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Development Team Member
Posts: 46

I'm new to the forum and am considering whether this technology is a route I would like to go down. I am a UK based cycling coach with a particular interest in power based training and it's application particularly in endurance events, up to and including 24hr TT races.

I have a couple of questions.

  1. Have the SmO2 readings generated by the Moxy Monitor been independently validated against the more traditional laboratory based measurement methods and if so where has this been written up/published. I'm keen to make sure that the numbers popping out of the unit are accurate, reliable, meaningful, consistent and have been independently verified.
  2. Is there a clear explanation somewhere that I can read which clarifies, for a non scientist, why the SmO2 figures fall when the load (and therefore oxygen demand) is rising. I'm thinking as a cyclist where the graphs show SmO2 rising initially as demand (wattage) rises which makes sense but I'm not clear why SmO2 falls later in the tests when wattage and therefore oxygen demand is still rising. Instinctively I'd have expected SmO2 to rise up to it's maximum and then stay there until such time as the oxygen demand (wattage) fell back again.
Many thanks.


Posts: 266
Hello Q,

1) Here is a forum thread that discusses the problem of NIRS validation a little bit.

We are also working with a university to do some comparison measurements with other NIRS devices but that won't really solve the problem of validation.

2) Some of our physiology people might jump in more on this question, but for starters, check out the "What Moxy Measures" section of "Introduction to Muscle Oxygen Monitoring with Moxy" eBook.

That can be downloaded from our Resources Page.

Moxy measures in the capillaries and tissue of the muscle where oxygen is being consumed. A simple way to think about SmO2 is as a measure of the balance between supply and demand for oxygen.  When more is demanded than is being supplied, SmO2 will go down.

Another way to think about SmO2 is that the total amount of oxygen consumed by the muscle is the blood flow through the muscle times the Arterial-Venous blood oxygenation difference.  When more oxygen is needed, either the blood flow increases or the Arterial-Venous difference gets bigger.  The arterial oxygenation often stays in the 90%+ range (except in EIAH) so to get a bigger A-V difference, the Venous oxygenation will be lower (i.e more oxygen is extracted).  This shows up as a lower SmO2.


Development Team Member
Posts: 46
Hi Roger

Thanks for that. The supply and demand explanation clicked immediately with me and the fall-off now makes sense [smile]

It seems to me that to establish the point where supply just starts to fail to meet demand using an incremental test and then to target that point using pre-programmed ergotrainer control files on my VELOtron might be  a good method of attempting to force adaptation.

Juerg Feldmann

Fortiori Design LLC
Posts: 1,530
First of all thanks  for visiting  the forum.
 Your  questions  are appreciated  and I am not sure,whether I can give you answers , who may  be helpful ,but I will try as good as possible and  other readers may  jump in a as well.

1. interest in power based training
 If you are interested in power based  training, than  you will see, that we have a fundamentally different approach.

We use  power as well, but not  to quantify the training ( load  and or recovery )  we use power  to  see, whether the physiological systems  are not  recovered  as of yet or  are  or have improved  so that by the same physiological load we see the  same,   higher or lower power output.

Depending what  workout  we did, we may have overloaded  the muscular system as one goal  and as  such we  will  not see the same power out put the following day, if we use a  %  of  for example FTP  or other   one point assessments.
 We may in this example see, that by the same  wattage the  tHb  may  not increase  as usual  due to  overload  of  the vascular system the day before.
 This   lower     ability to move blood will  contribute to a different delivery  ability of  Blood (  O2   )  and therefor  by the same wattage we  may have to find a different metabolic  way to move.
 The   lower O2  delivery    due to less blood  flow  will create the need  to   for  example  produce the needed ATP  by different metabolic  options, which may change the way   the   body reacts.
 The increase In  more glycolytic    energy  production help or the  increase In O2  independent energy  production can for example increase the  CO2  situation and as  such the O2  dissociation curve  will shift top the  right and SmO2 trend  may now  by the same load  drop instead  of being   perhaps in a balanced situation.
 Many  more  reactions can occur    as   physiological reactions  do not follow   stable wattage  rules  or loads.
 It is not the wattage  who decides the  physiological reaction  it  is the physiological reaction and ability  who decide  the   wattage  we  can  produce   an the time we can maintain this wattage.

 This is  one fundamental difference.

 Now  to your point 1

- traditional laboratory based measurement methods. 
I need some help here to   try to give a better answer.
Here a try:
 NIRS  should not be  compared  with   some of the traditional equipment's  like VO2  and  Lactate for example.
 NIRS is a direct  information form the working area  and as such   live information on what is going on.
  VO2  and lactate  are indirect methods  where we  hoped that the  information  may  reflect the situation in the working muscle's  but there is always a  time lag.
 NIRS is compared  with   invasive methods  of blood assessment  for O2   situations.As  such it is direct but  with the advantage , that it is non-invasive.

Detection of Hypoxia

at the Cellular Level

Laurie A. Loiacono, MD, FCCPa,b,c,*, David S. Shapiro, MDa,c


What is the Next Best Thing to Detection of Hypoxia at the Cellular Level?


Somewhere between direct detection of hypoxia at the cellular level (ie, bio markers,

enzyme assays, complex histopathologic analyses) and indices of global hypoperfusion

(ie, lactate, ScVO2, urine output) lies a potentially more practical and economical

method of tissue oxygenation assessment: near-infrared spectroscopy (NIRS).

NIRS is an evolving technology that uses near-infrared light to provide a continuous

assessment of regional, microvascular blood flow and is measured as the quantitative

clinical variable tissue-oxygen saturation (StO2). Biologic tissues are transparent to

light in the near-infrared spectrum, whereas oxyhemoglobin (HbO2) and deoxyhemoglobin

(Hb) have significantly different spectra56 (StO2 5 HbO2/[HbO21 Hb]). This technology

can be used invasively via transcranial or percutaneous catheters, or

noninvasively using cutaneously applied probes.

Hypoxia (n.): a deficiency in the bioavailability of oxygen to the tissues of the body


Now  here a  nice  summary  and the same is  true  to  VO2  testing , when    load  durations are too short ( BELOW 5 - 8 MIN. AND EVEN THAN The RESPIRATION SITUATION Like LOCATION  AND MORE ( IN CYCLING POSITION Change  ON The HANDLE BAR) WILL Change The Readings ON The  MOUTH , WHICH MAY NOT REFLECT  THE REACTION IN The WORKING MUSCLE.

Thirdly, an alternate or a complementary explanation to the pattern of plasma ]La-] response to ramp exercise can be suggested. According to this explanation, lactate is produced in the working muscle: (1) as soon as the exercise begins, as suggested by Brooks (1985); or (2) following a delay, according to the theory of the anaerobic threshold (Davis 1985). Under both hypotheses the onset of lactate production within the working muscles occurs at comparatively low work rates. At that time: (1) the amounts of lactate produced and the gradient between muscle [La-] and plasma [La-], and the amount of lactate released from the muscle remains small; (2) cardiac output and muscle blood flow are also low and do not favour lactate release

from the working muscles and its distribution into S; and (3) the small amounts of lactate released are diluted within the comparatively large S, thus resulting in a very small increase (if any) in plasma [La-]. Therefore,

a delay could be expected between the beginning of lactate production within the working muscles and the parabolic rise in plasma [La-] in response to ramp exercise in a similar way that, in response to a short period of severe exercise, the peak value of plasma [La-] is only observed following a several-minute delay into the recovery period (see Hirvonen et al. 1987, 1992). Consequently, plasma [La-] concentration at a given t during a ramp exercise does not reflect lactate production in the muscle at that precise t and at the

exact corresponding work rate, but at a previous t minus ~ of unknown and probably variable length, and at the corresponding work rate. This phenomenon might have been overlooked in the development of the theory

of the anaerobic threshold which implicitly assumes that plasma [La-] at a given t reflects lactate production and thus the metabolic state of the muscles at that precise t, and at the exact corresponding work rate. This is very unlikely to be the case, particularly during the exercise protocols of short duration and with steep increase in work rate used for the detection of the anaerobic threshold (Anderson and Rhodes 1989). In this type of protocol, where VO2 significantly lags behind the value expected for the corresponding

work rate (Whippet al. 1981), it may be expected that plasma [La-] also tracks the metabolic state of the working muscles with a significant delay, particularly at the beginning of exercise for the reasons presented


Are the numbers  pooping up  from lactate analyzer  true ?
 If  you compare an SRM,  Polar wattage  sensor, Cycle ops and so on, are they  equal ?

We use the same wattage info  for assessment and workouts,  so  we may have not the real true wattage perhaps,  but as long we know   we always have the same repeatable  power output  we  do not worry too much. Same is true  with NIRS.
NIRS is used  sine  a long time, but it was  simply   not easy to use  for coaches and athletes due to price  and   equipment. Now  it is affordable  and  simple to use  and  it is used in many different sports   like  ice hockey , soccer, skiing swimming cycling  and so on for  interval  workouts  to have individual  length of load  depending on goal as well as  individual recovery time  for  ) refuel ling )  as well as  individual    repetition numbers.
 It is used for  strength  workouts  as well  and for  trend information in long distance events.
Google NIRS  and you will find  endless information on the validity of this  technology  or  browse  our forum.

 Try to answer point 2

 SmO2  is a trend information   and in MOXY  the % is an absolute number, which indicates the   situation of O2  supply  and demand.
 An increase in SmO2  indicates that the % of  Hb  loaded with  O2 is increasing . (  It really is  an indication of O2  on Hb  and  Mb ) Many NIRS info  are based on   something called O2Hb  and HHb. O2 Hb  is  the wording or name  for Hb  which is loaded, versus HHb  which is the name  for Hb  which is  not loaded  with O2.
 Now here  it is  where it is getting somewhat  more complex.
  We  normally assume, that when SmO2  is increasing, that we deliver  more O2   than we  currently  utilize and as  such the O2   %  will increase indicating a situation, where O2  delivery  is  above the O2  demand. So the needed  ATP demand  to support  the  actual   wattage level is covered  with O2  plus always some O2 independent energy   metabolic  activity which never is  separated  anyway.
  So at the beginning of a  step test  we will see an initial drop of SmO2  followed by an increase in SmO2  reflecting the initial use of O2  from the storage  are    due to  lag time of  delivery systems like the cardiac output.
 Than  as  soon cardiac output and respiration pick up we have  an increase in delivery of O2     and this may be  bigger than the current need  of O2  and SmO2  will increase.There are other reactions responsible like the vascularsation reaction and  vasodilatation effect of some hormones.
col thb smo2 r leg.jpg 

The above  pic  shows  a test  from a top athlete. Green is  SmO2 trend indicating an initial drop explained  above, an increase in SmO2  due to  higher delivery than utilization, a relative balanced  intensity  due to  balanced  ability of  delivery and utilization and  at the end a drop in SmO2  as the delivery is less than the O2  demand  so SmO2  will drop.
 Brown is  an indicator of  blood flow   at the same time, with an initial increase  due to  different  reactions like CO  up and vasodilatation  followed by a balanced situatinn and  a  drop due to    higher muscular tension in a higher load which overrules the CO  and  vasodilatation effect.

- sense but I'm not clear why SmO2 falls later in the tests when wattage and therefore oxygen demand is still rising

As you point out wattage is  going up  and as  such the demand  for energy  and if possible   energy delivered  as O2. The problem is, that we  may demand  more O2    but we simply can't deliver.
 So we will try to use   O2  but if  delivery  is behind  demand  SmO2  will drop    and there is a point, where the  O2  demand is  so high , that the body can't  deliver  and a hirarchy will  kick in  on who  will have priority  for the  O2  which still can be delivered.
 The   brain ( CG  willl decide, that  certain    systems like brain itself  cardiac system  and respiratory systems  are more important  than  the legs  for  survival  and   we simply will reduce motorunit recruitment    so we  do not steel O2   from the vital organs   and we  will have  to slow  down or    simply quit moving.
 In cyclng  terms the athlete will tell : I did not had the legs  today "  , which is absolutely true but the question is  what system limited the  O2 supply to the legs. ?  Wattage will not give you any answer.
 NIRS will.  Here a very   short insight view in   how coaches  use   and  understand  MOXY  for their   workouts  and assessments. This is a part of the ME seminar  ( Moxy expert )

hope this helps a little bit to shine some lights in a  future  game changer in activity planning  and  practcial applications


Development Team Member
Posts: 46

Yes, that all makes general sense and I am in no doubt about the fact that wattage, or applied load, is not the determining factor but the result of multiple physiological delivery systems, it is the output rather then the control.

My point was to use the "state" of the muscle physiology as indicated by the Moxy data to identify what type of load (wattage) might force the muscle to work at around the point where it was being taxed in order to try to bring about adaptation.

On a practical point when you are using the unit in real time where is the Sm02 data displayed? I don't see a monitor, wrist unit or anything along those lines.



Posts: 266
Hi Q,

For data display, we rely on 3rd part applications or software.  The data is sent out using ANT+ so there are quite a number of options for this like PC based, Android phone, iPAD, and wristwatches.

The following document describes what's currently available and there are more options in the works.

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