Exercise Interventions to improve Cardiovascular Health in Aging Populations

A 2017 RCT study I found examined the effects either moderate-intensity continuous training (MICT) compared to high-intensity interval training among alder adults (mean age 64) to determine how different exercise variables improve arterial elasticity since large artery stiffness predisposes older adults to cardiovascular diseases (Kim et al., 2017). Addressing (and preventing) arterial stiffness is a major goal for reducing CVD risk. Previously demonstrated in another study by Martinez et al. (2021) whereby HIIT can be a great time-saving type of exercise to improve blood pressure and VO2max, but the study by Kim et al. investigates the influence on arterial elasticity adaptations to HIIT. The study looked at 8 weeks of training which used an Airdyne bike so both upper and lower extremities were involved.

HIIT protocol was as follows:

·        4 x 4min intervals @ 90% Max Heart Rate Reserve (MHRR) with 3 min active recovery @ 70% (MHR). Total of 16min of intensity and 9 min of active recovery for 19min total.

The MICT protocol was as follows:

·        Isocaloric at 70% MHRR for 47min.

Outcome measures were aortic and common carotid artery compliance. Interestingly, only the MICT group demonstrated significant beneficials changes in both large arteries. After 8 weeks of structured MICT this intervention group had an impressing 30% improvement in carotid artery compliance. However, no changes (i.e. reduction) in resting blood pressures was observed. MICT group also did not improve VO2max, but did improve time to exhaustion on the treadmill ramp test increasing about 2 minutes on average. In contrast, VO2max improved on average from 23 to 26 ml/kg/min in the HIIT group.

What I would like to add to this study and see tested would be combining the two training types (i.e. HIIT 2x/ week and MICT 2x/week) and see if maximal benefits of improving endothelial function, blood pressure, cardiac function, and reduction in arterial stiffness. Since HIIT seems to be better at modulating in a beneficial manner everything but arterial compliance, I would propose that using both training types in older adults will get the best of both worlds.

Studies have noted that HIIT is more effective in improving arterial compliance in younger and middle age (i.e. 50 or younger) populations of both sexes with hypertension (Guimaraes et al., 2010). So, if making recommendation to those populations, we could err on recommending more HIIT type exercise. However, a caveat is these studies of the older and younger populations did not use the same mode of exercise, duration, frequency, or intensity which means we cannot make direct comparisons of HIIT vs MICT in older or younger populations.

For example, the study by Guimaraes et al. (2010) had the HIIT group perform the following regimen:

• 16-week study (compared to 8 weeks)

• 3x/week running intervals (compared to 4x/ week of air dyne bike)

• 3x/week strength training (compared to none)

• 40min of training/ session of 1min intervals @ 80% MHRR with 2min rest @ 60%. Total of 13 min of intensity (compared to 16min at 90% MHRR)

The MICT would perform treadmill exercise:

·        40min @ 60% MHHR (compared to 70% MHHR for 47 min)

It is also known that age-related changes of the autonomic nervous system are responsible for increased vascular tone which can contribute to arterial stiffening. Mechanisms whereby this occurs is via a decrease in the sensitivity of the carotid baroreceptor reflex pathway which lead to increased sympathetic tone by default (Kim et al., 2017). So why does MICT for as little as 8 weeks improve arterial compliance in older, untrained populations? Unlikely reasons would be collagen and elastin physical remodeling of the vascular walls. Instead, more global/ systemic influences are more probable such as improving the sensitivity of the autonomic reflexing like the baroreflex, decreasing sympathetic tone, and increasing nitric oxide bioavailability (Kim et al., 2017). Lastly, reasons why MICT vs HIIT might improve arterial compliance in older populations is simply more volume of time the endothelium of the vessels are exposed to shear stresses.

In conclusion, it appears that for older populations 65+ should consider a mixed weekly cardiovascular exercise routine consisting of both MICT and HIIT to improve cardiac output, VO2max, blood pressure, autonomic nervous system sensitivity, and arterial wall compliance.

References:

Guimarães, G. V., Ciolac, E. G., Carvalho, V. O., D'Avila, V. M., Bortolotto, L. A., & Bocchi, E. A. (2010). Effects of continuous vs. interval exercise training on blood pressure and arterial stiffness in treated hypertension. Hypertension research : official journal of the Japanese Society of Hypertension, 33(6), 627–632. https://doi.org/10.1038/hr.2010.42

Kim, H. K., Hwang, C. L., Yoo, J. K., Hwang, M. H., Handberg, E. M., Petersen, J. W., Nichols, W. W., Sofianos, S., & Christou, D. D. (2017). All-Extremity Exercise Training Improves Arterial Stiffness in Older Adults. Medicine and science in sports and exercise, 49(7), 1404–1411. https://doi.org/10.1249/MSS.0000000000001229

Martinez, M, Kim, J, Shah, A. et al. Exercise-Induced Cardiovascular Adaptations and Approach to Exercise and Cardiovascular Disease: JACC State-of-the-Art Review. JACC. 2021 Oct, 78 (14) 1453–1470. https://doi.org/10.1016/j.jacc.2021.08.003