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Development Team Member
Posts: 168
From Daniel's post re: VO2 calculations 

"The discussion on VO2 calculation is very interesting (at least for me) but would probably deserve a different topic."

Agreed. Thanks for suggesting. 

 VO2 sampling & cardiac impedence cannot be included with the MOXY 5 1 5 assessment / 4 1 4 recovery assessment or for guided workout, does anyone know if there is a reliable surrogate measure for SV ?

I have used pulse pressure method (which is a measure + some calculation) however I'm thinking applying the BP cuff compressions during the 1 min rest has some effect  that may alter the MOXY info? And the the abstracts that I have scanned show reliability is up and down depending on intended uses.  

Or is the NIRS info showing us this from the tHb trends / HR reactions on each second step ? 

Any thoughts?

Development Team Member
Posts: 264
Hi Fred,

thanks for bringing back this topic.
As shown by Juerg few times being VO2 equals to HRxSVx(A-v)O2, there are several factors that contribute to the result and NIRS can give some hints.
But I don't think it can be used as surrogate of SV.

There are a lot of articles about VO2, I found this one very interesting:

Poole DC, Barstow TJ, Gaesser GA, Willis WT, Whipp BJ. VO2slow component: physiological and functional significance. MedSci Sports Exerc

In there you can find this picture:
And there are lots of correlations with NIRS measurements.
Moderate intensity: VO2 is stable after a couple of minutes. This should correspond to STEI zone with homeostasis in SmO2 and tHB
Heavy intensity: should correspond to FEI. Homeostasis is lost but can be "recovered" 
Severe intensity:should correspond to HII. homeostasis is completely lost and the exercise will lead to exhaustion in few minutes.

In the moderate intensity region, the relationship between VO2 and Power (could be velocity for runners) is approximately linear and it is based on calculations similar to the ones I've made a couple of days ago.
Let's take the second step: 180W=180J/s pushed on the pedals.
To get that power the body consumes a lot more: supposing an efficiency factor of 0,22 it means the power produced is 180/0,22=818 J/s which is 195 kcal/s.
At this intensity (approx 55% of VO2max) RER should be in the range of 0,85 which means 4,86 kcal per liter of O2 consumed.
Put them together: VO2 (l/min)=195 (kcal/s)/4,86(kcal/L O2)*60(s/min)=2,4 L O2/min.

Probably the efficiency factor and RER to O2 consumptions need to be revised as they are athlete/tecnique specific, but that's where the quasi-linear relationship comes from.
And, from my point of view, it could be useful to better understand the NIRS measuments.


Development Team Member
Posts: 279
Daniele. Just a question. Have you done a TIP and looked where your FTP or CP lies somewhere in the Moxy "zones"?

Development Team Member
Posts: 264
Hi Ruud,
last one 10 days ago (the one I showed two days after a race).
Below the full graph:
CP is between step  5 and 6.


Development Team Member
Posts: 1,501
Great  discussion.
 Here  some   interesting add ons  and thoughts.
 1.  If you  get  an x  ray, which  can be done  since many years  you will see some interesting feedback   but not  everything.
 So  when  they   created  the MRI   we  got a  nice step forward  for more direct feedback on  what we look  for.
 So  naturally  we see more on a MRI  than on an x  ray .
 So  do we go back now  and say, well  we  can not see this problem on an  x ray  but only on an  MRI  so therefor the MRI  is not validated  ???
  Now  when we look  how NIRS is treated. We  have a  direct  feedback  so much more  direct information than  form a  VO2  grate idea  or  test but a  very in direct  feedback  with many  areas where we may loose.

So we look h what  VO2  is  doing r lactate  and than   look  what NIRS  tells  us  and tan  go back  and argue  that we  see or not see this  in   the classical tools.
 So  there  are many other areas. , where NIRS  can give some new  insight. Here  another one  where VO2  is sued but if you us e  a few  MOXY's  you can see why we discuss the slow VO2  component.  .Hope you can make the connections.

Am J Physiol Regul Integr Comp Physiol. 2007 Aug;293(2):R812-20. Epub 2007 Apr 25.

Thigh muscle activation distribution and pulmonary VO2 kinetics during moderate, heavy, and very heavy intensity cycling exercise in humans.

Endo MY1, Kobayakawa M, Kinugasa R, Kuno S, Akima H, Rossiter HB, Miura A, Fukuba Y.

Author information

  • 1Department of Exercise Science and Physiology, School of Health Sciences, Prefectural University of Hiroshima, 1-1-71, Ujina-higashi, Minami-ku, Hiroshima 734-8558, Japan.


The mechanisms underlying the oxygen uptake (Vo(2)) slow component during supra-lactate threshold (supra-LT) exercise are poorly understood. Evidence suggests that the Vo(2) slow component may be caused by progressive muscle recruitment during exercise. We therefore examined whether leg muscle activation patterns [from the transverse relaxation time (T2) of magnetic resonance images] were associated with supra-LT Vo(2) kinetic parameters. Eleven subjects performed 6-min cycle ergometry at moderate (80% LT), heavy (70% between LT and critical power; CP), and very heavy (7% above CP) intensities with breath-by-breath pulmonary Vo(2) measurement. T2 in 10 leg muscles was evaluated at rest and after 3 and 6 min of exercise. During moderate exercise, nine muscles achieved a steady-state T2 by 3 min; only in the vastus medialis did T2 increase further after 6 min. During heavy exercise, T2 in the entire vastus group increased between minutes 3 and 6, and additional increases in T2 were seen in adductor magnus and gracilis during this period of very heavy exercise. The Vo(2) slow component increased with increasing exercise intensity (being functionally zero during moderate exercise). The distribution of T2 was more diverse as supra-LT exercise progressed: T2 variance (ms) increased from 3.6 +/- 0.2 to 6.5 +/- 1.7 between 3 and 6 min of heavy exercise and from 5.5 +/- 0.8 to 12.3 +/- 5.4 in very heavy exercise (rest = 3.1 +/- 0.6). The T2 distribution was significantly correlated with the magnitude of the Vo(2) slow component (P < 0.05). These data are consistent with the notion that the Vo(2) slow component is an expression of progressive muscle recruitment during supra-LT exercise



Development Team Member
Posts: 279
OK. I asked because I thought its maybe nice to get some grasp of your levels based on CP and Moxy (STEI, etc) combined to see any relation between them (or not). In a sense I would think an O2HB dropping continuously above CP (VO2 slow component) and stable at CP. But I think we can only see that in an exercise for like 20 min ar CP and 20 min slightly above CP (say 5%). Maybe a nice one to do Daniele over coming weeks? I will do that one as well then [smile] Maybe we should agree on the same warmup protocol as well. Maybe start with 3 min sitting on the bike (no pedalling) for calibration and then warmup for 10 mins (we should determine how, with a ramp or ....)

Development Team Member
Posts: 1,501
Will be  fun to see  as we  did this often.  3 min calibration is  great  idea  and look  the foot pedal position  so you have the same leg in the same  position  like 12.00 clock  for example  or  make a decision or  write it down.
 Warm up protocol.
 Do  5 min steps  like in a 5/1/5    and make the one min  rest. Start  by 50  %  of your   estimated  CP  and than  go   after 5 min  1 min break  to  70 %   same  than to  90 %  same  and than  hit CP. Do  CP  for  20 min... Than  go back  and do a reverse  5 1  step  so go back to  90 %  and  than  70 %  and than  50 %  as   in the warm up  just the opposite.
If you can  take  HR  and if you have  a chance RF.

Development Team Member
Posts: 94
NIRS avo2diff.jpg 

Muscle oxygenation trends during constant work rate cycle exercise in men and women


1) if you take blood hemoglobin in grams per liter
2) if we know how much O2 is required for the respiratory musculature, myocardium at different loads and as a constant intake for internal organs
3) We make the assumption that with some amendment Smo2 reflects the arteriovenous difference, although not all researchers find such a correlation.

Further, from the calculation of 1 liter of O2 = 75-80 watts, calculate the O2 intake by muscles, and calculate the Q and SV at the heart rate.

Verification according to PhysioFlow data




Development Team Member
Posts: 94
Of course, the formula should be made better, it's just an example for illustrating. Need Thb correction

Attached Files
xls SV_SMO2.xls (15.50 KB, 9 views)

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