Testing protocols and the BSX insight

At Source Endurance we know that being on the cutting edge of research and technology makes us some of the best at what we do. Having attended the BSX insight launch in Boulder, Colorado this past year, we came away with valuable insight into the future of performance testing. Wanting to learn more about the BSX unit, we decided to run our tests, share with our readers the results and discuss some of the potential advantages as well as limiting factors of the BSX product. Additionally, we wanted to convey the importance of the testing that we do and how it benefits our athletes.
The BSX Insight is a device that uses LED lights to look into your blood and report the rate of deoxygenation. The LED lights refract off of your hemoglobin and report the level of deoxygenation that is occurring back to an app on your phone which is connected to your HR monitor or Power meter. The goal of the BSX Insight is to “find your Lactate Threshold” by design its true function is to measure rate of deoxygenation and combine that data with the watts recorded during the test from your power meter thereby calculating your Lactate Threshold power. BSX has deemed a certain amount of deoxygenation your Lactate Threshold. Below is a graph representing the results of BSX “Lactate Test” protocol. Below is a picture representing deoxygenation over time during a test and as long as the graph is consistent between all athletes, BSX believes they can measure LT by tracking deoxygenation. The red line is the Oxygen concentration in your blood and how it changes as you increase your effort in a step test. At a certain point on this deoxygenation graph you have reached your lactate threshold.
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Another testing protocol that has success for athletes is a field test. This is a vastly simpler test. A field test is not only free but done correctly can yield a result within 5% of  lab test results and is repeatable. To correctly apply field testing you first have to find a stretch of road where you can ride a time trial without interruption and can apply certain principles and control certain factors. Some Training Peaks articles call for 20 minute field tests. Based on hundreds of Lactate tests and application of studies into field testing and current data from Source Endurance Athletes 20 minutes seems a bit too short. According to this study specifically “Peak Power Output, the Lactate Threshold, and Time Trial Performance in Cyclists” between a 20 minute time trial and a 90 minute time trial, a 90 minute Time Trial in Cyclists correlates closer to a lab style Lactate Threshold test than a 20 minute Time Trial. At Source Endurance, if we have an athlete that can’t get into one of our testing labs then we will design the best field test possible. That process is described more later.
Lactate testing is a closer comparison to a 60 minute effort under “ideal conditions.” Ideal Conditions being below altitude, well fueled, rested, low fatigue. Many of these factors are impossible to come by, making field testing a hard thing to master and hard for a coach to apply. It takes time and many athletes data to find a field test scenario that measures closely to an athlete’s lab test but once you have a few data points on a stretch of road and a length of time then you have a free, repeatable system of testing and getting relatively close to a riders Lactate threshold without a lab setting but this is not an ideal measure of Lactate Threshold.
Last year Source Endurance opened a Training Center in Fort Collins, Colorado. Inside the Source Endurance Training Center of the Rockies is a modest Lactate Testing facility. Using a “Nova Biomedical, Lactate Plus, Blood Lactate Meter,” a computrainer, and a proven testing protocol we test athlete’s blood lactate with a step test to find their power and heart rate at Lactate Threshold.  For the purpose of this article we will define Lactate Threshold, LT, and FTP as the point at which your body can no longer buffer acidity in your muscle, that acidity leaving the muscle with a molecule of Lactate, we measure the Blood Lactate concentration, bLc, finding Lactate Threshold at the point of exponential increase in blood lactate concentration.
Blood Lactate Curve BSX article
Above represents a blood Lactate Curve for a step test that was done in the training center in concurrence with a BSX step test using the BSX Protocol. It is important to note that the BSX Insight’s testing protocol is not the same as most Lactate Threshold lab testing protocols. This makes sense considering they are measuring different things, blood lactate concentration vs. blood deoxygenation.
The BSX Insight is a small device that fits into a sleeve held closely to an athlete’s calf muscle
Picture Courtesy of BSX website.
The BSX flashes LED lights into a rider’s calf muscle and the LED lights refract at different rates off of the hemoglobin. The rate of refraction is changed by how oxygenated the hemoglobin is. By measuring the change in deoxygenated hemoglobin across a step test BSX insight claims that it can measure Lactate Threshold. Below is another graph from the BSX website describing a bit of how they determine Lactate threshold indirectly by measuring deoxygenation.
Although this is a very innovative new device it has some issues. After a few tests on one of our athletes in one week, the BSX had hugely variable results from the next day and next week’s tests. Where a blood lactate lab test a few days a week are all very close, within 3% of each other wattages, which to note is also the variability of power meters. The BSX results would yield results for the step test up to 50% difference in wattages.
Most of this variability likely came from the nature of the testing. During the Blood Lactate lab test in parallel with the BSX test on the computrainer the results of the Dmax blood lactate test were 270 watts at lactate threshold where the BSX gave a threshold result of 275 watts
The BSX automatically creates your testing stages by 20 watt intervals based on two numbers, what wattage you can ride at “a talking pace” and your best 40k power. The 40k power input is really what creates your stages, remember a 40k depending on your fitness level is pretty close to a 60 minute effort depending on the terrain, this is a Lactate Threshold effort similar to a field test. The talking pace metric changes the stages less. In some ways we wish that this was a bit more objective. Ask for a best 3-4 hour power instead of “a talking pace” which is hard to interpret. When putting in a talking pace metric for the athletes that tested in the lab we put in the bottom of his aerobic zone which led the BSX to create a step test with 400 watts as “estimated threshold” knowing this athletes previous tests that wattage for LT was not possible so we had to manipulate the BSX to figure out what number it wanted as a “talking pace” and 40k power to make the step test reasonable. These inputted metrics will drastically change the results of your BSX step test if inputted incorrectly.
According to BSX no device is perfect and it helps to be on a trainer when performing LT tests with the BSX and taking out as many variables as possible with power meter calibration and outside variables. The biggest issue we have with the BSX at Source Endurance is the jump between physically measuring blood lactate to find Lactate Threshold vs. measuring deoxygenation and using to reach a power at Lactate Threshold. Similar to the field test discussion controlling as much as possible, you can get close but to say the BSX delivers real time Lactate Threshold measurements is just not true.
According to this study “Reproducibility of Measurement of Muscle Deoxygenation in Children During Exercise” Measuring muscle deoxygenation can be done very consistently. Deoxygenation is a measure of effort but nothing will be as accurate as a blood lactate threshold test measuring blood lactate concentrations.
Since outside is free, so are field tests. This seems like a large portion of the article for what should be the most simple of tests. A field test is very complex to get right consistently if your goal is to be as close to a lab test as possible and repeatable. Finding a repeatable field test is easy but making a field test within a certain percentage of a lab test and repeatable you have to take into account many variables. Field testing almost doesn’t fit in this article but it is a huge tool and is what BSX hopes to make more accurate and measure “on the fly.”
To perform a proper field test you have to first test the field test. If you go out and ride 60 minutes all out on a rolling road, you will likely fatigue very quickly and will show a pretty low wattage for the 60 minute average. Since likely you are not riding the 60 minutes under ideal conditions, you have to shorten the field test. According to this study “DEFINING THE DOSE OF ALTITUDE TRAINING” 5500 feet, the altitude of Boulder, most of Fort Collins and Denver accounts for a decrease in performance by 6-12% for aerobic intervals. If you go further up in your field test to 9000 feet then there is an even greater loss. That’s already chopping off about 10 minutes from the 60 minutes that Lactate Threshold power corresponds too under ideal conditions. If you are doing this on a climb for 50 minutes you will likely be way higher than the 5000 ft start of the climb. If you are not at altitude like most athletes you will likely have to find a rolling road. With changing inertial loads is hard to keep a consistent power, downhill vs uphill, taking away from another ideal condition.
Another huge factor is the mental factor of completing a long effort for a field test. You will fatigue the mind before you will fatigue the legs. There is not specific study to quote here but from experience we know that some days completing some 5 minute threshold intervals can be draining, so the mental suck from a 50 minute effort needs to be taken into account to get as lab data as possible.
One of the best example is in Fort Collins Colorado. We have a specific field test protocol and is based on over 40 athletes and their data for over 50 field tests on a certain stretch of road. Rist Canyon is a 9 mile climb, close to town with the ability for an ideal and controlled warm up the fastest rider complete the climb in about 40 minutes but most athletes would take 48-55 minutes to complete the climb. Taking Lab data for all these athletes and applying it to the time trials up Rist Canyon we have come to an ideal field test of 40 minutes up Rist Canyon is within 5% of Lab tests making it a very good tool for re testing and tracking Lactate Threshold without time in a lab setting. No Field test is perfect if you have a coach that can apply Lactate Threshold power numbers, confidently interpret the power or heart rate data, and terrain then this is a viable tool. You also don’t have to have a field test this specific, if you are just looking to see if your training is “working” you can do a 20 minute test but do not be misled this will not represent your Lactate Threshold. Here is an example of a field test TT for 40 minutes that corresponded to within 5% of the riders LT Lab test. This may seem self-confirming, a rider pacing a LT field test off of his current LT power or HR numbers in this case the rider had only HR visible to pace the TT by but the goal of the test is the best power possible so we try not to let the power numbers we already have pace your TT. As a coach we also look at the file very closely. If the 5 minutes of the field test was 150% of LT then the athlete likely paced the test off of a lower LT number or rode too conservatively and we can take that into account when applying this to changing Lactate Threshold number and zones.
Here is an example of a good power test performed on the described course.
Rist Test
As you can see the athlete above for the near 45 minutes rode at an intensity factor of 1.02 meaning 2% higher than their current Lactate Threshold outlined in their training peaks. While 2% seems like a small margin, when tracking field tests every few months you can only hope for consist 2% growth every month in longer aerobic intervals like this.
Lab testing. This is the gold standard for finding Lactate Threshold, the end game being creating training zones, retesting repeatability, and increasing your Lactate Threshold to increasing the efficiency of your training. Assuming that your Lab tester is experienced and the power meter is accurate, this test will tell you your Lactate Threshold wattage and Heart Rate the inaccuracy only being the +/- 1.5 percent wattage if you are on a computrainer. Like the BSX Insight, Blood testing uses a step test on a trainer. Usually 4 minutes stages your coach will measure your blood lactate after each stage. As the power stages increase your blood lactate will stay relatively the same until you start to accumulate anaerobic by products, acidity, measured in the form of Lactate in the blood. At lactate threshold your blood lactate is increasing exponentially.
Blood Lactate Curve BSX article
Comparing the power data to HR and utilizing HR zones is always helpful in confirming results and tracking fatigue.
Heart Rate Curve tst
At the Source Endurance Training Center we also take into account your power meter readings during warm up. If you power meter is 5% higher than the warmed up, recalibrated computrainer, we recommend looking at better power meters, but also we will give you two numbers for lactate threshold wattage, your lactate threshold wattage based on your power meter as that is what you train by and the lactate threshold wattage from the computrainer which will be the most accurate.
In Conclusion, the BSX insight is an innovative step to skipping the fees of Lab testing but the measurement of deoxygenation will not cut it in comparison to the accuracy of measuring blood lactate in a step test. Field tests can be utilized to confirm Lab tests and better track threshold over time without huge amounts of money and time in the lab but this takes time, interpretation, and a good coach to be best incorporated into your training.  Pick your method based on what you need for accuracy and what you have the time and money to complete.


  1. Ross on July 30, 2015 at 4:06 pm

    Can explain more about the variation of your test results you saw with the BSX.

    • Zack Allison on August 11, 2015 at 9:16 am

      Hey Ross, sorry for the late reply. I think the variations between BSX tests from test to test come mostly from the variability of the athlete performing their own test. Logan, the testing athlete did a first couple tests outside, that didnt work at all, although you are supposed to be able to do the BSX test protocol anywhere, the problem was in keeping the power consistent to match the test protocol. The other control issue is with the BSX that I think can change results drastically is just how the BSX “measures” Lactate, they dont, they measure deoxygenation so if you are not performing the test under every control possible, like on a computrainer under the same conditions for rest, hydration etc, as the last test then you will get skewed results. You can get varying results taking blood on a computrainer in a blood lactate test but its a different scenario and more stable than the BSX using LED lights to read deoxygneation and make assumptions on Blood Lactate. Hope that helps.

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