8,153
edits
Changes
BSX
,no edit summary
=BSX Validity=
I have a number of concerns with the validity of the results of the BSX.
* '''No Limited independent validation'''. There is no independent validation a [http://link.springer.com/article/10.1007/s12283-016-0198-6 study by the University of Waikato] that found a good correlation between the BSX results and some measures of Lactate Threshold. I have a number of concerns with this study. It used the first generation of BSX, which doesn't mean that the device it doesn't workhas some rather obvious failings, but and it is does not compare the BSX against a significant concerngood reference standard for Lactate Threshold (MLSS). There are some independent reviews The study used three estimates of Lactate Threshold based on blood lactate testing; one is the common Onset of Blood Lactate Accumulation (see belowOBLA), but these are the other two were somewhat unusual. They found that the BSX was +/- 19 watts of OBLA, itself not really validationsa great measure of Lactate Threshold. So, the Gen 1 BSX showed a better correlation with a bad standard than research shows between those standards and the true Lactate Threshold (MLSS). The main conclusion I would draw from this study is that a crude estimate of LT from 10K pace is just as good as the crude estimates from an incremental stress test with blood lactate draws. <br/>[[File:BSX OBLA.jpg|none|thumb|150px|The Lactate Threshold estimates using OBLA and BSX, with the vertical ticks as 20w intervals. ]]
* '''Black Box'''. The BSX algorithm is proprietary and not clearly documented, which means it's hard to know if there is any scientific basis for their approach. BSX states that their algorithm is patented, but nowhere do they indicate what their patent number is. I believe it is patent US20130096403; see below for details.
* '''BSX Validation'''. BSX has performed their own validation but the results are not published. The reviews give some insight into the methodology that BSX uses, but the details are unclear. These reviews indicate that BSX did not use the gold standard of MLSS for [[Lactate Threshold]] in their validation. Instead they used an incremental treadmill test with lactate measurement from a blood draw, and relied on the rather poor Carmichael Training Systems determination of [[Lactate Threshold]]. I believe that this indicates that BSX has performed their internal validation against a seriously flawed baseline. (See [[Lactate Threshold]] for details.)
* '''Sensor Location'''. A minor concern is the location of the sensor on the calf, where it may be more affected by changes in biomechanics than using the quads.
=Testing BSX=
I performed a number of tests of the BSX. Other than a few tests when my hand I had an issue with excessive ambient light, the BSX always provided me with an estimate of my Lactate Threshold. The answer it gave depended directly on the input I gave the app about my 10K pace. As noted above, the estimate would vary wildly. Below is the data I captured from one of the tests. You can see the sudden rise in heart rate at the three minute mark that represents the end of the initial walk and the beginning of the running, and this is followed by a steady rise in heart rate. The red line represents the muscle oxygen saturation recorded by the BSX, and you can see that it detects the change from walking to running with a small drop, but thereafter remains relatively level. There is a slight drop from the first running section through to about the 15 minute mark, after which it levels off. You see a few small dropouts, but this might be an issue with the communications from the BSX to my watch. It's hard to see from this muscle oxygenation data that there is any indication of a change that would represent a lactate threshold. In fact it's hard to believe that the BSX is even really determining muscle oxygenation. (Note: the muscle oxygenation data is recorded as cadence data for compatibility.)
[[File:BSX LT Test.jpg|none|thumb|500px|Incremental Lactate Threshold test with the BSX.]]
I did all my tests with both the BSX and the [[Moxy]] for comparison. Unfortunately, I had a battery problem with my Moxy so I don't have as many samples to show. The image below shows the rising heart rate in blue, the BSX in red, and the Moxy in green. You can see that both the BSX and the Moxy drop as I transition from walking to running, but you'll notice that the Moxy continues to drop as the intensity increases. This is what I'd expect to see from a muscle oxygenation sensor. In my testing I've always seen the Moxy detect a drop in muscle oxygenation, and never seen one from any of my BSX sensors. I have no way of verifying whether the Moxy is accurate, but I can see that it is the least functioning.
Patent US20130096403 A1 (Apparatus and method for improving training threshold), which is a patent for determining the Lactate Threshold using an incremental stress test with an infrared sensor. I feel reasonably confident that this is the BSX patent, but I could not confirm this and BSX seem to carefully avoid any reference to the details of their patent. The patent describes an experiment using a 3 minute incremental treadmill run on 34 subjects, which looks like multiple aspects of muscle oxygenation (SmO2):
** '''SmO2'''. The basic measure of SmO2 showed a good correlation between SmO2 and Lactate, but only in 19 of 34 subjects (56%). The example correlation uses Lactate ranges 0.6 to 2.5, suggesting that the correlation might only exist at relatively low intensities.
** '''Rate of change of SmO2. '''This is the slope of the line drawn through the SmO SmO2 during a stage. Here the correlation existed only for 11 of the 34 subjects (32%). Here the chart shoes a Lactate range of 1.2 to 6.8, which is a much higher intensity and crosses what BSX consider to be the marker for Lactate Threshold (even though there is a fairly linear increase up to the 6.8 mark.)
** '''Magnitude of the reduction in SmO2. '''It looks like they do an exponential fit for the SmO2 and then find the rate of decay constant. This gives a correlation for 25 of the 34 subjects (73%). Here the charts are rather odd; the increment test chart shows Lactate in the range 0.6 to 2.0, but the regression chart only uses value of 0.6 to 1.3 (pretty much resting Lactate levels).
** '''Rate of decay of SmO2'''. Like the magnitude, this uses the rate of decay from the exponential fit, but this only gives a correlation for 9 of the 34 subjects (26%). The charts for this have a Lactate range of 0.8 to 4.0, a reasonable range for a Lactate Threshold test.
=Independent Reviews=
BSX pointed me to three individuals who have reviewed their device; Tony Vienneau (Slowtwitch.com), Matt Fisher (triathletesdiary.com), and Ray Maker (dcrainmaker.com).
* Tony's review on slowtwitch.com mentioned that he used the BSX to perform multiple tests (30-40). Tony noted that the muscle oxygenation value displayed on the BSX varied with fatigue, which was different to my results where the value seemed reasonably static regardless of activity level. Tony mentioned that he had a Blood Lactate test performed that corresponded with the BSX results, but gave no further details. Tony mentioned to me that he generally saw changes in displayed SmO2 that corresponded to intensity. He also found that he got an error if he ran at an easy pace with the BSX. Tony's review is available at [http://www.slowtwitch.com/Products/Electronics/BSX_Insight_5257.html http://www.slowtwitch.com/Products/Electronics/BSX_Insight_5257.html] and was published August 2015. * Matt completed a single test with the BSX at their facilities. Matt's review shows a plot from the BSX software that is not normally available to the end user, showing time against a relative concentration. This is intriguing, and I have similar plot from BSX for a couple of my tests. However, BSX wouldn't tell me what the substance was that they were plotting as "relative concentration". If you look at the chart on Matt's site, you'll see what is probably the raw data in red, showing a huge amount of noise, an orange line that appears to be a smoothed version, then a simple green line that is further smoothed. This is all very intriguing, but equally unclear. As an aside, Matt includes a blood lactate plot he had performed a few years back, which would not have a Lactate Threshold based on the criteria BSX uses (1+1 mmol/l rise). That's slightly ironic, but it highlights the problem with their blood testing methodology. You can read Matt's review at [http://triathletesdiary.com/blog-2/entry/general-blog-posts/playing-with-the-worlds-first-wearable-lactate-threshold-testing-device-from-bsx-athletics.html http://triathletesdiary.com/blog-2/entry/general-blog-posts/playing-with-the-worlds-first-wearable-lactate-threshold-testing-device-from-bsx-athletics.html] and was published August 2015. * Ray also completed a single test, and his write up includes the chart of blood lactate levels as well as some different charts from the BSX software. For the test Ray estimated his 10K pace as 6:05 min/mile pace, and the BSX indicated a Lactate Threshold pace of 6:03 min/mile, with the BSX blood test showing 5:42 min/mile. Ray's blog also includes a vaguely similar plot to the one Matt includes, showing noisy data in red. This chart is simply marked "estimated" on the Y axis and has a different scale with no units. This chart looks like a visual estimation of the breakpoint in the muscle oxygenation, something that other researchers have used. The review also includes some charts of probability, which is intriguing, but hard to interpret. You can read Ray's write up at [http://www.dcrainmaker.com/2014/09/bloodless-lactate-threshold.html http://www.dcrainmaker.com/2014/09/bloodless-lactate-threshold].html]* Another set of reviews that BSX did not mention were performed by Gabriel Hernando of zitasport.com. Gabriel has written five articles about his experiences with BSX, mostly covering the difficulty in getting it to work. Gabriel found that the BSX gave a Lactate Threshold that compared well with his Functional Power Test from cycling. You can read Gabriel reviews at [http://blog.zitasport.com/category/crowdfunding/bsx-insight/ http://blog.zitasport.com/category/crowdfunding/bsx-insight/] (this is in Spanish, but Google can translate it reasonably well.)
=BSX Gen 2 Changes=
The second generation of the BSX has the following changes: