Is Too Much Exercise Harmful?

Is there such a thing as too much of a good thing?

The WHO recommends that most adults do at least 150 minutes of moderate to vigorous activity per week¹.

This is in addition to the two strength training sessions.

Everyone always forgets about the resistance training part.

This is the minimum recommended activity level.

Some data suggests that doing 3 to 4 times the aerobic amount may actually be more beneficial².

Photo by Brian Erickson on Unsplash

The question then becomes, for a small number of people:

Is exercising too much harmful?

The generally accepted answer to this question is yes.

But as always, the answer is it depends.

The datasets we use to make these inferences are not exactly perfect.

The idea that too much exercise is harmful is known as the “Extreme Exercise Hypothesis”.

This theory suggests a U-shaped curve in terms of exercise benefits, with significant benefits at low to moderate levels of exercise, but at extreme levels, there may be a signal of harm³.

Exercise at the extremes: the amount of exercise to reduce cardiovascular events. J Am Coll Cardiol. 2016

In terms of potential harms of extreme levels of exercise, there is evidence to suggest worse cardiovascular health metrics, including more:

• Coronary artery calcification

• Atrial fibrillation

• Myocardial fibrosis

• Sudden cardiac death

At face value, this does not paint a rosy picture for large volumes of weekly exercise.

Out of these four issues listed, it appears that the increased risk of atrial fibrillation is the most likely related to extreme levels of exercise⁴.

The issue of harm from too much exercise is far from settled, and I do not expect this to be the last word here. Some researchers have made this their life’s work and have far more to say than I do.

But I would make some observations.

When evaluating the extreme exercise hypothesis, most trials use questionnaires and ask participants, “How much do they exercise?”.

These questionnaires are often unreliable, and even when the participants are tracked, they are only tracked for short periods.

Rather than asking someone how much they exercise, you can evaluate how aerobically fit they are. In general, more exercise equates to higher levels of fitness. Very high levels of exercise are required to achieve the highest fitness levels.

When this approach is taken, there is a monotonic reduction in risk from the lowest levels of fitness to the highest⁵.

Mortality Risk for the Entire Cohort According to Peak METs Achieved. J Am Coll Cardiol. 2022

This finding runs against the thesis that too much exercise is bad for you, or even if it does cause specific issues later in life; they are unlikely to be very consequential.

However, the key point for me is when you look at the statistics involved in some of these analyses.

Let’s look at one of the most commonly quoted studies suggesting that extreme levels of exercise are harmful⁶.

Hazard Ratios (HRs) and 95% CIs for Leisure Time Moderate- to Vigorous-Intensity Physical Activity and Mortality.

From the graph above, you can see that the mortality reduction begins to go back up at the highest levels of exercise. This finding is what we often see in these studies.

The issue, however, is that the amount of people in this group is relatively small, and the error bars for this data point (The Lines with the T shape above and below the data point) are large and overlap with the ones prior to it. This suggests that there may be no difference between these later two groups.

This is a statistical point which most researchers would quickly point out, but if examining scientific data is not something you do regularly, this is likely to pass you by.

Regardless of this point, there is a more important factor at play.

The highest level exercise group is categorised by doing more than 75 MET hours per week. This is the equivalent of doing more than ten times the WHO recommendation of 150 minutes per week. This is a huge amount of weekly activity that typically only ultra-endurance athletes will only achieve.

For most people, this will not be an issue.

I wanted to cover this topic not to provide the definitive answer to the extreme-level exercise hypothesis but to highlight that for most people, this question is not even relevant.

Many people getting into exercise for the first time often bring up this issue.

For someone doing absolutely no regular exercise, the likelihood of you falling foul of this issue in the near term is exceptionally low.

If it does happen to you. I want an invite to your book launch.

If you are one of those rarified individuals who do such levels of exercise, there is certainly a signal of harm but from datasets that are not the most reliable.

The main point everyone should take away is that the greatest benefits in risk reduction happen when someone moves out of the lowest fitness category.

This is where the biggest bang for buck occurs⁷.

The benefits of going from high fitness to extreme fitness levels will likely be debated for some time to come, however.

1. https://www.who.int/news-room/fact-sheets/detail/physical-activity

2. Eijsvogels TM, Molossi S, Lee DC, et al. Exercise at the extremes: the amount of exercise to reduce cardiovascular events. J Am Coll Cardiol. 2016;67:316–29.

3. The "Extreme Exercise Hypothesis": Recent Findings and Cardiovascular Health Implications. Curr Treat Options Cardiovasc Med. 2018 Aug 28;20(10):84.

4. Recent Findings and Cardiovascular Health Implications. Curr Treat Options Cardiovasc Med. 2018 Aug 28;20(10):84.

5. Cardiorespiratory Fitness and Mortality Risk Across the Spectra of Age, Race, and Sex. J Am Coll Cardiol. 2022 Aug 9;80(6):598-609.

6. Leisure Time Physical Activity and Mortality: A Detailed Pooled Analysis of the Dose-Response Relationship. JAMA Intern Med. 2015;175(6):959–967.

7. Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Netw Open. 2018;1(6):e183605.