Exercise: Can You Do Too Much?
Is there a volume of physical activity that is harmful to you?
Is physical activity a part of your routine? Good for you. Regular exercise can strengthen your muscles and improve your endurance. You know that you enhance your cardiovascular system, too. You are likely significantly reducing your risk of a myriad of diseases, including:
- high blood pressure (hypertension)
- heart attack
- common cancers
- poor bone health
- memory problems
- and more.
Physical activity can also enhance your quality of life, improve aging’s physiology, and help you live longer.
Don’t be Pheidippides
Pheidippides served as a Greek messenger. He collapsed and died after running 24 miles across the Plain of Marathon in 490 BC. Don’t be Pheidippides. In all seriousness, can you do too much exercise?
A more modern version of the story emerged from the mind of Robert Browning. His voice is heard in his 1879 poem, Pheidippides:
“So, when Persia was dust, all cried, “To Acropolis!
Run, Pheidippides, one race more! The meed is thy due!
Athens is saved, thank Pan, go shout!” He flung down his shield
Ran like fire once more: and the space ‘twixt the fennel-field
And Athens was stubble again, a field which a fire runs through,
Till in he broke: “Rejoice, we conquer!” Like wine through clay,
Joy in his blood bursting his heart, — the bliss!”
With that in mind, we next turn to the father of aerobics, Dr. Kenneth Cooper.
The aerobics revolution begins
It is 1968. Dr. Kenneth Cooper continues his pioneering work in the exercise realm. He develops a simple means to assess an individual’s oxygen uptake. First, the scientist takes 115 US Air Force male offices and airmen. He evaluates them using a 12-minute field performance test and on a treadmill test of oxygen consumption.
Dr. Cooper found a strong correlation of the field data with the oxygen consumption level in the laboratory. This discovery allowed him to accurately estimate the maximal oxygen consumption from a simple 12-minute performance test.
Training in the aerobic zone
Cooper, the father of aerobics, continues his groundbreaking work, joining other researchers to show:
- Repetitive training in the aerobic zone leads to a significant increase in maximum oxygen uptake and work capacity.
- Men who expended 2000 to 3000 kcal per week had a lower risk (by a relative 36 percent) of a heart attack. Those who did more exercise did not get more risk reduction, but strenuous sports enhanced total energy expenditure. Still, briskly walking roughly 25 miles per week (10,000 steps) or jogging can burn 2000 to 3000 kcal.
You know the rest. Aerobic fitness became the standard for optimal physical activity. Exercise to get your heart rate in the range of 60 to 90 percent of its maximum. Here’s a way to get an approximation of your maximum heart rate:
Calculate your maximum heart rate: Subtract your age from 220. For example, if you’re 45 years old, subtract 45 from 220 to get a maximum heart rate of 175. The maximum heart rate is the average maximum number of times your heart should beat per minute during exercise.
Does aerobic training work? A very kind reader of my writings got me thinking about the benefits of increasing volumes of physical activity. I’ll begin with this critical observation: Aerobic training works, as it:
- increases your capacity for exercise
- reduces your risk of cardiovascular diseases, including heart attack
- drops your risk of a myriad of conditions, including several cancers
“Too much of a good thing can be wonderful!”
These are the provocative words of Mae West. But aerobic exercise is not easy. Getting back to whether you do too much exercise, you will be pleased with the results of one large study from Sweden and the United States.
Researchers followed 660,000 subjects and used the United States exercise guidelines as the minimum recommended volume of physical activity (150 minutes of moderate exercise or 75 minutes of vigorous activity each week). Here are the findings when the scientists compared exercisers with subjects who did no training:
- Those who completed less than the minimum amount had a one-fifth lower risk of dying during the follow-up period of 14 years.
- Those who performed the minimum amount dropped their risk by nearly one-third (a 31 percent relative risk reduction).
- Those who accomplished three to five times the minimum lowered their risk by a relative 39 percent, or well over one-third.
I will not present a comprehensive review of the literature regarding longevity; suffice it to say that no clear answer emerges when it comes to whether you can do too much exercise. Unfortunately, there are remarkably few randomized experiments, so we have no high-level evidence to guide us. Nevertheless, I want to give you some guideposts.
Sudden death during exercise
Let’s start with cardiac events during exercise. You may remember the America runner Jim Fixx, who wrote the 1977 bestseller The Complete Book of Running. He helped initiate the USA fitness revolution by popularizing regular jogging. Fixx died because of a heart attack while jogging at 52 years old.
You may be quite concerned if you are a long-distance runner. Fortunately, such events are remarkably uncommon. A research investigation of nearly 11 million participants of marathons and half-marathons found a cardiac arrest risk of only about 1 in 200,000.
The investigators offered no matched controls; thus, it is difficult to determine if this risk is different from those in the general population. The takeaway message for me is that sudden death events during exercise are remarkably uncommon.
Women without vascular (blood vessel) disease who do moderate or strenuous exercise (as little as once per week) have a lower risk of blood vessel-related events than inactive women. Those who did average to strenuous activity two to three times weekly had modestly reduced risk reduction. Alas, women who did strenuous exercise every day had less protection, at least as compared with those who did moderate-intensity exercise.
Olympic athletes provide a unique opportunity to study the effects of intense physical activity. Former athletes in cycling, rowing, and running at the Olympic Games between 1896 and 1936 had mortality rates not dissimilar to athletes in less challenging (from a cardiovascular perspective) sports such as golf and cricket.
My focus has been on the long-term effects of physical training. But what about overtraining in the short-term? Alas, there is no great measure of how much is too much. Innumerable variables come into play, including your fitness level, body biomechanics, age, cardiovascular wellness, and others. Still, watch for some symptoms that suggest you just may be overtraining. Shape magazine offers some reminders:
- You are at a plateau. Hit the gym too much, and you may have come to a standstill. Your body needs to recover.
- You are gaining weight. Sometimes building muscle adds weight. Other times you may put your body into a state of chronic stress by overtraining.
- Your fitness level is declining. Please don’t break down your muscles without giving them time to repair.
- Your muscles are unusually sore. Okay, your muscles are sore a day or two after working out. But a week later?
- You are short-tempered. While there may be many reasons you feel off, the overtraining syndrome can be one of them. Of course, if you have any concerns, chat with a valued healthcare provider.
- You have a chronic injury.
- Your sleep quality is suboptimal. Usually, if I exercise a lot, I sleep exceptionally well. Overtrain, and your sleep quality may decline. Your cortisol levels are generally lowest just before we sleep, but overtraining can leave these levels too high.
- Your heart is pounding.
- You have not had a menstrual period for at three months or more, but are premenopausal. Not having periods is known as amenorrhea and can lead to a lower bone mass. No periods can increase your chances of injuries such as stress fractures.
- Physical activity offers so many health benefits. But, remember the importance of rest or recovery days. Cheat on your breaks, and you may not be able to achieve your fitness goals. I try to incorporate one or two days each week of only low-level physical activity. By not overtraining, I reduce my risk of injury.
Thank you for joining me. I hope you have a joy-filled day, perhaps with a bit of physical activity.
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Zwiers R, Zantvoord FWA, Engelaer FM, et al. Mortality in former Olympic athletes: retrospective cohort analysis. BMJ. 2012;345: 19–21.
Armstrong MEG, Green J, Reeves GK, et al. Frequent physical activity may not reduce vascular disease as much as moderate activity. Large prospective study of women in the United Kingdom. Circulation. 2015;131:721–729.
Paffenbarger RS, Wing AL, Hyde RT. Physical activity as an index of heart attack risk in college alumni. Am J Epidemiol. 1978;108:161–175 (p 166).