In early 2024, we began a concerted effort to improve our physical fitness, partly with a goal of maintaining our active lifestyle as we aged. We wanted to keep participating in recreations such as hiking and scuba diving well into the next decade or two. This would require reasonable levels of strength, balance, and cardiovascular fitness, attributes that would naturally decline as we aged if we didn’t consciously maintain them. In fact, the first thing we discovered on starting to exercise is how much decline had already taken place. And we’d also need to avoid a chronic illness or accidental injury, as either would accelerate the decline or put us out of action altogether.

Scuba diving in the Maldives, left, and, hiking in North Cascades National Park.

A key measure of cardiorespiratory fitness is VO2 max, the maximum rate at which a person can process oxygen during physical exertion. In Outlive, author Peter Attia expounded the importance of this metric: people with high VO2 max scores relative to their age-group peers live much longer and healthier lives. Attia also discusses VO2 max in detail in the podcast episode Exercise for aging people.

VO2 max essentially measures what we are capable of physically—the lower it is, the less you can do—and it naturally falls over time. Studies indicate VO2 max declines about 10% a decade until age 50, and then it can drop up to by 15% a decade after that. Attia shows a table with VO2 max score ranges by performance groups, shown below, and age and sex. Women have a lower VO2 max than their age-equivalent male peers, and the range for each performance group falls with each decade. For example, an elite score for a woman in her 20s is 53, but elite for a female in their 60s is only 40.

Attia encourages his patients to be in the elite top 2% of their age and sex performance group. If they achieve that, then he tasks them to aim for elite, but for two decades younger. The rationale is to get a high VO2 max now to counteract the inevitable decline. He gives an example of hiking in the mountains, an activity that requires a VO2 max of about 30, roughly the 50^th percentile for a 50-year-old woman. If a woman that age wants to continue hiking into her nineties, she needs to have a VO2 max now of 45 to 49 so that she will decline to around 30 as a nonagenarian. Unfortunately, we gave up a bunch by starting so old, but better late than never.

With this in mind, one of our fitness goals was to improve our VO2 max scores. Fitness watches and VO2 max calculators can produce an estimate, but the gold standard is an exercise stress test in a lab measuring ventilation and the concentration of oxygen and carbon dioxide in the inhaled and exhaled air. VO2 max is reached when the oxygen consumption stabilizes despite an increase in workload.

In researching options in our home of Seattle, the national chain DexaFit had a good reputation and offered both VO2 max testing plus another health metric we were interested in (DEXA body composition scan). We had our first appointment in May of 2024 to obtain a baseline. The VO2 max test takes about 10-15 minutes and typically is done on a treadmill or exercise bike. We went with the treadmill because that is how we were planning to train.

VO2 max test at DexaFit Seattle

Over the following year, we trained to improve our VO2 max once a week using Attia’s recommended 4×4 protocol. This consists of four minutes of steady state exercise at maximum exertion, followed by 4 minutes of passive recovery to bring our heart rate back down to 100, repeated six times. We initially used a treadmill, and later switched to an elliptical machine and occasionally use an exercise bike.

We returned to DexaFit every three months to gauge our progress. In this period, James’ score increased steadily, with an overall gain of 25%, a nice improvement. But Jennifer’s decreased with each test, dropping 14% overall. She fell from ‘high’ relative to her age-equivalent peers, to ‘above average’.

We initially assumed she must not be training hard enough. But her heart rate was reaching into the 170s. And near the end of a 4-minute set she was feeling the burning sensation that can occur during intense exercise, indicating she was working near her anaerobic threshold. Also, she wears a CGM (continuous glucose monitor), and her blood sugar often was spiking as the readily available glucose was depleted and her body released more, another indicator that the intensity was fairly high.

Training VO2 max on an elliptical machine.

Given that VO2 max is only expected to decline 15% in a decade without any training, that much of a drop in one year indicated a possible cardiovascular health issue. We researched online for an explanation, but couldn’t find anything beyond cardiovascular problems. And we raised this concern with DexaFit, who didn’t see a problem with the dropping score and had no credible theories to explain it.

To determine if we were dealing with a health or a test issue, we scheduled a cardiopulmonary stress test at the University of Washington (UW) Lung Function Testing Clinic, the absolute gold standard in VO2 max testing in our area. As expected from a medical facility, the test gathered much more data than those at DexaFit. After spirometry tests to measure lung function and other respiratory tests, Jennifer was hooked up to a breathing hose, similar to DexaFit, but also to a blood pressure cuff and multiple body probes to gather EKG (electrocardiogram) data.

Cardiopulmonary stress test at UW.

The medical test protocol was quite different from DexaFit’s, where the treadmill was immediately ramped to 5 mph after the warmup, and Jennifer ran the entire time. The UW test protocol began at 1.7 mph with a maximum speed of 4.2 mph, and she walked for all but the final 3 minutes.

Since the exertion wasn’t as difficult, Jennifer wasn’t very hopeful that the VO2 max score would be any different that DexaFit’s. But the maximum recorded score was 50.5, putting her at elite for her age group 2 decades younger. This result was fundamentally different from the DexaFit score of 32, or above average for her age group. And, most importantly, it meant she didn’t have a cardiovascular health issue.

Since the DexaFit numbers were off by such a large margin, the next problem was finding a lab where we could get an accurate test. The UW test was only available with a doctor’s referral, so not really an option. The other choices in the Seattle area were surprisingly limited, but we did find a new lab just opening up in Bellevue, Belmar. Their goal was to bring true medical-grade testing to the general public, beyond the available consumer tests. We got an appointment a couple of weeks after Jennifer’s UW test, allowing us to make a good comparison between the two.

We were impressed with the Belmar testing—the equipment and testing seemed identical to that of UW, including detailed spirometry and other airway tests. They also have a cardiopulmonary medical doctor on staff to really dig into the details when interpreting the results, something we really appreciate. And they understand their equipment and the test protocols well, and carefully calibrate the equipment before each test.

Spirometry and cardiovascular stress testing at Belmar

But the most important factor was the test results. And they were identical to UW, giving Jennifer a score of 50.6. We’d found a lab whose results we could trust.

We’re not really sure why Jennifer’s DexaFit VO2 max scores were so low. But that matters not. What is important is that we both have good scores and a reliable test source to ensure we are maintaining our fitness levels so we can hopefully stay active for many years to come.