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From Fellrnr.com, Running tips
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* '''Black Box'''. The BSX algorithm is proprietary and not clearly documented. This 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. Patent US20130096403 A1 (Apparatus and method for improving training threshold) looks like it could be for BSX, but I could not verify this.
* '''BSX Validation'''. BSX has performed their own validation but the results are not published. There are various blogs online that perhaps describe the validation that BSX performed, but the details are unclear. These blog entries 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.)
* '''3 minute stagesMinute Stages'''. The BSX protocol uses an incremental test with three minute stages, which does not appear to be a valid approach for measuring blood lactate directly. This is because blood lactate takes 20-30 minutes to stabilize for a given intensity. Of course, it is possible that muscle oxygenation would not be subject to this limitation as it is measuring a very different physiological parameter, but it is another concern.
* '''%O2 Display'''. In my testing, the BSX application showed a constant oxygen saturation level regardless of exercise intensity, typically 86 to 87%. This is in contrast to Moxy that showed a decline in oxygen saturation with increasing exercise intensity, roughly in line with the published literature. BSX has suggested that future versions of their software will present a more realistic estimate of oxygen saturation, and this problem should not indicate an issue with their validity. Personally, I find this a lack of even a relative change in oxygen saturation rather troubling.
* '''Invalid resultsResults'''. In my personal testing, the results of the BSX did not seem valid, but seemed to be based on what I told the application was my 10K pace, and the pace at which I terminated the test. The BSX indicated I had a [[Lactate Threshold]] pace of between 6:10 and 8:50 depending on what 10K pace I input and what pace I terminated the test. * '''Exercise ignoredIgnored'''. A bigger concern is I got the same indicated [[Lactate Threshold]] pace if I tell the BSX I'm performing a test, but don't actually do any exercise. Just sitting still and terminating at the same point gives pretty much the same result.
