VO₂ max is a measure of the maximum amount of oxygen the body can take in, transport, and utilize during intense exercise (AKA your aerobic capacity). It is one of the best indicators of your cardiorespiratory fitness. VO₂ max is typically expressed as milliliters of oxygen consumed per kilogram of body weight per minute (mL·kg⁻¹·min⁻¹). When interpreting a VO₂ max the term MET is often discussed, which is essentially another way of interpreting VO₂ max. A MET of 1 is oxygen consumption at rest. Higher VO₂ max values (or METs: 1 MET x 3.5 = VO₂ max) indicate a greater ability to sustain prolonged physical activity and perform demanding tasks that require endurance. In tactical populations such as firefighters, a higher VO₂ max can help support performance during activities such as stair climbing, hose advancement, victim rescue, and prolonged incident operations.
VO₂ Max & Heart Disease Risk
VO₂ max is not only a measure of fitness but also an important indicator of overall cardiovascular health. Research consistently shows that individuals with higher levels of cardiorespiratory fitness have a lower risk of cardiovascular disease, heart attack, stroke, and premature mortality. Conversely, low VO₂ max values are associated with an increased risk of cardiovascular events and all-cause mortality. Because cardiorespiratory fitness reflects the integrated function of the heart, lungs, blood vessels, and muscles, VO₂ max has been described as a powerful predictor of long-term health outcomes. Improvements in VO₂ max can contribute to reductions in heart disease risk factors, including hypertension, obesity, insulin resistance, and lipid profiles.
How Is VO₂ Max Calculated?
Several practical tests have been found comparable to laboratory tests for providing useful estimates of VO₂ max. For the purpose of this article, I will describe three different tests. It is important to note that all tests require both a warm-up and dynamic stretching prior to performance. Additionally, all tests require a heart rate monitor and timer. The VO₂ max value interpretation would be based on your age and gender.
Cooper Test
The Cooper test estimates VO₂ max based on the distance travelled during a maximal effort 12-minute run. Your VO₂ max is calculated using the following formula: VO₂ max = 35.97 x distance in miles − 11.29. For example, if 1.5 miles were completed the VO₂ max would be 42.7.
Bruce or Gerkin Protocol
The Bruce or Gerkin protocols estimate VO₂ max based on utilization of a graded treadmill test. In these tests, the treadmill is set at desired speeds (based on which test is performed) and the incline % advanced in timed increments. After the first 3 minutes of the tests the Gerkin advances every 1 minute whereas the Bruce protocol every 3 minutes. This test may, depending on fitness levels, require a treadmill that inclines up to 22%. One difference in the two protocols is the Bruce is a maximal effort test, whereas the Gerkin is stopped at 85% of heart rate max and considered a sub-maximal test. A trained professional should administer and score these tests.
Rockport 1-Mile Walk Test
For those individuals who cannot run as required for the Cooper test or safely perform a graded treadmill test, the Rockport 1-mile walk test² may be used. This test requires the firefighter to walk continuously as fast as able for 1 mile. The total time walked as well as the bodyweight, age, heart rate at conclusion of 1 mile, and gender is used to determine VO₂ max. The calculation is as follows (easier to use an online calculator): VO₂ max = 132.853 – (0.0769 x Weight lbs.) – (0.3877 x age in years) + (6.315 x Gender) – (3.2649 x time in minutes) – (0.1565 x heart rate immediately at conclusion).
So What Does My Score Mean?
The latest NSCA’s Essentials of Tactical Strength & Conditioning (2nd edition) recommends a minimum VO₂ max range of 39–45, or 12 METs, for structural fireground tasks.¹ While this is important, newer recommendations suggest age- and gender-based percentage interpretations. Additionally, evidence indicates that firefighters with a VO₂ max of less than 43 are 2.2 times more likely to be injured than those with a VO₂ max of greater than 48.³
Age-Based Averages for General Population
| 20–29 | 30–39 | 40–49 | 50–59 | 60+ | |
|---|---|---|---|---|---|
| Women | 31–38.9 | 28–36.9 | 25–34.9 | 22–33.9 | 21–32.9 |
| Men | 34–43.9 | 31–41.9 | 27–38.9 | 25–37.9 | 23–35.9 |
*Note: firefighter performance requirements exceed general population averages. If you have performed a VO₂ max test interpreted by a qualified professional and score below the functional range needed for fireground activities, your next step is to improve your cardiovascular conditioning. Keep in mind that the goal of improvement is not based on “performance” alone. Firefighters with improved aerobic capacity have a reduced risk of heart disease and are less likely to be injured on the job.
Improving VO₂ Max
Both high-intensity interval training (HIIT) and low-to-moderate intensity training improve VO₂ max via different physiological mechanisms. HIIT challenges the cardiovascular system by working near maximal effort, which increases the amount of blood pumped out with each heartbeat and the body’s ability to deliver oxygen to working muscles. Low-to-moderate intensity exercise performed over longer durations enhances heart efficiency by increasing capillary density and mitochondrial activity, as well as increasing the muscles’ ability to utilize oxygen. Together, these training approaches stimulate complementary adaptations that increase VO₂ max. For firefighters, you need the benefits of each training approach for your job.
To get started, please see the article “ TABATA STYLE TRAINING ” as well as other high-intensity interval training (HIIT) exercises in our video library. If HIIT is not feasible due to injuries or other issues, improvements in VO₂ max can still be achieved with consistent longer-duration low-to-moderate intensity exercises such as brisk incline walking, slower-paced stair training, cycling, or rowing.
References
- National Strength and Conditioning Association. NSCA’s Essentials of Tactical Strength and Conditioning. Edited by Brent A. Alvar, Katie Sell, and J. Jay Dawes, 2nd ed., Human Kinetics, 2027.
- Kline, G M et al. “Estimation of VO2max from a one-mile track walk, gender, age, and body weight.” Medicine and science in sports and exercise: 19. 1987, 253–9.
- Gerald S. Poplin, Denise J. Roe, Wayne Peate, Robin B. Harris, Jefferey L. Burgess. The Association of Aerobic Fitness With Injuries in the Fire Service. American Journal of Epidemiology: 179. 2014, 149–155.