When I was a younger trainer the only things that mattered for me as an individual in the gym as well as in my program design for clients was developing strength, adding muscle and burning off body fat. Two and a half decades later those are still the primary things that clients are interested in focusing on and what I spend most of my time helping people address, however as I embrace middle age other important aspects of health and fitness are becoming more of a concern. For myself and for my clients.
I was always a strength oriented athlete, and I use the words strength and athlete loosely. I was neither particularly skilled athletically or strong until I found the gym. In the weight room I found an environment where I was able to excel and use my particular build to great advantage. If something involved moving heavy weights I was all over it. Aerobically oriented sports were never my forte. I recognized the importance of cardiovascular fitness and programmed those components for my clients but it was never the focus. Without question the only ones who did their cardio were those who were excessively focused on body composition and burning calories.
These days I find myself thinking about the risks of heart disease, the decreases in athletic performance and the capacity to perform everyday physical activities that clients are encountering. How to maximize risk reduction for diabetes, cancer, stroke and a myriad of other life limiting conditions. More than ever I wish my clients would make time to exercise, specifically aerobic exercise that trains their cardiovascular systems. Recently I came across an outstanding study that not only reinforced my concerns about this topic but also demonstrated the impact that regular, consistent aerobic exercise has on significantly reducing the impact of aging and a sedentary lifestyle. One of the most important pieces of the study is the amount of exercise that is necessary to achieve what literally are time reversing impacts on our hearts.
Put Some Heart In It
Our left ventricle is responsible for pumping oxygenated blood to the rest of the body. In a healthy heart, as blood fills the left ventricle it increases the stretch on the muscle tissue that forms the ventricle. This stretch on the muscle tissue results in a stronger contraction. If an increased amount of blood is pumped into the left ventricle the stretch on the muscle tissue is even greater and the resulting contraction is greater. This means even more blood is pumped from the heart to the rest of the body. We refer to the amount of blood that is pumped from the heart with each beat as the stroke volume. Being able to increase the stroke volume, pump more blood, during activity is generally a good thing.
If less blood fills the left ventricle there is less stretch on the muscle tissue and the result is a weaker contraction. This means less blood is then pumped from the heart, a lower stroke volume. So anything that causes less blood to fill the left ventricle between each beat or reduces the force with which the ventricle contracts is detrimental.
Now for the bad news, as we age the left ventricle tends to get stiffer. This results in a decrease in the amount of blood that can fit in the chamber. This is a problem because it means there is less blood available to be pumped out. The reduced amount of blood also places less stretch on the muscle tissue resulting in a weaker contraction. As we just learned these two things result in a lower stroke volume.
Not only do we see a reduction in stretch on the muscle tissue because of the reduced amount of blood in the ventricle, we also see a reduction in stretch on the muscle tissue because the muscles themselves have become stiffer and thicker. Unlike skeletal muscles where thicker means stronger, with cardiac muscle tissue thicker does not necessarily always mean better. So essentially there are now three factors resulting in a lower stroke volume; less blood filling the chamber and available to pump out, less stretch on the muscle tissues because of the reduced amount of blood resulting in a weaker contraction and less stretch on the heart muscle because it has become stiffer and thicker. In a nutshell, aging sucks for our hearts, far more so if you are sedentary.
By the time someone reaches their senior years (65+) if they have been sedentary, adding in moderate aerobic exercise is not very effective in reversing the stiffness that is found in the left ventricle (Don’t stop exercising seniors. Exercise is still effective through other mechanisms). By contrast, masters athletes that have engaged in a lifetime of physical activity tend to show hearts that appear and function as they would in much younger individuals (Arbab-Zadeh et al 2004). While it might not be reasonable to expect everyone to exercise at the same volume and intensity of competitive athletes, 4-5 days a week of regular exercise over a lifetime does appear to provide most of the benefits (Bhella et al. 2014).
Researchers have determined that this stiffening process begins in and can be identified in middle age (Fujimoto et al. 2012). This led researches to question if they could provide an intervention in sedentary middle age individuals that would stop, limit or reverse the negative changes seen in the heart.
The Study Details
Howden et al. (2018) theorized that if they took a group of sedentary middle-aged individuals and put them on an exercise program performed 4-5 days a week consisting of cardiovascular exercise performed for at least 30 minutes, including 1-2 high intensity interval training sessions, they could prevent left ventricular stiffening.
There are four main reasons we should consider this a higher quality piece of research. First, it was a prospective study. Subjects were put on an intervention and then the results were measured instead of the majority of similar research that is retrospective in nature, meaning they take a current population and look back at what they report they did in the past and try to determine to what extent their prior behavior contributed to their current status. Secondly the study also included a parallel control group whose activity was supervised and their results directly compared to the intervention group. Third, the study was randomized. Once subjects were determined to be eligible for the study they were randomly assigned to either the intervention group or the control group. Fourth, the study lasted for two years. Prospective studies are very complicated to conduct and most similar types of research in this area are of much shorter duration. Usually to have a longer term measurement of cardiovascular impacts retrospective studies are performed. In addition, throughout the entire two years the variables in question were controlled in both groups
Ultimately sixty-one healthy middle-aged (45-64 years) individuals were chosen. Anyone who reported a history of regular exercise was excluded. Fifty-two subjects completed the study, 28 in the exercise group and 24 in the control group. These numbers were determined to be large enough to make the results of the research statistically significant. The subjects in the experimental group had a slow ramp up of their exercise volumes and intensities. For the first month of the study the subjects in the experimental group performed three 30 minute cardio sessions per week at a base rate that was 1-20 beats below their maximum steady state heart rate. In the second month 2 sessions were added where the subjects trained at their maximum steady state. In month three a third session at maximum steady state was added. In month 3 the subjects also began to perform high intensity intervals at 90-95% of their peak heart rate. They performed a 4 minute interval followed by 3 minutes of recovery at 60-75% of peak heart rate. Four rounds of the intervals were performed. The day following high intensity intervals the subjects had a recovery day where they did 20-30 minutes of walking or light aerobic activity.
By month 6 the experimental group was training 5-6 days per week which included 2 interval sessions, 1 long training sessions of at least an hour and one 30 minute session at their base pace. This program was maintained for 4 months. At this point, after 10 months subjects were retested to adjust their training zones and they began a 14 month maintenance phase. In this phase they only performed intervals 1 time per week. The subjects were allowed to utilize different pieces of exercise equipment (bike, treadmill, elliptical, rower) or exercise outdoors (running, cycling, swimming) and were encouraged to perform different types of exercise to make the sessions fun and avoid injuries. They were also instructed to perform strength training 2 times per week.
The control group was instructed to perform yoga, balance and strength training 3 times per week for the entire 2 years. They were not allowed to perform any endurance exercise. Both groups were closely monitored throughout the entire 2 years.
Over the course of the first 10 months of the study the experimental group saw their maximum oxygen uptake (VO2max) increase by 18%. This increase was then maintained over the following 14 months of the maintenance phase. The control group actually saw their VO2max decrease by 1% over the course of two years as would be expected in untrained individuals as they get older.
Left ventricular end-diastolic volume (LVEDV) is a measure of the amount of blood that is in the left ventricle when it finishes its relaxation phase, right before it contracts. More blood in the chamber means the surrounding heart muscle tissue is more pliable, stretching more to allow the increased volume. This signifies a less stiff left ventricle and will result in higher stroke volumes because more blood is available to be pumped. The experimental group saw a 17% increase in LVEDV over the initial 10 months of training.
Other direct measures of stiffness and pressure-volume relationships all showed a marked improvement in the experimental group. The experimental group also saw a five beat drop in their resting heart rate while the control group did not experience any change.
Putting It All Together
The primary take away from this study is that 2 years of exercise for 30 minutes, 4 to 5 days a week including at least 1 day of higher intensity interval training results in significant reductions in left ventricle and overall myocardial stiffness. This can be directly related to decreases in the risks of cardiovascular disease. This exercise protocol is exceptionally similar to recommendations offered by the American Heart Association and The American College of Sports Medicine. Both promote 150 minutes of moderate exercise per week performed over 5 days per week for 30 minutes per day or vigorous exercise performed 3 days per week for at least 25 minutes.
The combination of low, moderate and high-intensity exercise also showed marked improvements in measures of fitness (VO2max and resting heart rate) that are also correlated with decreased cardiovascular risk. The authors theorize that the higher intensity component of the program is a particularly powerful driver of the changes seen in these fitness related measures.
For those readers who have been riding their desk and sofa for far too long, the study also showed that these changes can take place in sedentary middle aged individuals and that this population does have the psychological capacity to adhere to a long term, regular exercise program. If you haven’t been a lifelong athlete or regular exerciser there is now evidence that as an average middle-aged individual you can significantly improve the condition of your heart, lower your risk of heart disease and death and achieve higher levels of fitness.
Arbab-Zadeh, A., Dijk, E., Prasad, A., Fu, Q., Torres, P., Zhang, R., Thomas, J.D., Palmer, D. and Levine, B. (2004) Effect of Aging and Physical Activity on Left Ventricular Compliance, Circulation, Sep:110(13): 1799-1805
Bhella, P., Hastings, J., Fujimoto, N., Shibata, S., Carrick-Ranson, G., Adams-Huet, B. and Levine, B. (2014) Impact of Lifelong Exercise “Dose” on Left Ventricular Compliance and Distensibility. J Am Coll Cardiol. Sep 23: 64(12): 1257-1266
Fujimoto, N., Hastings, J., Bhella, P., Shibata, S., Gandhi, N., Carrick-Ranson, G., Palmer, D. and Levine, B. (2012) Effect of ageing on left ventricular compliance and distensibility in healthy sedentary humans. J Physiol. Apr 15: 590(pt 8): 1871-1880.
Howden, E., Sarma, S., Lawley, J., Opondo, M., Cornwell, W., Stoller, D., Urey, M., Adams-Huet, B. and Levine, B. (2018) Reversing the Cardiac Effects of Sedentary Aging in Middle Age-A Randomized Controlled Trial. Circulation. 117.030617. doi: 10.1161/CIRCULATIONAHA.117.030617. [Epub ahead of print]