I came into the lab a skeptic, and walked out a very sweaty convert. You don’t need to be fast to benefit from this kind of testing. In fact, the slower or more unsure you feel, the more helpful it can be.
I’ll admit it: I walked into CTS’s lab feeling a little sheepish. I wasn’t sure if I really “deserved” to be there. VO₂max and threshold tests seemed like the kind of thing reserved for Olympians and Kilian Jornet.
But curiosity won out. I’m not one to turn down the opportunity to get more information about my body and training. I wanted to know: What could these tests actually tell me about how I run? Could data help me train smarter, race better, or just understand what’s going on in this weird, wonderful meat machine I live in?
I’m not extremely data-driven, but I do like to know if I’m training correctly and if my training is working. Doing a lactate threshold test and a VO₂max test was the perfect opportunity to check under the hood.
At CTS, I did two main tests: a lactate threshold test and a VO₂max test. Both are designed to gather data about how your body uses oxygen and produces energy under increasing intensity. Here’s the quick-and-dirty breakdown:
Both tests are commonly used to individualize training. Instead of relying solely on pace, heart rate, or effort (which are still useful), physiological data lets you and your coach tailor your work to your unique engine.
Threshold testing identifies the intensity at which your body switches from primarily aerobic metabolism to more anaerobic energy systems. If you think back to high school biology, “aerobic” means “with oxygen”, meaning your system has sufficient oxygen to meet energy demands primarily through fat and carbohydrate metabolism. Once you cross that threshold, oxygen delivery can’t keep up, and your body begins relying more on anaerobic pathways that produce energy quickly, but less efficiently, and that’s when you get fatigue-inducing byproducts like lactate.
Imagine your body as a hybrid car.
When you’re running at an easy pace, you’re cruising on the efficient electric motor, quiet, smooth, and built for long distances. This is your aerobic system, using oxygen to fuel your movement in a steady, sustainable way.
But as you speed up and hit a certain effort, your threshold, the car kicks over to the gas engine. It gives you a burst of power, but it burns fuel faster, creates more wear and tear, and can’t run like that forever. That’s your anaerobic system, which doesn’t rely on oxygen but builds up fatigue more quickly.
Threshold testing helps identify the exact pace or effort level where that shift happens, so you can train smarter, avoid burnout, and build both speed and endurance over time.
At CTS, this was measured through a graded treadmill protocol combined with blood lactate sampling, small blood draws taken at regular intervals to track how lactate accumulates in response to increasing effort. It’s a cornerstone for determining accurate training zones and avoiding the dreaded “gray zone” in endurance training.
VO₂max is your maximal oxygen uptake, the ceiling of your aerobic capacity. It’s a rough proxy for aerobic potential, but it’s just one piece of a much larger puzzle. In isolation, it’s not predictive of performance, but paired with threshold data, it tells you a lot about how efficiently you operate below your aerobic ceiling. These metrics help determine not only VO₂max, but also ventilatory thresholds, substrate utilization (carbs vs. fat), and overall aerobic efficiency. It’s one of the most comprehensive windows into how your body performs under stress.
I’ll admit that I was a little bit nervous. Running at max effort on a treadmill while breathing through a high-tech garden hose in front of a small audience is not exactly my idea of a good time. However, the test was actually significantly easier than I had built it out to be in my head, and my stress dreams about going viral for barfing into an oxygen mask were unmerited.
The team at the CTS lab, led by lab tech Renee Eastman and assisted by my coach, Cliff Pittman, helped me feel prepared and comfortable in the lab. First up was the threshold test: a progressive treadmill protocol where we increased speed incrementally. I wore a mask to capture gas exchange, and we took blood samples every few minutes to track lactate buildup. The length of the test varies for each participant, depending on your lactate threshold, but for me, this took about 40 minutes with a warm-up. Fascinatingly, my lactate levels started extremely high, as a result of pre-test nerves, but settled quickly. Anyone else anxious enough that it’s basically exercise? No? Just me?
After a short break and some much-needed hydration, we moved on to the VO₂max test. This is the one you might’ve seen on Instagram, athletes sprinting on treadmills with giant masks strapped to their faces, looking like Bane from The Dark Knight Rises. It’s over quickly, and the goal is to go until you just… can’t. Thankfully, my coach and Renee acted as spotters to make sure I didn’t go flying off the back of the treadmill. I was pretty nervous about this section, but actually really enjoyed the opportunity to go hard and get some really cool data.
When I stepped off the treadmill, lungs burning, I felt a little bit wrecked and completely curious. How did I do?
To my surprise, the data didn’t just confirm what I already suspected (my coach had actually pinpointed my threshold pace within one second of the test result, an incredible party trick)—it completely reframed how I think about my training.
My threshold pace landed exactly where I’d hoped, which is especially useful for an ultrarunner. My VO₂max came in a little lower than I’d like, but hey, who doesn’t love some room for improvement?
After the tests, Renee and Cliff walked me through a detailed debrief, helping translate the dense data into tangible training takeaways. With their help, I was able to dial in my training zones with more precision. The default heart rate zones on apps like Strava and TrainingPeaks can be surprisingly inaccurate; mine were all off by margins significant enough to be unusable. I was also able to identify VO₂max as an area of potential growth, and confirm that I’m very metabolically efficient at slower speeds, the ultimate ultra flex. We also saw that I’m pretty good at clearing lactate, another key indicator of aerobic fitness.
Altogether, the results painted a textbook picture of an ultrarunner’s physiology, one that validated the work I’d been doing, highlighted my biggest opportunities for growth, and gave me and my coach the tools to fine-tune my training even further. I walked away not just with some fancy charts, but a real understanding of how that translates to practice. I needed to run my workouts harder, keep developing top-end speed out of competition season, and my metabolic data suggested I could dabble in higher-carb fueling if I was so inclined.
I came into the lab a skeptic, and walked out a very sweaty convert. You don’t need to be fast to benefit from this kind of testing. In fact, the slower or more unsure you feel, the more helpful it can be.
These tests are incredibly helpful for anyone looking to improve, whether you’re training for your first ultra or chasing a PR at your tenth 100-miler. If you’re training with consistency and purpose, adding this layer of physiological specificity can sharpen your strategy and help you train smarter. Even though the oxygen masks, finger pricks, and generally being a sweaty guinea pig may seem intimidating, it was way more approachable than I initially thought.
You learn where your actual training zones are. I’ve worked with my coach on better calibrating my RPE, but environmental factors and fatigue can skew perception. Threshold testing helps calibrate your workouts with precision and takes some of the guesswork out of establishing your training intensities.
Using the metabolic data, I’m going to make some adjustments to my fueling plan. Seeing the exact breakdown of how my body burned fat at lower intensities and carbs at higher intensities gave me the confidence to increase my carb intake.
You can train smarter, not just harder. Understanding your physiological profile helps you get the most bang for your buck, especially if you’re juggling training with work, family, and life. I’ve been training consistently for about eight years, but I’ll be honest – I’ve occasionally had a nagging voice in the back of my head kick in during workouts and easy runs, asking Have you actually gotten better? Are you running too hard? Are you running too slow? Are you actually doing any of this right?
Throughout the test, Coach Cliff held up a clipboard with an RPE (Rate of Perceived Exertion), a subjective measurement of the effort, to record alongside my test. This was a nice gut-check on how I’ve been calibrating things and helped me further dial in RPE for workouts down the road.
Now, I have data to back up everything I’m doing, and honestly, my only regret is not doing this sooner. I’ve always been skeptical of data overload, or not knowing exactly what to do with the information once I get it.
Let’s clear up a few common misconceptions. First, the idea that “only elites need this” couldn’t be further from the truth; if anything, recreational athletes often stand to gain the most from targeted testing, since they typically have less experience calibrating their efforts. Goodness knows I could have skipped years of inefficient grey-zone running with this information. Second, while testing can seem expensive (for CTS athletes, lab testing is $250, and $300 for non-CTS athletes), it’s better viewed as an investment, one that can save you months (or even years) of trial-and-error training. Plus, it costs about the same as an entry-level GPS watch.
The CTS lab is located in Colorado Springs, but talk to your coach about options that might be available closer to you. Many university exercise physiology departments offer VO₂ max and lactate threshold testing to the public, and they often have high-quality equipment and trained staff. You can also search your area for Sports Performance Centers or Human Performance Labs. Just be sure to loop your coach in first; not every lab uses the most accurate protocols or up-to-date equipment, and your coach can help you find a facility that will give you reliable, actionable data.
And finally, no, your watch doesn’t give you the same data. Wrist-based VO₂max estimates are just that, estimates, based on pace and heart rate, and they can be wildly inaccurate, especially in variable terrain like trails and mountains. The heart rate
The value of testing isn’t just in the numbers; it’s in the interpretation. After the test, the lab tech, Renee, provided a detailed breakdown of my results with my coach, along with practical takeaways for training. If you’re going to do this, make sure you have someone (ideally a coach) to help translate the data into action. I’m already implementing takeaways, like correctly pacing threshold workouts, into my training.
If you’re self-coached, even just learning where your aerobic and anaerobic thresholds lie can reshape how you build long runs, workouts, and recovery.
Doing these tests didn’t turn me into a different runner overnight. But it gave me a new language to understand how I train and what I’m asking of my body.
I used to think testing was for pros or people chasing podiums. Now I know it’s for anyone who cares deeply about their running and wants to treat themselves like someone worth investing in. Testing helped me tap into a new level of body awareness and better own my journey as an athlete.
One of the biggest takeaways for me was how fun it was to spend a day geeking out about running and science with other adults who get genuinely excited by terms like ventilatory threshold, especially science that helps me understand myself and my training on a deeper level.
Beyond the charts and data, the experience itself unlocked a new level of excitement around my training. It felt like a way of saying out loud, “This matters to me. I care about this.” And sharing that moment with a team of people who were just as stoked, if not more, about a random lady’s metabolism? That was pretty cool.
Whether you’re chasing a PR, tackling your first 100-miler, or just want to train smarter, physiological testing might be the key to unlocking your next chapter.