Changes

* '''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. ]]

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.)

** '''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.)

* 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.)