In the quest to improve body composition, it’s easy to forget that exercise has other health benefits. With heart disease being the number one cause of death in both men and women, anything we can do to lower our risk for this often “silent” health problem is favorable. Research clearly shows physical activity, especially aerobic exercise, reduces risk factors for heart disease. Most doctors tell patients to do moderate-intensity exercise like walking to lower their risk for heart disease, but is vigorous training like high-intensity exercise a better choice?
The Heart Healthy Benefits of Exercise
Exercise positively impacts heart health in a number of ways. For one, it improves the physical function of your heart. With regular aerobic training, the stroke volume of your heart increases. As a result, your heart becomes more efficient at pumping blood to the tissues that need it during exercise and at rest. In addition, exercise improves blood vessel function by helping arteries open up more easily to deliver blood and oxygen to hungry muscles and tissues.
Exercise also reduces the number of risk factors linked with a greater risk for heart disease. It does this by raising HDL cholesterol, reducing blood pressure, improving insulin sensitivity and by lowering body weight. Plus, exercise helps reduce stress, a factor that may contribute to heart disease. Research shows men and women with the highest levels of physical activity have a 20 to 35% lower risk for dying of cardiovascular disease and from all causes. Sounds like a good reason to exercise, doesn’t it?
Moderate versus High-Intensity Exercise: Is One More Heart-Healthy Than the Other?
When a group of researchers in 2006 reviewed epidemiologic studies in which participants exercised at different intensities, they found a pattern. All of the studies showed greater cardiovascular benefits from high-intensity exercise relative to exercise of moderate intensity. This was true even when researchers controlled for total energy expenditure.
Another study published in the Journal of the American Medical Association found the risk of heart disease dropped by 4% with every 1-MET increase in exercise intensity, irrespective of exercise volume. The association held even when factors like BMI and diet were taken into account. Physical activity, in general, has benefits but vigorous exercise may offer greater cardiovascular benefits than moderate-intensity workouts. One study showed walking at a moderate pace only minimally reduced coronary artery disease risk, regardless of frequency or duration.
Interestingly, the JAMA study showed resistance training also lowers risk for cardiovascular disease. How so? Previous studies show resistance training improves insulin sensitivity and lowers the risk for metabolic syndrome, a risk factor for coronary artery disease.
Why might high-intensity exercise offer more cardiovascular benefits than moderate-intensity exercise? One theory is high-intensity exercise improves the functioning of the autonomic nervous system. Your autonomic nervous system has two components. One component called the sympathetic nervous system speeds up your heart rate and raises your blood pressure when it’s activated. It’s called the “fight or flight” portion of your nervous system and is brought into play during periods of physical and mental stress. For example, when you see a big black bear coming towards you your sympathetic nervous system goes into overdrive. The parasympathetic division is the “rest, chill and digest” portion of your autonomic nervous system. It slows down your heart rate, reduces your blood pressure and sends blood flow to your digestive organs.
Effects of High-Intensity Exercise on Nervous System Activity
High-intensity exercise may be more effective than moderate-intensity exercise because it creates a healthier balance between the sympathetic and parasympathetic components of your nervous system. It does this by enhancing the activity of the parasympathetic nervous system. A dominant parasympathetic system, where blood pressure and heart rate are lower, is more favorable to cardiovascular and blood vessel health. One way meditation and other stress reduction techniques may lower the risk for heart disease is by increasing parasympathetic nervous system activity relative to the “fight or flight,” sympathetic portion. “Calm” is better when it comes to the health of your heart.
In addition, high-intensity exercise improves aerobic capacity (V02 max) more than moderate-intensity exercise based on several studies. With high-intensity interval training, you can get greater improvements in aerobic capacity and spend less time doing it.
What about People Who Already Have Heart Disease?
Some doctors hesitate to recommend high-intensity exercise to patients who have had a heart attack. According to a study published in the journal Circulation, the risk of a heart attack or other heart-related problem occurring in response to high-intensity exercise is low even among patients undergoing cardio rehab. Another study in patients with heart failure showed vigorous exercise produced greater improvements in cardiovascular fitness in heart failure patients than moderate-intensity exercise did. Of course, people with heart disease or a history of heart disease should follow the advice of their doctor. High-intensity exercise isn’t appropriate for everyone.
Heart Health and Endurance Exercise
One caveat – recent research suggests there is a point of diminishing cardiovascular returns. In fact, athletes who compete in extreme endurance events like ultra-marathons may be putting the health of their heart at risk. Some studies show athletes have higher levels of markers that indicate heart damage in their blood after long periods of extreme exercise. These changes are temporary but some experts believe that over time extreme training could lead to changes in heart structure and a greater risk for abnormal heart rhythms. The take-home message? Train hard but skip the Ironman distance triathlon.
The Bottom Line
High-intensity exercise seems to have an advantage over moderate-intensity workouts when it comes to heart health. Vigorous workouts boost aerobic capacity, possibly to a greater degree than moderate-intensity exercise. Plus, they appear to be more beneficial for reducing the risk of coronary artery disease. Ready for a little HiiT? It’s the most time expedient way to enjoy the cardiovascular benefits high-intensity exercise offers.
References:
J Cardiopulm Rehabil Prev. 2010 Jan-Feb;30(1):2-11. doi: 10.1097/HCR.0b013e3181c56b89.
Circulation. 2003; 107: e2-e5 doi: 10.1161/01.CIR.0000048890.59383.8D.
“Vigorous Versus Moderate-Intensity Exercise” Len Kravitz, Ph.D. (2006)
Harvard Health Publications. “The Link Between Stress and Heart Disease” December 2013.
JAMA Vol. 288. No. 16. October 23/30, 2002.
Circulation. 2000: 102: 975-980.
Med Sci Sports Exerc. 2006 Jul;38(7):1208-15.
Journal of Physiology, 588, 4345-4346. November 15, 2010.
Med Sci Sports Exerc. 2007 Apr;39(4):665-71.
Evid Based Med 2013;18:159-160 doi:10.1136/eb-2012-101093
Sportscience 5(1), sportsci.org/jour/0101/cf.html, 2001. “Effects of High-Intensity Intermittent Training on Endurance Performance”
JCHF. 2013;1(6):514-522. doi:10.1016/j.jchf.2013.08.006.
Circulation.2012; 126: 1436-1440.
Health Hub at Cleveland Clinic. “Can Too Much Extreme Exercise Damage Your Heart?” 9/2014.
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