Measuring Fitness: VO2 and Other Indicators Explained

By Dr. Sasha Stolz

measuring fitnessMeasuring fitness levels is an integral part of today’s science driven coaching.  You have probably heard the terms VO2 max (maximum volume of oxygen) , LT (lactate threshold), and maybe even Aerobic Threshold. If you own a fancy GPS watch, like the Garmin, you may have even seen predicted values for your VO2 max and max heart rate. In this article we will define VO2 max, LT, Aerobic Threshold and discuss the usefulness of laboratory testing versus predicted values. In part two, we will discuss how to implement your results along with max heart rate into your training plan.Let’s start with VO2 max. In simplest terms, it is the Volume of Oxygen the body consumes, or rather uses in one minute of maximal exercise. VO2 max testing, when done in a clinical or laboratory setting gives you a value that is predictive of your fitness level and endurance ability. This number is typically between 30-60 ml/min/kg in most people but can be higher or lower depending on fitness levels.

EKGTheoretically, the more oxygen a person can use during high level exercise, the more energy (ATP) a person can produce. VO2 max testing is the gold standard to cardiorespiratory fitness because the muscles need oxygen for prolonged (aerobic) exercise, the blood carries oxygen to the muscles and the heart must pump adequate amounts of blood to meet the demands of aerobic exercise.

All things being equal, a higher VO2 max number is desirable but it doesn’t always mean someone with a higher VO2 max will be faster than someone with a lower VO2 max value. There is a subsequent value that, when combined with the overall VO2 number gives one a better predictor of efficiency. This metric is vVO2 or Velocity at VO2 max. This measurement is how fast you were running or cycling when you reached your VO2 max. This number is a valuable metric to base you speed workouts on which in turn improves your overall VO2 max.

lactate threshold for measuring fitnessMoving on to LT or Lactate Threshold. Lactic acid is a byproduct of exercise which makes the muscles burn and may contribute to fatigue.  Athletes are always producing lactic acid during exercise, even at low intensities. Muscles are constantly burning lactic acid and using it as a fuel.  At low intensity the muscles easily recycle as much acid as is produced.  The higher the intensity is, the more acid is produced by the muscles.  When the body can no longer remove the lactic acid faster than it’s produced, this tipping point is called Lactate Threshold.

Just below LT, an athlete is working hard and acid levels are moderately high, but it does not accumulate.  Speeding up just a little will cause lactic acid accumulation, which leads to muscle fatigue and damages the muscles. In conjunction with the other values we are discussing today, knowing your LT will enable you to work out most efficiently.

heart diagramAerobic threshold (AeT) is the optimal intensity (wattage, running speed and/or heart-rate) for developing endurance.  At aerobic threshold intensity, the body is recruiting almost all of the slow-twitch muscle fibers, but not yet recruiting any of fast twitch fibers.  In short, slow-twitch muscle fibers are the endurance fibers that burn fat and some carbohydrates for fuel while fast twitch fibers are our sprint fibers that burn carbohydrates for fuel.

Most athletes, without the benefit of physiological testing, overestimate the intensity required to exercise at AeT.  Using optimal intensity for basic endurance training maximizes fat burning and minimizes recovery time and injury risk.  Most athletes perform basic endurance workouts at an intensity that is way too high.   Conducting basic endurance workouts at optimal intensity is much more efficient, enabling increased training volume as well as greater frequency and better quality speed workouts. If you find you are chronically injured, plateaued in your training and your last PR was longer than you can remember, as a coach and a doctor, this would be the first metric I’d look at. Are you actually training to hard?

So where does this leave us when it comes to clinical testing versus using predicated values? Clinical testing requires the athlete to be hooked to a breathing mask with a hose connecting to a computer. The athlete then exercises on a treadmill or bike for 6-24 minutes with intensity gradually increasing over time until the athlete achieves their threshold for exercise. Because VO2 max is a measurement of oxygen consumed during exercise, to get the most accurate measure then it makes sense to test in a clinical setting where the concentration of oxygen inhaled and carbon dioxide exhaled can be measured through a ventilation mask. Therefore, it follows that a predicted value that a device provides without measuring ventilation would not be as accurate as clinical setting.

By accurately measuring fitness, all of these metrics, combined with knowing your maximum Heart Rate, can help you and your coach put together a training program that increases your endurance and speed while decreasing your recovery time and injury risk.

In the next segment, we will discuss how to incorporate these values into your training plan.