be sensitive to CR fitness level.

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How many days a week should I do Max-OT Cardio?

This study is the first to demonstrate differences in cortisol responses to concurrent mental and physical challenge between aerobically high-fit and low-fit individuals. Given the catabolic function of cortisol, prolonged cortisol activation has deleterious consequences such as decreasing lean body mass, increasing fat mass and causing insulin resistance, as well as contributing to cardiovascular disease 8. It is important to inform individuals exposed to combined challenges of physical and mental stress that CR fitness level is crucial to coping with occupational stressors. The cortisol responses in this study suggest that a high level of fitness may provide another benefit not previously described in the scientific literature. More research is needed to determine what the minimum CR level is needed to obtain these benefits.

This is just another one of the many benefits of exercise! I recommend utilizing Max-OT Cardio which maximizes training intensity to take advantage of your body’s physiological response. Training with ultra-high intensity for shorter periods of time increases your body’s overall metabolic rate burning more fat 24-hours a day without sacrificing lean muscle!


1. Franke WD, Kohut ML, Russell DW, Yoo HL, Ekkekakis P, Ramey SP. Is job-related stress the link between cardiovascular disease and the law enforcement profession? J Occup Environ Med 2010;52:561-5.
2. Kales SN, Soteriades ES, Christophi CA, Christiani DC. Emergency duties and deaths from heart disease among firefighters in the United States. N Engl J Med 2007;356:1207-15.
3. Besedovsky HO, del Rey A. The cytokine-HPA axis feed-back circuit. Z Rheumatol 2000;59 Suppl 2:II/26-30.
4. Chrousos GP. Stress and disorders of the stress system. Nat Rev Endocrinol 2009;5:374-81.
5. Dienstbier RA. Arousal and physiological toughness: Implications for mental and physical health. Psychol Rev 1989;96:84-100.
6. Rimmele U, Seiler R, Marti B, Wirtz PH, Ehlert U, Heinrichs M. The level of physical activity affects adrenal and cardiovascular reactivity to psychosocial stress. Psychoneuroendocrinology 2009;34:190-8.
7. Webb HE, Rosalky DS, Tangsilsat SE, McLeod KA, Acevedo EO, Wax B. Aerobic fitness affects cortisol responses to concurrent challenges. Med Sci Sports Exerc 2013;45:379-86.
8. Christiansen JJ, Djurhuus CB, Gravholt CH, et al. Effects of cortisol on carbohydrate, lipid, and protein metabolism: studies of acute cortisol withdrawal in adrenocortical failure. J Clin Endocrinol Metab 2007;92:3553-9.

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High-Level Cardio Science

by Paul C. Henning, Ph.D. CSCS time to read: 4 min