Regular physical exercise, particularly aerobic exercise, has been frequently associated with improved cardiovascular performance and reduced risk of mortality.[1-3] Previous evidence suggests that carotid artery compliance is improved in healthy men and women who perform habitual aerobic exercise compared with sedentary adults, whereas 3 months of moderate-intensity aerobic exercise in previously sedentary middle-aged or older men and postmenopausal women was associated with ameliorated carotid artery compliance to levels observed in age-matched endurance exercise-trained adults.[4, 5] Finally, both moderate or higher intensity aerobic exercise demonstrated similar favorable effects on carotid artery compliance in postmenopausal women who trained at the same level of exercise volume (ie, intensity × duration).
Differential Effects of Physical Exercise on Vascular Hemodynamics
Although the exact role of resistance exercise on vascular hemodynamics, at least in the long-term is not well-defined, it should be pointed out that resistance training preserves the overall strength and functional capacity with aging. The importance of endurance training on vascular health has been initially shown in the Baltimore Longitudinal Study of Aging, suggesting better hemodynamics (ie, pulse wave velocity, augmentation index, and systolic blood pressure [BP]) in older male endurance athletes compared with their sedentary counterparts. A recent meta-analysis of 8 randomized controlled trials evaluated the effect of resistance training on arterial stiffness. There was an age-dependent association of resistance exercise on the outcome, since younger trained participants exhibited an increase in stiffness by 14.3% compared with controls, a finding not reproduced in middle age. Although high-intensity resistance training was significantly associated with an increase in stiffness by 11.6%, moderate-intensity resistance training showed no such association. This latter finding is in line with previous evidence suggesting that moderate-intensity resistance training alone does not modify arterial stiffness in healthy young men or postmenopausal women,[10, 11] while higher-intensity resistance training was associated with deterioration of central arterial stiffness in young and middle-aged adults, and this adverse phenomenon is reversed by concomitant aerobic exercise. A further metanalysis reflected favorable effects of both dynamic moderate-intensity and static low-intensity resistance training on BP levels in patients with optimal BP or prehypertension; however, these observations were not reproduced in patients with hypertension.
Aging-associated structural vessel deterioration is reflected in changes of arterial wall composition with elastin derangement, collagen cross-linking, vascular smooth cell hypertrophy, and enhancement of chronic inflammation. By the side of functional age-related adverse vascular changes, endothelial dysfunction, oxidative stress, and sympathetic drive are progressively enhanced, resulting in ever impaired vascular tonicity. In this setting, it has been postulated that physical exercise exerts beneficial effects on the vasculature by minimizing the extent of structural and functional deterioration associated with aging. The effect of 3 months of aerobic exercise on endothelium-dependent dilation was tested in young and older healthy men, either sedentary or previously endurance-trained. In this latter study, forearm blood flow at baseline was significantly higher in young sedentary adults compared with their older counterparts, whereas, previously, endurance-trained participants of different age demonstrated the same level of forearm blood flow in response to acetylcholine infusion. Finally, the intervention with aerobic exercise in the whole cohort was associated with significant amelioration of endothelium-dependent vasodilation, possibly a result of enhanced nitric oxide bioavailability and reduced oxidative stress.[16-18] These findings observed in men have not been examined in women, whereas there is evidence that postmenopausal women may acutely benefit in terms of endothelium-dependent vasodilation after a single session of aerobic training. A step further, moderate-intensity resistance exercise training alone did not associate with better flow-mediated dilation in previously sedentary postmenopausal women without comorbidities during a period of 18 weeks.
Combined Exercise Training in Women: New Evidence
In the present issue of The Journal of Clinical Hypertension, Corrick and colleagues assessed the effect of combined (ie, aerobic and resistance) exercise training on vascular hemodynamics in previously sedentary healthy women 60 years and older during a period of 16 weeks. Three combined exercise groups were implemented with aerobic and strength sessions being performed in nonconsecutive days with an increasing frequency from 1 to 3 times every single week. The variable of interest for block randomization among the 3 groups was the race, while the adherence to training and weight control during follow-up was reported almost optimal for all participants. Aerobic training with bike ergometer and treadmill exercise was gradually intensified from the first to the eighth week targeting at 80% of the age-predicted maximum heart rate for 40 minutes. The intensity of resistance training was gradually increased to 80% of the maximum weight the patient could lift at one time, with appropriate increasing adjustments over time. Prior to and after 16 weeks of combined training, the 3 groups of women underwent arterial elasticity measurements with radial pulse wave analysis and BP measurements at rest and low/intermediate exercise intensity during a submaximal walk test. Additionally, Corrick and colleagues, before and after the combined training intervention, determined the changes in maximum oxygen uptake and body composition (ie, total fat and lean mass). At least once-weekly aerobic and resistance exercise training was accompanied by lower systolic and diastolic BP at end follow-up as compared with the pre-training BP levels, whereas the increasing volume of combined exercise did not determine the overall hemodynamic load in a dose-dependent manner. Another important finding highlighted in the present study was the significant association of the changes of total vascular impedance with the changes in systolic BP, as well as the changes of systemic vascular resistance with the changes in diastolic BP after adjustment for changes in free-fat mass and free mass. However, no significant differences were observed for large and small arterial elasticity or for total vascular impedance and systemic vascular resistance before and after the combined training.
The novelty of the study is the comparative evaluation of 3 different volume regimens of combined training in older healthy women and that the lower volume training equally contributes to amelioration of hemodynamic load as compared with the higher volume. Moreover, higher volume of combined training with aerobic and resistance sessions performed on alternative days results in resting BP, exercise BP, and heart rate lowering over a period of 3 months, suggesting that even intense resistance exercise when combined with intense aerobic sessions may be not detrimental for cardiovascular hemodynamics.
Although the study by Corrick and colleagues provides novel insights, there are some noteworthy issues related to the study design and interpretation of the results. First, the authors preliminarily excluded patients with diabetes mellitus and smoking given that these two factors interfere with vascular hemodynamics and aging. However, additional comorbidities might have been excluded such as sleep apnea and hyperlipidemia, because both impact negatively on the investigated outcome. Second, block randomization took into account only the race and not body size. More specifically, women with lower body weight and body fat were randomized in the group of higher training volume. Whether participants with higher body adiposity would have been able to adhere at higher volumes of training compared with their relatively leaner counterparts, and more importantly whether baseline body mass index would had a significant influence on BP, remains an undetermined issue. A recent study investigated the effect of moderate-intensity resistance, aerobic, or combined exercise on BP and arterial stiffness in middle-aged overweight and obese adults who exercised 5 days per week for 12 weeks, with no significant changes in vascular hemodynamics compared with a control group who did not exercise for this period. It might be that in that enhanced adiposity cohort, the effects of exercise could not be evident during this limited period of follow-up. Third, in the study by Corrick and colleagues, additional measures estimating vascular hemodynamics such as pulse wave velocity and augmentation index would have provided a more integrated view of the investigated outcome. Fourth, no mechanistic insight for the effect of combined exercise on vascular hemodynamics was reported, since no indirect indices of sympathetic or parasympathetic activation were examined before and after the training intervention. For future studies, proposed simple methods—although not free of limitations—to evaluate sympathetic activity might be mental stress and cold pressor test,[24, 25] as well as the response of diastolic BP from lying to standing. A simple measure to test the changes in training-mediated parasympathetic activity would be heart rate recovery during a treadmill stress test. Moreover, it would be interesting to know the differences in oxidative stress measures or even the differences in nitric oxide bioavailability among the trained groups at different combined exercise volumes and finally to define the aspects of long-term BP variability in the same setting.[28, 29]
Beyond and over the previously mentioned comments, the study by Corrick and associates reopens the debate as to whether high-intensity resistance training when combined with aerobic exercise sessions might be beneficial for vascular hemodynamics in older or even middle-aged healthy patients. The finding that postmenopausal women benefit the same with low-volume exercise compared with women who train more systematically, might be crucial for future prevention strategies and should be confirmed in further investigations. Additionally, it is of clinical priority to assess the more efficient exercise program of combined training associated with higher BP reduction, possibly by implementing a static (isometric) instead of dynamic resistance training, paired with appropriate aerobic exercise sessions. Finally, we should address whether combined exercise training programs of unequal volume (eg, high aerobic and low resistance) compared with programs of equal resistance and aerobic exercise volume, are accompanied with a more pronounced decrease in BP, to further refine the effectiveness of preventive BP-lowering strategies.