Know When to Stop:

Healthy Heart Rate & the Dangers of Pushing the Limits

Regular physical activity even at a moderate rate yields tremendous benefits for human body overall and the cardiovascular system in particular. Exercise is associated with reduced risks of developing heart diseases and is capable of reversing some conditions even if a person has previously led a predominantly sedentary lifestyle. If you are a bit of a gym junkie, it's likely that you have your sweet spot of exercise intensity that works best for you. If you are only making your first cautious steps into the iron confines of the gym, but aspire to transform and become a better version of yourself, you’ve probably wondered how hard you should train to reap the maximum benefit.

It is not uncommon to think that the higher your heart rate during physical activity is, the better. It does make sense, since this way the heart is pushed to strengthen, tone, and become more resistant to aging. It is important to know, however, that there is a limit to what is healthy and going above it may have dire consequences.

What Is Normal In a State of Rest?

First, let’s establish what is normal when it comes to heart rate. The healthy range of resting heart rate (RHR) for adults is between 60 and 100 bpm. The closer it is to the bottom threshold, the better condition you are in, and, in fact, a heart rate of less than 60 bpm is an indicator of outstanding fitness and is common among professional athletes.

By contrast, the closer one’s RHR is to 100 bpm, the greater the danger of developing heart diseases. A study of about 7,000 men and women aged 45 to 84 conducted over 9 years has shown that for every increase in RHR of 1 beat per minute there is a 4% greater risk of developing heart failure.

Know Your Heart’s Capacity

When we work out, jog, swim or even take a brisk walk in the park, our heart starts beating faster to be able to cater to the body’s increased need in oxygen. While it is a natural process, it is essential to know at which point you stop gaining benefit from this and start harming yourself. There is a widely-used formula that you are likely to hear if you ask for exercise intensity advice. It goes like this: 220 minus your age, which means that for young adults at the age of 30, the maximum healthy heart rate would be 190 bpm.

Ubiquitous as this formula is, as it is commonly seen on posters in wellness clubs, hospital rooms and has become a staple of heart health advice, it has no documented source and there have been a number of studies that suggest it is far too simplistic to account for all the differences in physiology and health history. A series of exercise tests was conducted over a period of 17 years between 1993 and 2010 that measured maximum heart rates of 19,013 participants, both male and female, aged between 40 and 89 and having no cardio vascular disease. The study showed that for men, the “220-minus-age” formula was predominantly true, whereas for women a more accurate calculation would be 206 minus 88% of a woman’s age.

"It is not uncommon to think that the higher your heart rate during physical activity is, the better. It is important to know, however, that there is a limit to what is healthy and going above it may have dire consequences."

This new distinction is significant because for women it means more enjoyable cardio exercise that doesn’t push them further than what seems achievable leaving them dispirited and disappointed in their apparent lack of athletic prowess. In the long run, this could mean higher levels of sports activity simply because doing sports wouldn’t feel like such an uphill struggle.

Different research conducted in 2001 suggested a universal formula of 208 minus 0.7 times age, which was claimed to be especially accurate with respect to physical activity in older age.

How Far Should You Push Yourself?

Is maximum heart rate what you should aim for while exercising? No. It is generally recommended to stay within 50-70% of your maximum rate when engaging in physical activity of moderate intensity, like walking briskly, dancing, doing housework, or carrying groceries. Doing vigorous activities like running, cycling, aerobics, or any competitive sports would normally raise your heartbeat to 70-85% of its maximum capacity.

It is worth noting that your target heart rate while exercising would also depend on your level of fitness and it is highly recommended to start at the bottom threshold of a target heart rate zone and build up strength and endurance gradually. People with a history of a cardiovascular disease should consult their physician to make sure exercise won't do them more harm than good.

What Happens When You Push Further?

If you exercise at 85-100% of your maximum heart rate regularly, which is what athletes participating in long-distance running, triathlon, or rowing do, the heart develops adaptation mechanisms. In order to accomodate to the need to pump up to 5 times more blood a minute than in the state of rest, the right ventricle and the right atrium of the heart enlarge. Although the heart’s dimensions are restored when it slows into its normal resting heart rate, research suggests that repeated strain of this kind can eventually build up into myocardial scarring, increasing the heart’s wall thickness and mass and reducing the percentage of blood pumped out by the right ventricle. This may make people prone to atrial fibrillation and arrhythmia.

Repeated endurance training over long stretches of time akin to what marathoners expose themselves to is also associated with increased coronary artery calcification and atherosclerotic burden. A scope of studies on groups of marathon runners showed that plaque build-up in their coronary arteries was, in fact, more pronounced than in people of the same age leading sedentary lifestyles.

Blood tests taken immediately after running a marathon have shown that in approximately 50% of athletes there is an increase in cardiac markers typically released when the heart muscle has been damaged. Researches haven’t reached a conclusion as to whether such increases in biomarkers are harmful in any way, or are merely a benign side effect of the cardiovascular system’s effort to adapt to the intensity of exercise. Evidence suggests that peaks in cardiac markers are temporary, and in 72 hours after the race, blood tests usually show results that are almost identical to what they were a week before the race.

In spite of the detrimental impact endurance training can have, it is important to understand that the cases we've described relate to extreme levels of physical activity, which is something an average gym-goer is unlikely to do. Being physically inactive is in most cases more damaging to heart health than pushing it a little too far. The rule of thumb is to keep your heart rate in check while exercising and at rest, avoid overtraining, and be aware of the conditions you exercise in, like temperature, humidity, and sunlight. For older people physical activity is of even greater importance. If done wisely and mindfully, exercise will strengthen all body systems and promote longevity.

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