Elite athletes have been measuring their VO2 max for over 50 years as a measure of overall aerobic fitness. VO2 max is defined as the maximum rate of oxygen consumption and is expressed in milliliters per minute per kilogram of body weight (ml/min/kg). Aerobic training improves VO2 max significantly. However, on its own is a poor predictor of athletic performance because it tells nothing about how efficiently the muscles are utilizing the available oxygen.
Lactate threshold has many definitions but is commonly known as the exercise intensity that an athlete can sustain for a specific period of time before their blood lactate concentration becomes too high. At a certain point lactate begins to accumulate faster than the muscles can remove it, and the intensity is no longer sustainable. A higher lactate threshold is a much better indicator of overall athletic performance compared to VO2 max because it provides insight on how the muscles are utilizing available oxygen.
Muscle oxygen saturation measures the balance between the supply and demand of oxygen to the muscles during exercise. Therefore, it is not only able to capture the supply of oxygen (VO2 max), but also how efficiently the muscles are utilizing it (lactate threshold). Measuring muscle oxygen provides the benefits of both VO2 max and lactate threshold testing.
With muscle oxygen, you can adjust training intensity, see how your muscles are recovering, and fatiguing during each workout. You can also complete lactate threshold tests without needing to pay for expensive lab tests.
VO2 max and lactate threshold tests are the most widely used indicators of performance for endurance athletes. Both provide valuable insights about an athletes overall fitness, but are also expensive, invasive, and need to be done regularly. Muscle oxygen saturation is a relatively new metric now being used to train daily because of the advent of wearables (and Humon). A muscle oxygen wearable is a great option for athletes looking to get the benefits of VO2 max and lactate threshold testing daily and outside of the lab.