Chronic aerobic exercise reduces the aortic age of an elderly cohort

Central arterial stiffness is a well-established morbidity and mortality marker, particularly in the context of cardiovascular disease (Zieman et al. 2005). Increased arterial stiffness is a physiological aspect of senescence, and is exacerbated by non-communicable diseases such as hypertension, atherosclerosis and diabetes mellitus. Structural alterations in large arterial vessel walls that lead to stiffness include overproduction of collagen, underproduction/breakdown of elastin, medial smooth muscle hypertrophy, increased intimal permeability, migration of monocytes/macrophages, and fibrosis of the adventitia (Zieman et al. 2005). Regular lifelong exercise (i.e. more than 25 years) is a primary preventive strategy known to curtail the rate of arterial stiffening, as described in a recent article in The Journal of Physiology by Shibata et al. (2018). A previous cross-sectional study by Shibata and Levine showed that senior (65+ years) masters athletes have more compliant arteries compared to their sedentary yet healthy counterparts in the control group (Shibata & Levine, 2011). However, the magnitude and duration of exercise that masters athletes participate in is not practical for most. To better understand arterial stiffness in the elderly cohort, Shibata et al. (2018) conducted a cross-sectional exercise study to elucidate whether lower levels of exercise still have similar effects on arterial compliance. Healthy seniors recruited by Shibata et al. (2018) were stratified into four groups based on self-reported exercise levels over at least 20 years: (1) a healthy sedentary group (n = 27) that participated in one exercise session or less per week, (2) a casual group (n = 25) that exercised for two to three sessions per week, (3) a committed group (n = 25) that performed four to five exercise sessions per week (meeting current physical activity recommendations), and (4) a masters group (n = 25) that performed near-daily exercise. Shibata et al. (2018) then measured and calculated multiple surrogate indices to assess both central and peripheral arterial stiffness for each participant. The authors adopted a previously validated mathematical algorithm (Modelflow aortic age) to determine biological aortic age, an index of central arterial stiffness that is independent of blood pressure, calculated from stroke volume (SV) measured using the non-invasive acetylene method, a central blood pressure waveform extrapolated from a finger waveform, and chronological age (Shibata & Levine, 2011). Both Doppler ultrasonography and applanation tonometry (SphygmoCor MX) were used to measure central (carotid–femoral) and upper limb (carotid–radial) pulse wave velocity (PWV), with Doppler ultrasonography additionally used to assess lower limb (femoral–dorsal) PWV. Furthermore, ascending and descending aortic β-stiffness and strain were calculated using aortic cross-sectional areas using thoracic magnetic resonance imaging and brachial cuff blood pressure measurements. Right common carotid β-stiffness index and distensibility coefficient measurements were assessed using carotid pressures derived primarily from brachial applanation tonometry and carotid cross-sectional areas measured with high-resolution ultrasound. Additionally, carotid augmentation index was mathematically derived from radial artery waveform via applanation tonometry, which was then normalized to a heart rate of 75 beats min−1. Finally, total arterial compliance index (TACi), effective arterial elastance index (Eai), and total peripheral resistance index (TPRi) were all calculated with stroke volume index (SVi), which is SV from the acetylene method corrected for participants’ individual body surface area. SVi showed an upward trend with increasing exercise intensity with a significant difference noted between the sedentary and physically active participants. SVi-related measurements showed analogous results: TACi was significantly lower in the committed and masters group and Eai was significantly lower in all exercise groups when compared to control. Additionally, the carotid β-stiffness index and distensibility coefficient were significantly higher and lower, respectively, in the sedentary group than all exercise groups with no significant difference among exercise groups, suggesting that even a casual commitment to exercise over a lifetime has similar cardioprotective effects to lifetime intense exercise. Doppler ultrasonography PWV measurements showed significant reductions in a trend-like fashion across all exercise groups compared to the sedentary group, and calculated aortic age showed a clear declining trend with higher exercise levels; committed and masters cohorts had mean aortic ages that were 11 and 24 years younger than that of the sedentary cohort, respectively (P = 0.066 and P < 0.001). A few subject-related weaknesses became evident in relation to participant recruitment and characteristics. Firstly, Shibata et al. (2018) defined exercise sessions loosely as at least 30 min of aerobic exercise, without strictly defining type, intensity or duration. Previous work by Guimaraes et al. (2010) found that 40 min exercise sessions alternating between 50% and 80% of participants’ reserve heart rate had favourable effects on arterial stiffness, while sessions at a continuous 60% of heart rate reserve had none (Guimaraes et al. 2010). Therefore, the uncontrolled characteristics of exercise in the present study may act as confounding variables. Secondly, researchers intentionally enriched their masters athletes group with top masters contestants (top 10th–15th percentile) of local and regional endurance events, further augmenting the already exceptionally active and healthy group. Thirdly, groups had varying male-to-female (M:F) ratios: the sedentary group had a M:F ratio of 1.25, while that of the committed group was 4. Moreover, out of 102 participants, 100 of them were Caucasian, which is not representative of the general population. Sexand ethnicity-related differences in atherosclerosis and arterial stiffness are well documented in the literature; discrepant M:F ratios between groups and