VO2 max might be one of the most discussed—and arguably one of the least useful—metrics for endurance athletes. I’m not saying that your VO2 max isn’t meaningful or doesn’t correlate to your fitness level, just that there’s not a whole lot you can do with it beyond simply knowing what it is. But since triathletes (and endurance athletes in general) really do like to talk about their VO2 max, let’s dive into it. We’ll walk through what it is, why it matters (as well as why it doesn’t, and which metrics matter more), what physiological adaptations contribute to VO2 max improvement, and ultimately how to increase your VO2 max (alongside those other, more actionable metrics).
What is VO2 max?
VO2 max is short for “Volume of O2Maximum” where O2 stands for oxygen. Actually, it’s supposed to be written as “V̇O2 max” where the V̇ stands for “V̇olume per unit of time.” This quantifies the maximum amount of oxygen that your body can utilize during exercise, typically expressed as milliliters of oxygen per minute per kilogram of body weight.
That’s the proper, scientific definition of VO2 max, but that doesn’t really tell you what it is and why it’s considered to be an excellent indicator of fitness. To understand that, we need to discuss your aerobic and anaerobic energy systems, which combine to provide virtually all of the energy that fuels your muscles.
There are a few key differences between these two energy systems that are critical to this discussion: (1) Your aerobic energy system requires oxygen to convert muscle glycogen into fuel; your anaerobic system does not. (2) Your aerobic energy system can deliver fuel for hours and hours and hours; your anaerobic system can only deliver fuel for a short window of time (as in, minutes).
It’s also helpful to understand when and why your body uses one energy system versus the other. Given its greater staying power, your aerobic energy system is the first one your muscles turn to for fuel. As long as your cardiovascular system delivers enough oxygen to your muscles and your aerobic energy system can keep up with your muscles’ demand for fuel, your aerobic energy system continues to provide most of the fuel that your muscles need.
The aerobic energy system, though, is limited in the amount of fuel that it can provide by the amount of oxygen it receives from your cardiovascular system. When you’re working so hard that your muscles need more fuel than your aerobic energy system can produce, then your anaerobic energy system takes over and your ability to hold that effort level is limited to a relatively short duration.
So: your VO2 max is the oxygen limit that caps the fuel production capabilities of your aerobic energy system. And given that the aerobic energy system is the primary fuel source for all exercise that lasts more than a few minutes (as in, every triathlon and every triathlon training session), that seems like a pretty big deal.
Why does VO2 max matter in a triathlon context?
All of that brings us to why VO2 max matters for any endurance athlete: The higher your VO2 max, the more oxygen your cardiovascular system delivers to your muscles. The more oxygen available to your muscles, the more fuel your aerobic energy system can provide. The more fuel your muscles have, the harder they can work and the longer they can last, which sounds to me like the entire goal of endurance sports.
Why it doesn’t matter (on a practical level)
Outside of testing done at an exercise physiology or sports medicine lab, you can’t determine your VO2 max or measure your oxygen utilization while you’re exercising. If you can’t monitor your oxygen consumption relative to your VO2 max during exercise, you can’t prescribe training or develop race plans based on it. Have you ever seen a workout that said “go swim/bike/run at X% of your VO2 Max”? Nope, because there’s just no way to do that outside of a lab. Your VO2 Max is an interesting piece of data, but it’s not actionable data.
If it doesn’t matter on a practical level, what does?
Thankfully, it turns that your VO2 max in isn’t the only metric that represents your fitness. Professor of sports science Véronique Billat’s 1996 study established that your speed at VO2 max (vVO2max, or velocity at VO2 max) and the duration that you can hold that speed (tlimvVO2 max, or time limit at vVO2 max) provide as good as if not a better indication of your performance potential.
Professor Billat, along with many other exercise physiologists and researchers, also determined that an athlete’s pace/power at lactate threshold is an excellent proxy for their speed at VO2 max. And guess what? You can determine your lactate threshold heart rate and corresponding threshold pace/power fairly accurately using field tests (tests you do on your own, not in an exercise physiology or sports medicine lab). Beyond that, your heart rate and pace/power can be monitored during workouts using any multisport watch on the market, which means that you can prescribe training and develop race plans based on those metrics.
What happens when you improve VO2 max?
Going back to the scientific definition, VO2 max represents the maximum amount of oxygen that your body can utilize during exercise. Oxygen utilization is based on oxygen delivery to your muscles, which is the job of your cardiovascular system. And your heart is the primary driver of cardiovascular performance. Improving your VO2 max, therefore, happens when your heart muscle becomes stronger and is able to deliver larger amounts of oxygenated blood to your muscles with every heartbeat.
This also means that as this capacity increases, your heart doesn’t have to beat as frequently to deliver the oxygen required to fuel your muscles at a given effort level. Or, if you compare the same heart rate before and after your improvement efforts, your heart pumps a greater volume of oxygenated blood after the improvement—and therefore a greater maximum amount of oxygen per minute.
What is considered a “good” VO2 max?
An individual’s VO2 max is influenced by a range of factors including age, gender, altitude, and, of course, fitness. The average untrained man will have a VO2 Max around 35-40 mL/kg/min, and the average untrained woman will have a measurement of around 25-30 mL/kg/min. Well-trained endurance male and female athletes will often achieve values of 50-60 mL/kg/min and 40-50 mL/kg/min, respectively. (Drop these ranges by 5 for masters athletes.)
Strategies for improving your VO2 max
Before we get to the tactics for improvement, let’s set some expectations. First, studies such as this one by the NIH concluded that up to 50% of your ability to improve your VO2 max in response to training is influenced by genetics—meaning you can’t change that part with training. Also, the less fit you are, the easier it is to improve your VO2 max; if you’re already quite fit, you are potentially already near your physiologically-driven limit. Finally, no matter what you do, VO2 max will drop as you age, at the rate of about 2% per year.
For these reasons, it’s beneficial to focus on tactics that will both improve your VO2 max and also improve your pace/power at lactate threshold and your ability to hold that pace/power for longer durations. These more easily measured and monitored metrics are equally good representations of your fitness and have the potential to improve with training even after you have reached your greatest potential VO2 max.
So, with that backdrop, let’s talk about how to get faster, which is ultimately what all if this should be about.
One tactic for improving your VO2 max, your lactate threshold, its corresponding pace/power, and your overall aerobic fitness is to do—wait for it—a lot of work in your endurance (aerobic) training zone. No, it’s not terribly sexy or exciting, but there’s a reason why virtually all coaches describe endurance-effort workouts as the bread and butter of training. Training in your endurance zone, commonly referred to as Zone 2, is an excellent way to strengthen your heart muscle, improve VO2 max, and increase the staying power of your aerobic engine.
A second tactic for improving your VO2 max, your lactate threshold, its corresponding pace/power, and your ability to hold that pace/power for longer durations is to do (yes!) interval training. There are two distinct styles of interval workouts that promote all of these adaptations:
- Intervals that are 1-5 minutes in duration and at effort levels just above threshold effort (RPE 8 / 99-102% of LTHR / 105-120% of FTP).
- Intervals that are 5-20 minutes in duration and at effort levels at and just below threshold effort (RPE 6-7 / 93-99% of LTHR / 90-105% of FTP).
Before you put all your chips in the proverbial VO2 max basket, though, remember that your race-day performance is not solely based on metrics. Success in endurance sports is about going faster for longer, and yes, you can achieve that through improving your VO2 max and your speed and endurance at lactate threshold. But you can also achieve that by improving your movement economy, your fueling strategy, your pacing strategy and execution, and your mental skills. If it was only about the numbers, there’d be no reason to hold the race.