Part Two: Poor Indoor Air Quality – The Invisible Danger to the Virtual Cyclist

In 30 minutes, my gain cave went from delightful to dangerous. Here's how!

If you know anything about me or spend even a short time in my presence, you are aware that my ‘Gain Cave’ is one of my favorite subjects.  I am proud of the space that I have created and we share a bond that rivals my animate relationships.  

My ‘Gain Cave’ has seen me at my most vulnerable, has been at my side during some of my most significant victories and lowest lows, and is always there when I need it.  Its comfortable and nurturing nature has convinced me that there is no reason why I would ever choose to ride elsewhere.  

I haven’t in several years.  Could it be betraying me?  

After researching Part One of this article series, it was clear I couldn’t deny it any longer.  I had to find out for myself.

My Gain Cave

My Gain Cave is a 16-foot by 8-foot space with 7-foot high ceilings located in the basement of my home. There are no windows but are doors that separate it from the mechanical area of the cellar containing the home’s physical plant.  

What was lurking in this space that I couldn’t see?  I decided to perform a simple experiment to find out. I got my hands on an Air-Quality Detector like I mentioned in the previous post and met my mates for a group ride.

I set out to perform two hours of endurance and tempo-paced training with the DIRT XLR C group.  I planned to vary the conditions to mimic those my riding buddies would encounter while training alongside me.  Here’s how it went.    


The detector I used collected the following data: temperature, humidity, PM 2.5, and CO2.

The Adverse Effects of PM 2.5

PM stands for “particulate matter,” and 2.5 refers to a pollutant that is 2.5 microns or smaller.  PM2.5 is extremely dangerous because they bypass our nose hair, mucus, and other body defenses, passes directly to our lungs, and enters the bloodstream.

2010 study showed that short-term (hours to weeks) exposure to PM 2.5 could cause cardiovascular disease-related mortality and other nonfatal events.  Longer-term (a few years) increases cardiovascular mortality risk and reduces life expectancy by several months to years.

The Adverse Effects of CO2

Exposure to CO2 poses direct risks to human health, including inflammation of the lungs, impaired cognitive performance, kidney and bone problems, and other issues.

Exposure to CO2 can also cause headaches, dizziness, restlessness, a tingling or pins or needles feeling, difficulty breathing, sweating, tiredness, increased heart rate, elevated blood pressure, coma, asphyxia, and convulsions.  

Findings published in the journal Nature Sustainability in 2019 cited evidence that short-term exposure to CO2 levels as low as 1,000ppm can cause adverse health issues, like inflammation and cognitive deficits.      

Long-term exposure to levels over 2,000ppm has a more significant impact and causes kidney calcification and bone demineralization.

The Adverse Effects of High Relative Humidity

2016 study examined the thermoregulatory (ability to control body temperature) and circulatory responses and exercise performance of 11 trained runners during exercise in ~31-degree Celsius heat at varied relative humidity (23, 43, 52, 61, and 71%).  The athletes performed five 60 minute steady-state runs (70% VO2 max) followed immediately by an incremental exercise test to exhaustion.

The time to exhaustion was significantly reduced at 61, and 71% relative humidity and a greater thermoregulatory and circulatory stress were evident during steady-state exercise.  The combined thermoregulatory and circulatory strain further limits the capacity to perform all-out exercise to exhaustion.

With that out of the way, it’s time to get to the laboratory.  I added these three bullet points to my pre-ride anxiety checklist and set off on my impromptu experiment.

  • PM 2.5
  • CO2
  • RH

July 4, 2021, 2-hour Endurance/Tempo Training Session - DIRT XLR Group Ride

My trusty Gain Cave was a bit balmy as I prepared to ride, so I turned on the air conditioner.  After fifteen minutes of easy riding, the humidity had decreased to 54% (from 65%), but the CO2 almost doubled to 1026 (from 601).

Poor indoor air quality in your gym is harmful

For the first hour I added fans to circulate the air and the humidity remained pretty constant.  The CO2 peaked at 1,403 and then decreased a little to around 1,200.  The doors were open to the rest of the basement during this time. 

Check your poor indoor air quality with a monitor

I turned off the air conditioner after an hour but left the fans on, and in the next thirty minutes, the humidity increased to 66%, and the CO2 rose to 1,512.

After riding for 90-minutes, I did it.  I closed the doors.  No outside ventilation, but fans remained.  The effect was dramatic, and the results were staggering.

In the next thirty minutes, the humidity increased to 73%, the temperature rose to 73 degrees F (23C), and the CO2 peaked out at a dizzying 2,855 ppm.

poor indoor air quality is harmful

For my thirty-minute cool-down, I opened the doors and turned on the air conditioner, and the humidity dropped to 56% and CO2 fell to 1,184.

Incidentally, the PM2.5 had remained stable during the ride, except at the end, when it increased to 5.3 ug/m3.  I didn’t mention PM2.5 because the levels remained stable and within acceptable limits, and I don’t know if the increase was significant or an anomaly.

Indoor exercise can cause poor indoor air quality

How did I feel, you ask?

I must admit, I did feel a bit foggy and had difficulty focusing my attention on the group and the other elements of the mini-experiment.  Whether the feeling was due to the air quality, the fact that I had ridden over 2 hours, or dehydration, I don’t know definitively.  I do know that I wouldn’t feel comfortable doing that repeatedly for any amount of time.

My wife mentioned that I looked a bit pale, but didn’t seem very concerned.  She left halfway through the ride and shut the door TIGHT behind herself. 

The short-term effects of elevated CO2 were not my major concern.  I had been doing this every day for a long time before I wised up.  The cumulative effects of chronic elevated CO2 are what I was worried about.  So should you!

Multi-taskers Beware

It did make me think, however, and I took the opportunity to perform another simple experiment.  I placed the monitor in my laundry room and performed a complete washer and dryer cycle.  The PM2.5 rose from 4.54 to 12.4 upon completion of the load, which exceeds the EPA Air Quality Standard threshold of 12 ug/m3.

I wanted to get a reading with the Air Quality Detector placed next to the heating unit in my basement. Not going to happen soon.

Not until around October in my parts.

My Basement Gain Cave Essentials

Fans, Fans, and More Fans

The three 20-inch high-velocity industrial units create a training tornado of sweat-wicking satisfaction.  I use these.

a fan will improve poor indoor air quality
Air conditioner improves poor indoor air quality
Portable Air Conditioner

The 14,000 BTU dual-hose air conditioner and dehumidifier takes clean air from outdoors, sends it through a carbon filter, and vents the exhaust to the outside where it belongs.  I like it because there is no water reservoir to forget to empty.  This is the one I use.

Air Cleaner

The portable air purifier has HEPA filtration, a UVC germicidal lamp, and a toxic gas reduction system.  I purchased this unit several years ago when I felt that my throat was irritated after every ride.  Perhaps this was the first indication that I had an air quality problem.  This is the one I use.

Air purifier improves poor indoor air quality


Suppose the indoor air quality in my training area had deteriorated to dangerous levels in the short time I was riding. In that case, I can only imagine the hidden danger that lurks in the cobweb cluttered corners and dusty confines of yours.  Don’t look at me that way.  I have seen the pictures.

In all seriousness, the air we breathe as our respirations increase while exercising may be doing us more harm than good.  It’s worth a look!  

I contacted the company that manufactures the Air Quality Detector I used and explained my experience and the concern I felt for my fellow virtual cyclists.  They agreed to extend a 10% discount to The Zom readers by using the discount code Chris10 at checkout from either of their two sites: or 

You will never know whether the air in your Pain Cave is doing you more harm than good unless you check.  There are ways to decrease the risk.  The first step is accepting that you have a problem. That was a tough one for me.  I’m glad I took it.

Do You Care?

Is the indoor air quality in your Pain Cave a concern to you? Would you instead not think about it? Does this information make you wonder? I wonder…Comment below!

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James Martin Sr
James Martin Sr
2 years ago

Thanks for the article Chris, I went and purchased a Air quality tester, I’ll shoot you my results once I get it in. Great Picture at the top!

Frank Kowalonek
Frank Kowalonek
2 years ago

Chris, You should take the same measurements outdoors to establish a baseline.

Lucia DeAngelo
Lucia DeAngelo
2 years ago

WOW amazing information, thank you for this in-depth research and share. With the rise of indoor training and riding on virtual platforms, this information is key!


[…] effects of chronic exposure to elevated CO2 and PM2.5 levels, as described in this previous post, Poor Indoor Air Quality – The Invisible Danger to the Virtual Cyclist, are a risk to anyone who exercises […]

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