The presence of cardiometabolic syndrome (CMS) confers an increased risk for cardiovascular disease (CVD) and mortality and is associated with reduced health-related quality of life (HRQoL). Although the effects of exercise on biomarkers, HRQoL, and future risk have been studied, no study has measured the effects on all three components. The present study compared the effects of steady-state, moderate-intensity treadmill training (TM) and high-velocity circuit resistance training (HVCRT) on biological markers, HRQoL, and overall CVD risk in adults with CMS and CVD risk factors. Thirty participants (22 females, 8 males) were randomly assigned to 1 of 3 groups: HVCRT, TM, or control. Participants in the exercise groups attended training 3 days/week for a total of 12 weeks. Of the 30 participants who began the study, 24 (19 females, 5 males) were included in the final analysis. Primary outcome measures included CMS criteria, hemodynamic measures, Framingham Risk Score (FRS), and HRQoL. All variables were measured pre- and post-intervention. CMS z score significantly decreased for HVCRT (p = 0.03), while there were no significant changes for TM or control. FRS significantly decreased for HVCRT compared with TM (p = 0.03) and control (p = 0.03). Significant decreases in systolic (p < 0.01) and diastolic blood pressures (p < 0.01) for HVCRT accompanied significant increases from baseline in stroke volume (p = 0.03) and end-diastolic volume (p < 0.01). Systemic vascular resistance significantly decreased (p = 0.05) for HVCRT compared with control. Emotional well-being significantly improved following HVCRT and TM compared with control (p = 0.04; p = 0.03). HVCRT represents a novel training modality that improved factors in each of the 3 components assessed.

Habituation is an adaptation seen in many organisms, defined by a reduction in the response to repeated stimuli. Evolutionarily, habituation is thought to benefit the organism by allowing conservation of metabolic resources otherwise spent on sub-lethal provocations including repeated cold exposure. Hypermetabolic and/or insulative adaptations may occur after prolonged and severe cold exposures, resulting in enhanced cold defense mechanisms such as increased thermogenesis and peripheral vasoconstriction, respectively. Habituation occurs prior to these adaptations in response to short duration mild cold exposures, and, perhaps counterintuitively, elicits a reduction in cold defense mechanisms demonstrated through higher skin temperatures, attenuated shivering, and reduced cold sensations. These habituated responses likely serve to preserve peripheral tissue temperature and conserve energy during non-life threatening cold stress. The purpose of this review is to define habituation in general terms, present evidence for the response in non-human species, and provide an up-to-date, critical examination of past studies and the potential physiological mechanisms underlying human cold habituation. Our aim is to stimulate interest in this area of study and promote further experiments to understand this physiological adaptation.

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