I've been working with the Moxy Muscle Oxygen Saturation Monitor for some while now and I'm still trying to properly understand the information that it is producing.

I think my biggest problem is that the data seems to be extremely inconsistent and there does not seem to be any sort of concrete explanation for this, not unlike Heart Rate Variability data.

About a week or so I did a little session which involved riding at around 65% of my Functional Threshold Power (FTP) for about 45 minutes, I then rode for a couple of minutes at 100% of my FTP. Following this segment I performed 10 thirty second efforts at 128% of my FTP.

My observations on this session are that unsurprisingly for the initial period SmO2 and tHb remained fairly stable and the initial 100% effort caused depression of both tHb and SmO2. Once I started the 30 second efforts at 128% of my FTP the SmO2 readings dropped off quickly and in the short pauses recovered quickly but incompletely. This pattern was repeated with a steadily decreasing SmO2 level which ended up at around the 50-60% level. This was pretty much what I would have expected, the data is shown below.

Today I repeated this session, I used an almost identical trainer control file so the timings and wattages were identical other than my adding a 10 minute isopower effort after the thirty second interval segment and to keep the whole session about the same length the long earlier 65% segment was reduced in length.

My thought was that in this session, when I reached the end of the 128% efforts, as previously my SmO2 readings would be significantly depressed. The plan was at this point to ride for 10 minutes at 100% of my FTP, with a depressed SmO2 reading. My thought was that this would provide an excellent training stimulus and that it would be interesting to see whether the SmO2 reading "recovered" significantly when I was riding at that intensity.

I was surprised by what actually happened, I naively thought that given the similarity of the loads on both occasions there would be a response which was at least similar, I was wrong!

As you can see during this second session the SmO2 levels remained constantly around the 90% mark when riding at the 65% of FTP level. When I hit the initial 100% of FTP effort at around 42 minutes the SmO2 reading remained virtually unchanged though tHb dropped as had been previously observed. The big difference came when I hit the 128% intensity efforts at around 45 minutes, there were minor (<5%) drops in the SmO2 reading which recovered quickly and fully and at the end of these efforts the SmO2 reading was still well above 85% and it remained at this level throughout the 10 minute 100% of FTP effort from 55 to 65 minutes. The data is shown below.

The stark differences in the SmO2 responses to these almost identical exercise intensities ridden approximately one week apart must have an explanation but I'm not at all sure what it is and I'd be very interested in any suggestions! Has my ability to deal with higher intensity efforts miraculously been transformed in the interim period as a result of the training I have been doing? Now that WOULD be nice!