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Development Team Member
Posts: 1,501
I am  for the moment flooded  with  emails  asking about feed backs on SmO2  numbers.
  There are some misconceptions on  situations, where we  see a  very low  SmO2  number in athletes but they  perfectly well still move nicely  yes, it is  work but not  c so that they have to quite  despite a very low SmO2  number. I like to show an  assessment  done  and discussed on here  before  from Ruud  2  assessments , one  somewhat  " fatigued " or  what ever that means  and one more recovered.

smo2  both  all 2 weeks  apart.jpg

You can see  towards the end of  both assessments  very low SmO2 values but he still was able to  push  2  x 5 min  so  it is not a  very high load  compared what he for sure  can push if going 30 seconds all out.

a) a flat SmO2  no matter  what ever level  indicates  first and foremost a balanced  O2  intake  and utilization situation. In fact we discussed this before  it may even mean  that despite a higher intensity  he may  use less O2. That feedback is given over the closer look  of tHb  trends  and O2Hb  and HHb biased or  direct  as Daniele  once showed nicely.
 So here  a closer look to  illustrate this  from the  darker green  test in a  recovered  stage  of Ruud.

thb smo2  last 2  steps.jpg 

As you  can see  SmO2 very flat indicating a  potential balance in intake  and  utilization. Now  tHb trend is increasing indicating a  closer look is needed to see,whether the compensation of delivery is  strong enough to   either maintain SmO2  balance,  or  slightly actually increase O2  as  he may have  not pushed  as hard  anymore  or  perhaps  still slightly dropping as the compensation is not good enough to maintain balance. So let,s look at  O2HB  and HHb trend ( keep in mind  that  Mb is involved as well.)

bias late 2.jpg 

You decide ?

 Now  NIRS limitation.
 This information above  are  form one single  muscle the VL. He is  an important  one in cycling but not the only one.
 The fundamental difference  we  see in  Pro cyclists versus very great  amateur  cyclists  versus  some of us  is  in many cases  not  at all VO2  max  alone. Not even  level of lactate  or  HR  max values.  It is efficiency in the  systems  so  how efficient is the cardiac system  or the respiratory systems  or the inert   and intra muscular  coordination ability.
All this above factors can be,  but not have to be, stimulated  by high intensity . In fact many  of them  may not react very well on high intensity as they simply  try to survive  and not to improve  at all.

Here a  very  small back up on this statement.
This is a reason  why I  give ideas on MOXY placement   to better  stay on a muscle sling  or chain  instead of  bothering  with left and right.

Med Sci Sports Exerc. 2009 Jun;41(6):1277-86. doi: 10.1249/MSS.0b013e31819825f8.

Changes of pedaling technique and muscle coordination during an exhaustive exercise.

Dorel S1, Drouet JM, Couturier A, Champoux Y, Hug F.

Author information

  • 1Research Mission, Laboratory of Biomechanics and Physiology, National Institute for Sports (INSEP), Paris, France.



Alterations of the mechanical patterns during an exhaustive pedaling exercise have been previously shown. We designed the present study to test the hypothesis that these alterations in the biomechanics of pedaling, which occur during exhaustive exercise, are linked to changes in the activity patterns of lower limb muscles.


Ten well-trained cyclists were tested during a limited time to exhaustion, performing 80% of maximal power tolerated. Pedal force components were measured continuously using instrumented pedals and were synchronized with surface EMG signals measured in 10 lower limb muscles.


The results confirmed most of the alterations of the mechanical patterns previously described in the literature. The magnitude of the root mean squared of the EMG during the complete cycle (RMScycle) for tibialis anterior and gastrocnemius medialis decreased significantly (P < 0.05) from 85% and 75% of Tlim, respectively. A higher RMScycle was obtained for gluteus maximus (P < 0.01) and biceps femoris (P < 0.05) from 75% of Tlim. The k values that resulted from the cross-correlation technique indicated that the activities of six muscles (gastrocnemius medialis, gastrocnemius lateralis, tibialis anterior, vastus lateralis, vastus medialis, and rectus femoris) were shifted forward in the cycle at the end of the exercise.


The large increases in activity for gluteus maximus and biceps femoris, which are in accordance with the increase in force production during the propulsive phase, could be considered as instinctive coordination strategies that compensate for potential fatigue and loss of force of the knee extensors (i.e., vastus lateralis and vastus medialis) by a higher moment of the hip extensors.



Development Team Member
Posts: 1,501
Now here a  second  answer on the SmO2  question I  gave  as a discussion point or some thoughts on  another  website  forum.

  • I have series of emails concerning some questions to this topic I just like to make a short comment on here agreeing with Adams points.
    see above Adams great point
    “My personal thoughts on this, from my research and logic, is reaching 0% muscle oxygenation is impossible from a healthy, alive person, that isn’t purposely cutting off blood flow, to the point of damage. So, just think about that, when setting your range expectations”

so his other point he makes on NIRS info:

” So, the BSXinsight Gen2 SmO2 is calibrated for absolute measurements within a range from 0% to 100%, where 0% indicates that all hemoglobin in the tissue volume directly below the sensor have completely given out their oxygen and, thus, consist of deoxyhemoglobin, while 100% indicates that all hemoglobin in the tissue directly below the sensor are oxygenated (oxyhemoglobin). ”

is somewhat in a contradiction. I do not know how BSX exactly works but all other NIRS equipment when they show low or zero clearly do not have zero O2Hb. a low number simply means allow pO2 pressure as well a limitation from the technology. . Remember NIRS does not make a difference between Mb and Hb O2 loading so unlikely is zero a zero value but a limitation of the ability to read very low levels of O2 on Hb and or Mb. It is less a personal believe but a fact based on some great studies and research . Here a very short part of one of the leading groups on this.

“Richardson et al have concluded that: ‘‘…intracellular pO2 remains constant during graded incremental exercise in humans (50–100% of muscle VO2max)’’ so that: ‘‘With respect to the concept of the ‘‘anaerobic’’ threshold, these data demonstrate that, during incremental exercise, skeletal muscle cells do not become anaerobic as lactate levels suddenly rise, as intracellular pO2 is well preserved at a constant level, even at maximal exercise’’ (p. 63168). They also conclude that: ‘‘Net blood lactate efflux was unrelated to intracellular pO2 across the range of incremental exercise to
exhaustion’’ but was ‘‘linearly related to O2 consumption’’ (p. 62768). Another study confirmed these conclusions: ‘‘…consequently these data again demonstrate that, as assessed by cytosolic oxygenation state (deoxy-Mb) during incremental exercise, skeletal muscle cells do not become ‘‘anaerobic’’ as lactate levels rise, because intracellular PO2 is well preserved
at a low but constant level even at maximal exercise’’”

Now as Adam showed nicely with a occlusion test the values in BSX drop down to very low levels indicating , which is not surprising that they use a NIRS technology.

So as he points out

” So, just think about that, when setting your range expectations.”
But you have to understand, if we fudged the numbers to make them look better, those who rightfully want to see absolute, would be very disappointed..

Absolutely agree and great point made and it is important for newcomer in this bio feedback ideas to get some pointer in this directions. So I like to make a super simplistic feedback on here to show you what you or when you can expect some lower or less lower numbers.

A artificial occlusion test is really a “forced” delivery problem.
meaning , that I stop O2 delivery to the working or O2 needed area and as such the cells in this are will have to take on what is already there.. So that is what D Adam explains nicely the O2 need of any cell and the reason why we see SmO2 dropping to a very low even zero level depending how the NIRS can get absorb or reflect. I will show a nice occlusion test with BSX and MOXY at the end done on the same muscle so all the same conditions and it shows NIRS works nicely no matter on the name or brand.

Now in a 6 min occlusion test, which is what is done during research due to risks involved we can assume if the occlusion is properly done, that we have very to no O2 inflow and we use from Mb and HB O2 as long as possible. Now the fun part is that we do nothing and have no blood flow. so we are basically on a resting metabolic energy consumption. Now there are nice formulas under occlusion, where we can calculated the amount of energy or O2 used..
In this simplistic case, we assume the whole body is under occlusion so we have no O2 supply anymore.
Resting metabolic rate may be 1800 kcal/ 24 hours so we have 75 kcal / h or during occlusion situation of 6 min we use about 7.5kcal /h.
No NIRS equipment will show very low levels of SmO2 as shown in occlusion tests.

Now we do an activity . first . . If we increase the load slowly we give the delivery systems time to react to the O2 demand and as such many will be surprised, that in a VO2 max test or a 3 min LT step test the SmO2 values do not go very low depending on limiter and or compensators.

But if you do a Wingate test you will see a similar low level like in a occlusion test. This is for many surprising as a wingate is a typical classical anaerobic assessment but with NIRS it shows , that O2 use is higher per time in a Wingate than in a VO2 test. For all the great critics on here, there are many publications in accepted papers who show this results.

So lets go back to why we can see very low levels in NIRS assisted workouts.

Let’s do a ride and push a short hill up all out for 30 seconds.. You go to the base of the hill with a HR of 120 as SV of 120 so CO of 14.4 L / min
So approximately 3 x higher than in your resting occlusion test where you may had a HR of 60 and a SV of 80
Now at rest in the occlusion situation your capillarisation is relative sleepy and you just move the O2 needed to keep every body happy in the tested area which may be 50 – 70 % of SmO2 values
In the beginning of the hill situation you will have in most cases a much higher SmO2 so the resting SmO2 will increase..
The highest values you may see are depending on the equipment somewhere between 90 – 95 %( There are many factors who avoid 100 % readings.

Now you push up the hill suddenly so delivery system will be surprised and you create a natural delivery problem which is close to the artificial occlusion created delivery problem.
Now 30 seconds all out . Your working metabolic rate in a 1 hours all out can easy be 1800 kcal / h ( and that is NOT all out ) so 1800 in 60 min will give you 30 kcal in 1 min or in 6 seconds , the duration of the occlusion we are down to 5 kcal
This moves us relative close to the same situation a sin an occlusion test and that’s’ why when we use NIRS we can see tsi very low numbers in a workout depending what wee do. There are than some other very intriguing options left for the body to react.
So to support Adams point
“So, just think about that, when setting your range expectations.” ” if we fudged the numbers to make them look better, those who rightfully want to see absolute, would be very disappointed.

Adam great points and absolutely agree. And here for all NIRS sceptics a occlusion test sent to us from a MOXY and BSX user Thanks so much

 Here the  BSX  MOXY occlusion tests   from a biceps .  sent to us  by Ruud.
occ smo2  BSX  MOXY.jpg   You  can see very similar trend  with a  small  difference by 360 +-. Now  to se why we  would have this SmO2 trend  you have to go back  and  look at  Occlusion quality  as it is not easy  with a  simple  elastic  to create a  perfect occlusion. So here some brain work.  Do you remember how you increase oxygenation in the brain ?
Okay, try to imagine you make an occlusion test. You pull  to close  blood flow  as good and as  fast and as hard as possible.
 In case you do not immediately create  an arterial occlusion, what  would you expect to see in tHb reactions ?
 Now  in case the pressure before the band  is increasing as well , what risk do we have may happened towards the end of the 6 min ? Now  if you identify thee risk  correctly what  tHb  reaction  would we  expect  to see ? Have  fun   And here  to avoid the questions I  already get.
 Proof  of  wingate  going lower than  VO2  max test.  ( accepted papers  not biased  from me )

deoxy N.jpg 

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