Post #1163: Returning to the gym

Posted on June 23, 2021


I used to know what exercise was.  If I wasn’t out of breath and sweating, that wasn’t really exercise.

I completely lost sight of that in the pandemic.  As I aged another year and got ever fatter, I found myself counting more and more things as “mild exercise”.  Puttering around the garden, walking around the block, taking a bit of a bike ride, and so on.  Medically speaking, that’s all exercise. 

Yesterday I found out just how badly I was kidding myself. 

My wife and I went back to the gym for the first time in well over a year.  I don’t know if this event is of interest to anyone, but in this post, I’m going to walk through the odds, the logic, and the experience of getting back into the gym.

The odds in brief:  I figure that at our current community rate of COVID-19 incidence (1.6 new cases / 100,000/ day), going to our gym every other day, in a room with an average of 30 people, we’d end up sharing gym space with a COVID-19 infected individual about once per year.  But the likelihood that we’d end up spending considerable time close to an infected individual — the sort of situation that can easily lead to transmission of disease — works out to about once per 15 years.  And the likelihood that we’d end up in the same room as an infected “super-emitter” of COVID-19 — another situation that can easily lead to spread of infection — is also about once per 15 years.

The long and the short of it is that for me — fully vaccinated, age 62, and fat — the positive health impact of going to the gym vastly outweighs the COVID-19 risk at present.   Easily a 100-to-1 ratio of benefit to cost.  As with the average American, I’m far more likely to die from slowly degenerative diseases than from anything as swift and dramatic as COVID-19.

The odds

If you read this blog, you know that I’m quite cautious about getting exposed to COVID-19.   For example, I’ve been wearing N95 masks for the duration of the pandemic.  I also like to keep tabs on what my odds are, in terms of risk of infection.

Mid-pandemic, working out in a gym was considered a middle-of-the-road activity in terms of risk of COVID-19 infection.  You can see my summary of several qualitative rankings of activities back in Post #811: Qualitative rankings of activities by risk of COVID-19 infection.  Some experts said it was comparable in risk to indoor dining or going to a hair salon, others placed it as being no more risky than grocery shopping.  All experts appeared to agree that it was less risky than going to a bar or attending church services.

The first question I needed to answer was:  What’s the likelihood we’d be sharing gym space with an individual with an active COVID-19 infection?  That’s the first step toward the ultimate question, which is, how likely are we to pick up a COVID-19 infection at the gym? 

I’ve done a similar calculation several times before, going back to at least Post #680.  The gist of it is that you need to know:

  • New infections per day in your area (hard data).
  • A guess as to how many unreported cases occur for every reported case.
  • A guess as to how many days the average person remains infectious.

The product of those three tells you the likelihood that any one individual you meet is infectious.  Multiply by the number of people you are likely to meet, and that tells you the likelihood that you’ll cross paths with an infectious individual.

For my situation, those numbers and guesses are:

  • 1.6 COVID-19 infections / 100,000 residents / day.
  • 2 undiagnosed cases for every diagnosed case
  • 4 days (averaging both symptomatic and asymptomatic individuals).

With those numbers, I estimate that any randomly-selected Virginia resident has a 0.019% chance of being infectious.  That works out to about one person in every 5000.

In the gym we go to, all the weight and cardio equipment that we use is in one large, high-ceiling room.  We looked over our gym on Monday to get sense of how many people would likely be in that room at one time.  Best guess, under current conditions, at the time we’re likely to go, including turnover of the population during the time we’d be there, we’d be sharing that large room with about 30 people. 

And so, all other things equal, the likelihood that we’d end up sharing gym space with an infectious individual is 30 x 0.019% = 0.6%.  Or, stated differently, one out of every 172 trips to the gym, we’d be in the same room as someone who was actively infectious with COVID-19.  Given that we tend to go roughly every other day, at current incidence, about once per year, we’d be sharing gym space with someone with an active COVID-19 infection.

You need to take any such number with a large grain of salt.  Mainly, we don’t know how the average gym-goer compares to the average Virginia resident.  (FWIW, users of this facility skew elderly.)  My guess is that between the age and the health-consciousness, we’re looking at a fairly cautious, mostly-fully-vaccinated population.  But in addition, we can’t readily factor in the impact of heavy breathing during exercise, which increases emission of aerosol droplets.

But in addition, you need to figure that we’d spend very little time next to any one individual.  Based on the best epidemiological evidence, it takes something like 15 minutes’ close exposure to an infected individual to generate an appreciable risk of infection.  The only time that would occur would be side-by-side use of cardio equipment.  That means I risk intense exposure to (typically) just two persons in any one visit — the people using the cardio machines on either side of me — not 30.  That means that I’m likely to get an intense exposure to an infected individual just (2/30) 1/15th as often.  In other words, I risk an exposure time long enough to generate an infection in just one trip in every 15 years. 

Finally, you have to worry about infected super-emitters.  Best evidence says that about 6.7% of all individuals are “super-emitters” of aerosols.  These individuals are capable of filling a large space with aerosols, and so present a hazard from a distance.  That too works out to be about one-in-fifteen.  So, I risk a less-well-defined exposure to an infected super-emitter about one trip in every fifteen years.

Health benefits and the cost/benefit calculation

The other side of the cost-benefit analysis involves the health benefits of exercise.  Near as I can tell, any estimate of that is nebulous at best.  (I’m not dismissing the fact of benefits, I’m just saying that it’s a hard thing to estimate from non-experimental (observational) data).

I guess if I’m going to cite pro-exercise propaganda, it might as well come from socialized medicine.  According the the British National Health Service, regular exercise results in:

  • up to a 35% lower risk of coronary heart disease and stroke
  • up to a 50% lower risk of type 2 diabetes
  • up to a 50% lower risk of colon cancer
  • up to a 20% lower risk of breast cancer
  • a 30% lower risk of early death
  • up to an 83% lower risk of osteoarthritis
  • up to a 68% lower risk of hip fracture
  • a 30% lower risk of falls (among older adults)
  • up to a 30% lower risk of depression
  • up to a 30% lower risk of dementia

YMMV.  Note all of the “up to” phrasing.  You’ll find the same list, absent the numbers, if you look at the U.S. CDC.

The actual benefit is not this full amount.  It is only the marginal benefit of returning to the gym now, as opposed to six months from now.   How can I get some handle on that?

The easy and direct way to sum all of this up is a simple risk-of-death calculation.  In the U.S., the average 62-year-old man has a 1.3% annual risk of death (from the U.S. Social Security Administration.)  For the sake of argument, assume exercise cuts that by 30% as stated above.  That’s a 0.4% reduction in risk-of-death this year, from returning to the gym this year.

How does that compare to increased risk-of-death from COVID-19 exposure at the gym?  Over the course of the year, I estimated two ways I could have a one-in-fifteen chance of some potentially infectious exposure to COVID-19.  (Cardio next to an infected individual, or being in the same room as an infected super-emitter of aerosols).  But I’m vaccinated, so my risk of actually getting infected, given an exposure that would infect an un-vaccinated individual, is just 5% of that.  And then, risk of death, among COVID-vaccined COVID-infected individuals appears to be about 2% (per the U.S. CDC), but the median age at death is 82.  (So, in all likelihood, what you’re seeing does not reflect the actual mortality rate of the typical vaccinated individual with a breakthrough infection).  I am guessing that, for a person my age, the relevant rate would be about 0.2%.  When I run all that through the meat grinder (2 * 1/15 * 0.05 * 0.002), I end up with a 0.0014% annual chance of dying from COVID-19 as a result of returning to the gym under current conditions.

And so, near as I can tell, based on this simple risk-of-death calculation, I’m coming well ahead by returning to the gym early.  There’s a noticeable 0.4% reduction in annual risk of all-causes mortality from doing so, weighed against a negligible 0.0014% increase in risk of death from COVID-19.  Benefits outweigh risks by more than 100-to-1.

Behavioral aspects

The final piece of this is behavioral.  Fact is, I just won’t get regular intense exercise unless I go to the gym.  Absent that, it’s the occasional stint on the home elliptical exerciser, and the occasional bike ride.  The every-other-day session of weightlifting and intense cardio just will not happen if I don’t go to the gym.  I can’t say why that’s true, but I can say that it’s true.

That first return trip is hard to do.  There’s just a big psychological barrier.  You’ve trained yourself to look at some activity as risky.  You tend to treat the risks of those activities as black-and-white:  Either it’s OK to do something, or it’s not.  And for a long time, going to the gym was Not OK.  So this is akin to breaking a long-standing taboo.  Rational thought only takes you so far.

But in fact, rationally, it’s all about the odds.  Things change.  Between reduced incidence in the community, and vaccination, the risk of serious health consequences from most public activities are now vastly lower than they were half-a-year ago.

For something with a clear benefit, those formerly risky activities are now worth doing again.  But I find that my behavior is “sticky” with regard to many things that were off-limits during the pandemic.  E.g., I still haven’t gotten a professional haircut since the start of the pandemic.  There, the benefits don’t seem worth the risks.  And I still wear a mask when grocery shopping, ditto.  I don’t see any particular benefit to grocery shopping maskless as opposed to masked, and there is still some (very small) risk of COVID-19 infection.

As a family, we’re slowly returning to our normal pre-pandemic patterns.  We’ve gone to the movies, done some outdoor restaurant dining, and so on.  But at this point, I’m still not sure I’m ever going to feel totally normal in a large crowd, in a crowded indoor space, or in close proximity to strangers.  Maybe that’ll happen eventually.  For now it’s one treadmill step at a time.