SMO2 Readings and Interpretations

Background: 38M, Cat 1 XC MTB, U.S.A. Been riding 8 years and lifelong athlete (collegiate soccer)

I have access to Lactate testing and Moxy. My last lactate test was in Oct 2020. 161 HR Balance point and 264 BP watts.

I think I understand how to interpret the Moxy 5 1 5 test. I did alter the test a bit and did double intervals after 150 watts. You look for the SMo2 trend during the work stages and then identify the wattage where the SMo2 starts to decline.

SO based on this test below, how would we interpret LT1 and LBP. I did stop at 325 watts because of time not because of failure.


Hi @jimmybourisaw welcome to the FTL forum! so happy you joined.

Can you send me the actual fit file including hr, power and smo2 if possible so I can put in my software.

I will be able to respond to this no later than Sunday.

Happy to see you reply first. Send you the PM with the file. Much appreciated.

EDIT: I will add some more context of training the last year since we have worked together before. Pretty much all my training has been 200-225 watts during the week and then 3.5-4hour 165-185 avg watt rides. I did a little intensity prior to race reason but really let the 3 races so far this year be the intensity. I have 1 DNF (crash) - my fault, 1 overall win and 1 short track where I got dropped 6th perhaps (ate a big meal before the race and felt it bad). Overall been super busy with work and just took a full week off for the first time since last November.

Hello @jimmybourisaw just working on the graph.

Having to do a few fixes to my software since we have it online now, should be done today.

The detail in isn’t good enough for this king of stuff, only for longer intervals and trends.

Back to you soon.

I take it you are still not using a smart trainer correct?

Correct, this was done on rollers.

What date did you do this on so I can find in intervals

July 22 is when it was done


Ok … this is the best I can do with the test being done on rollers, and the cadence slowly dropping and then rising mid test.

As you are aware the moxy is very accurate to change. To really pinpoint everything for you I would need cadence to be very tight within 5c and stable or gradually building.

A smart training is ideal for this test to really nail things down.

However here we go!

Best I can do for LT1 is 200-225w, just due to the test being done on rollers. I think this is good enough for you for training purposes. If you want more accuracy then I would say smart trainer, sorry.

LBP is easier.

When you move from increasing oxygenation during work, to decreasing during work, this would be extremely close to LBP.

If you want to get this even closer try.

gradual warm-up to 245 watts - spend 8m there.

0w 1 minute

250w 8m

0w 1 minute

255w 8m

0w 1 minute

260w 8m

0w 1 minute

265w 8m

0w 1 minute.

When you do the above, try and keep the cadence as close as possible, within 5c at least.

Let me know if you have any questions.


ps…I know why I was having trouble with the file. The laps included the work and the recovery 1m, it is key to look at only the work, and the response to ZERO work or 1 minute recovery.


Thanks Steve. Sorry had a bit of health scare that I think I am over the hump now. Had about 3 weeks of very little training since this test. Will give this a go when I get back to full steam.

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@jimmybourisaw ok really hope everything is ok.

Send me a message when you are back on track and we will go through this.

Warning: I’ve been down a rabbit hole…

@steveneal I’ve been reading some about using SmO2 to determine critical power or velocity. My interpretation of these assessments is that the authors are using the same trend you are using above to locate LBP to identify critical power?

A negative %SmO2 slope was evident during severe-domain exercise but was positive during exercise below critical power (CP) at both muscle sites.

I’ve requested this article, but have not heard back from the authors yet. The principle author has a webinar in the Moxy learning series. He worked with Nike on the breaking two project if I remember right.

Andri Feldmann says something similar:

…if SmO2 accurately reflects oxygen supply and demand, an assessment of changing SmO2 slopes could represent CP. Specifically, SmO2 at CP must remain constant to represent the steady-state; as is seen in the exploratory data presented. While this is perhaps somewhat pedestrian, of greater interest may be the fact that, when considering in terms of CO, a greater muscle deoxygenated steady state, is correlated to a higher CP.


Are you referring to Dr Philip Skiba?


I can’t wait until you get down the ThB rabbit hole :slight_smile:

Have fun.


My off the cuff, back of the napkins, gut feel, whatever you want to call it…

If CP can be held for 30-40 minutes.
That likely won’t occur in a steady state.
Likely not a HR steady state, neither lactate, nor SMO2.

Now looking at FTP. The durations on this tend to be longer, many site 40-60min up to 70 minutes as a range.
As duration extends we have a better chance at finding a steady state.
But my thought is that the fatiguing nature of FTP work would be dragging SMO2 down.

If we add ThB to the picture… if SMO2 is level but ThB is increasing is that still in a steady state?

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Oddly enough during a zoom call with Phil about something else, I had my software open with a moxy test on the screen. About 40m into the call he asked me what was on the screen. We discussed what their was and he said it was amazing how I could find AeT with the moxy, he had never done that.

What he was doing was basically finding the peak point before the smo2 starts to show negative slope (which to me is lactate balance point) made for a wonderful discussion.



Ha! That’s awesome. It seems like combining a 5 min step test to like 75/80% of ftp then doing 5/1 at smaller (10/15 watt) increments above the find LBP would work good? Isn’t it easier to find AeT using continuous effort?

Thanks for the reply!

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The guy is Brett Kirby.

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Yes to the 515 and you can likely even do 414

You can find AeT in the step test no problem at all.

Yeah, I’ve been playing with a warm up that includes steps up to like 75% then some short accelerations with super easy rest between. This helps build SmO2 and allows me to pinpoint AeT so (in the future) if I want to work there I can. Have you seen Andri talk about finding FatMax using the NIRS?


Sure have…do you know who Andri is by chance?


Below is a pic of me doing 3 easy step sessions in a row. Not on a bicycle just on an airdyne to move before dinner.

Each step was the same increase of load each time. Note the difference in heart rate and smo2 ( I graphed as % of max so it could be relative ) - I did a third one and a little section of 8s ON / 12s OFF (not shown).

During the two-step tests first one was consistent, second one was 1m ON / 30s static rest.

The higher the smo2 the lower the RPE at the same level.

Not sure you have noticed a similarity in RPE and smo2 levels but I sure do.

avg heart rate for step in red as % max / blue is smo2 %

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