Lactate Threshold Testing

To follow up on the last article on fuel efficiency testing, I decided to undergo a Lactate Threshold test to further define my zones in training (and to test out another gadget!). This was done using the BSX system, which measures muscle oxygen during exercise and estimates your threshold from this value. Admittedly, this test wasn't as pleasant as the fuel efficiency test, as it took me to failure after around 40 minutes on the treadmill. However it did confirm a few things and I found it very useful.

What is involved?
The BSX insight lactate threshold testing unit is a non invasive test which is different from the typical lactate testing involving taking small repeat samples of blood. I really like the reviews from DC Rainmaker so I will link his review here rather than rewrite something that has been done before. In summary however, it is a device that is relatively easy to use and repeatable. It is a shame that the device has been discontinued but I am still interested in utilising it and then testing it against the more traditional blood test version.

The basics involve measuring the oxygen level in the muscle of your calf while exercising. Based on the principle that the muscles utilise oxygen during exercising in order to produce energy, the BSX Insight measures this oxygen content and displays a percentage of oxygenation in that muscle (Sm02). As you exercise at higher intensities, there is a build up of lactate concentration from this process and also a corresponding decrease in the content of oxygen in the muscle. Typically, what happens in a progressive run test, is that Sm02 goes down steadily as intensity increases but then suddenly it drops exponentially, which is the sudden gradient change that you see in typical lactate threshold tests. The device will report the level that it predicts your threshold is, based on this sudden change. The corresponding heart rate (or intensity) is the threshold that you can sustain, otherwise know as the lactate threshold.

Why is it important?
Lactate threshold has traditionally been a metric that athletes have used to determine the maximum level of intensity they can sustain for long periods without "blowing up" or fatiguing rapidly i.e.. If you can sustain this maximum, you will perform better. Knowing this number is important in training and races so you can keep to your zones. Typically athletes can go above this threshold for a certain period of time before rapidly fatiguing. This time that athletes can sustain above threshold is a different metric that is sometimes referred to as functional reserve capacity (FRC) but I will not go into that today.

Lactate threshold is different between individuals and is also different between the same individual at different levels in fitness. An "untrained" individual may have a lower threshold than that same individual after some months of training. Most formulas to work out threshold are based on age, max heart rate and resting heart rate, and do not take this change of fitness into account. Hence they are often advocated as a "ballpark" figure or estimate.

What about my FTP?
Functional Threshold Power is another way to get similar results if you use a power meter on the bike. I personally find it much more useful than my lactate threshold heart rate or speed, particularly when running, as there are many other factors that influence heart rate and speed, namely simple things such as length of training, heat, ingestion of caffeine and gradient of the run, ride. In saying this however, I do like having another metric to use as a guide. Knowing that you can hold a certain speed at a certain heart rate or matching power and heart rate, helps determine if there are is any disparity and can warn you that something isn't right. Further, threshold ability can change based on factors such as muscle fatigue as well. You may be feeling fine with respects to heart rate on a run, but the legs just cannot go any faster despite your efforts. This is typically seen at the end of a long session such as a run or in the late stages of a race. Threshold heart rate alone will not help guide your efforts here.

Take home message
Although there are some limitations, in my opinion, the use of the lactate threshold test is a useful metric to obtain in order to "dial in" your efforts. When complemented with your FTP and knowing your maximal aerobic function (MAF), you can better tailor you efforts or zones to get the most from training, or more commonly to just slow down.
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