High Intensity Workouts

Can your exercise routine kill you?

Can your exercise routine kill you? Maybe. But lots of things done poorly can kill you. Water can kill you: 6 liters will kill half the people who drink that much (called the Lethal-Dose 50 or LD50). Like coffee? 120 cups will probably put you under. But what about exercise? Isn’t that supposed to be good for you? It is good for you. At least most kinds of exercise. There is evidence, though, that high intensity exercise can have negative health effects over time if done to extremes. Before the bad, though, let’s focus on the good.

What is high intensity exercise?

High intensity exercise is typically defined as exercise that brings your heart rate up to or close to 85-90% of your maximum rate. There are as many ways to figure your maximum heart rate as there are websites but the standard formula is to subtract your age from 220 and multiply that number by 0.85 to get beats per minute. View that as a good starting point that will change as you exercise more and train your heart and your body. (Go here to Runner’s World for an explanation.) I maintain a heart rate of about 148 beats per minute for a 5k running race and have pushed to over 170 for brief workouts. Done properly and infrequently these workouts exercise your heart, which is made of muscle, expand and scrub your blood vessel walls as blood surges to feed your muscles, and increases your lung’s ability to process oxygen and carbon dioxide.  All good things.

So what’s the downside? The downside comes when people think that if one day is good then two must be better and a whole week will turn me into Superman by next Friday. Once a week or so is good. And depending on your age and fitness level, maybe several times a week is fine. But at some point, prolonged and constant high intensity exercise can have negative benefits. What are they?

High intensity workouts can exacerbate existing conditions

We’ve all heard stories of someone who started running and dropped dead of a heart attack. I knew a family of brothers who lost their youngest sibling from an aneurysm while running. Doctors guessed that the problem was pre-existing and triggered by exertion and that he was dead before he hit the ground. But other, more benign, problems can crop up. Knee and foot problems are common. Muscle soreness can linger and make even walking painful. Pulled muscles and torn ligaments can occur. If you start a regiment that includes high intensity workouts then expect to find any chinks in your armor. This is just the nature of machinery. Slow and easy is usually painless but add some stress and you start finding the weak spots.

High intensity workouts can contribute to poor rest

It seems that you would sleep like a log after these workouts but the opposite is often true. Your body is either too amped up or too sore to rest. Yoga and meditation can help as can baths. An aspirin helps me relax. And poor rest can contribute to a compromised immune system as well.  And make you damned crabby. Who wants that?

This is age and condition dependent but I’ve had to learn to leave lots of room for rest healing. I need just about a full two weeks of easy stuff to recover from a really hard workout.

What is the real killer?

Prolonged high intensity training becomes a problem when your heart begins to deform. Remember that your heart is just a mid-line pump that pushes blood around your body. During times of intense exercise when your cells and muscles scream for every bit of energy, they can get your heart does two things: it starts pumping faster and starts to pump more volume. It’s the volume that can hurt you. At those levels of exercise, the heart expands more to gather up more blood to push. When it expands, the heart muscle, especially on the right side which tends to be smaller, can become thin and stretched just like a balloon will when you blow it up too much. And just like that balloon, it can become weakened and limp when you maintain that pressure. It’s known, too, that very high heart rates can skew your heart’s electrical circuit and develop into arrhythmias or heart rhythm disorders.

What to do?

Don’t be scared: be smart. For most people doing intense workouts once a week or a couple times a month is fine and adds to your health. Your heart will thank you, your lungs will thank you, and your cholesterol will thank you. More than that is fine for short periods. I’ve done a couple cycles of Beachbody Power90 workouts but tone them down a bit and make sure I get plenty of rest if I feel tired.

Remember what you are exercising for. Most people running on the side of the road aren’t Olympic athletes. They run for fun and fitness, and maybe to fit into a new bathing suit. There just isn’t a need to work at such an intense level. For most people, slow and steady is the best road to improved health.

If you want to try it out then start slow and let your body adjust. Ramp it up if you feel good. Slow down if you feel tired. Remember that the whole purpose of exercise is to live better and feel better today. And I recommend stopping after ten cups of coffee.


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