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Sorry Ruud   , but  there is  some more  information on lactate and NIRS  and  why it  can be used  in combination and  where  or why it is  much more questionable to be used in combination. But it is  as well a  respond  to an increasing numbers  of test I  get mailed to me, where people  use their lactate  equipment and combine it  with  NIRS.

I  will show some examples  from contributor in this forum  and some from outside  contributor.

 It is  very easy to understand  why we hope  or better hoped , that  NIRS  can give us lactate feedback.
 You can go back more than 10 years, where this was a  common hope including  for  us but  once we started to look at   the both ideas we had  to accept  that they   yes look at  metabolic  changes  during  an activity but in a very different easy.
 But one of the biggest  fun  part was, that we already had some  discussion  with  lactate  as  the original idea, why we  where testing  for "lactic acid " was the bad reputation  we forced  upon this substance.
 So  lactate is the reason  for fatigue ,for  failure for  muscle soreness or what ever we  got educated  on.We  have to avoid  it have  to learn to tolerate it  and have to get rid of it as fast as possible.

The problem  was or is:
 In any  lactate  finger testing or ear, we have a value  where we have more questions  than actually a direction or answer.

We have no  clue on where it was  produced, how much was  produced, how much  do we  get in our sample, how much was recycled  before the blood reached  the finger, how  fast  does it disappear , what causes  different   speed  of disappearance  and so on.

But the main reasons really was  to find out  the intensity , where we  have a good  option to go very long.  let's  name it aerobic or   oxygenation intensity , so an intensity where e  have no  problem  to create  the  ATP  security  by delivering  steady O2   and in an amount, that we can nicely upkeep ATP  levels, in fact we  even can afford to do  additional  activities like talking  as we have  far enough  O2  delivery  that we   can afford   given out  unused  or nor delivered  O2  deep  enough into the lungs.

Than we  where hoping to find  that  nice  balance  so we   where able to  maintain  performance as  delivery and utilization of O2  was  perfect and ATP levels  ware save.

And last but not least  an intensity, where we  feel or   had  the  information, that   we can not  very long sustain, as  O2  delivery was  lower than the O2 needed  for the activity including maintaining pO2  pressure in vital systems  and   keep ATP level in a  needed  level.
 The result of this mismatch  of O2  delivery and O2  utilization   than leads  to a  slow down of performance  due to  survival   security  for vital systems    and   ultimately  ATP levels.

The  solution is relative simple. Get rid  of  O2  demanders  or  users  , who are ultimately not needed  for    survival  and  that's  where loco motor  muscles  come in  and the  often discussed   metabolic pyramid.
  Now  why this story.

Main reason is a  question I will answer on a different thread.
 But here first our  dilemma.

In the past  we  ad  VO2  and lactate  and  not  that easy  for   average  daily users  to   have non stop feedback  from this  equipment. So we needed something  and we  developed test.
 Lab settings  with specific guidelines  but  85 %  +-  of the variables, the physiological systems     where not  that  easy to control.
 Nevertheless  we  made  big story  out  of room temperature,  humidity,  day time  an much more  as they  for sure all influence  physiological reactions. 
 But we needed  up  with  1 point  we search in a  test   like VO2  max . Max  HR, LT 2   VT  and so on.  and  form than on we where  sure we had  the  gospel  and  where able to   create calculated  programs. There is or was  another  very important  factor.
Impression. If  we tell people  we  will take blood and have gloves on and it looks  very scientific , the test sells much better.
 If  you add a mask  and  some  bigger  equipment with sound  and graphs  and  you are even  more impressed.
 How  can we  just fix  a  small device on a leg and  arm  yo barely see it  you  forget  that it is there as you test  and assume it is as  accurad or  close  to as  accurad  as the   other ideas we used.?

Now  this  than leads  to Zoning ideas, where   when we go back in history started with the  three  explained above , but than we  every new  publication and to make a difference we  started  to add 4  5  and  more  zones into  the idea.

Than we used  performance or HR as they are easy to use  to  believe, that we  will be in the  target  zone  when we   use this feedback.
 We all know  it can be true  but as well we can be  off. and HR is  an example  wattage users  like to   throw into the discussion.    As  much HR  can be off  due to  different factors like heat,  as one example  so  can be wattage off ( true  still the  same objective  load,  but  very different physiological  contributor   or we may not even be able  to   reach this   wattage ) out   of the same reason   in heat. Physiological change in  survival mode  so  core temperature is  the priority over  performance   and  HR as a  part of CO is needed to   control the  proper  Core temperature and therefor  less blood is  available  and with it O2   for  the same performance we  may had in a  test a few days  back.

Where does  that leads  us.
 Well we need a  direct live feedback  and we  can get rid  of all this  speculation as we see what is going on instead of  speculating  what may  go on.

This leads  to  some graphs for your own thinking.

smo2  tHb  lac all.jpg 
Above is NOT a 5/1/5  it is a  three minute step test  with stops   of  1 min  to take lactate  so each lactate  number  is from a different load 250 watt start.
 So it is   basically a  classical   step test with lactate to  look for  a lactate curve.

Now  blend out the NIRS data  above and move back  to the classical  idea  below

lac  3 min trend.jpg 

Where is  the LT ??. Now  blend  back  and forget the LT here and  think  physiologically  through  each of the steps  above  and think  what SmO2 trend  may  actually tell you.

Noe  below  some lactate " curves"  we have  from 2  of Stuarts   athletes.

a. Sharon.
lac  from 5 1 5.jpg

ou can nicely see that  the time  we offer  for  her  physiological systems   change the  trend in lactate by the  same wattage ( wattage on the  bottom axis)

Now look again the live feedback    with  SmO2 trend  and here to  show it easier I use  O2Hb  in red.

bias  RVL.jpg 
Can you see what  mean    with live feedback.  If  Sharon  as a live feedback  than  she  would not be  thinking after the first 5 min  with a lactate level  of more than 1 mmol increase  , that she  reached  her  LT 2 ???
In fact she reaches  another Lt  2  in the next  step and again one in the lats step.  More than 1 mmol increase  form one step to the other ???  With a live feedback she had  the   nice  information, that, yes  she  had  to dig into her bank account initially   or  every  time she starts new  to maintain ATP levels  but than  she  decided  to  get  some  supply to avoid a   drop  into a deficit.  Physiological systems  do not run into an O2  deficit  and if  they  do  the  are dead.( Heart attack / Stroke  to name some extreme  situation , where O2  supply  was stopped and we  reached a deficit.)

Below  another   lactate sampling  from Stuart  ( Allan )

lac  from 5 1 5 male stuart.jpg 

Now imagine the SmO2  or  O2Hb trend in this case ?

And below  as a repeat  but to keep them together  Sharon again  with some  questions.

lactate  ftp.jpg 

LT  2   where?  FTP  is above   What do we  do with all this confusion. Would it be not much easier to   help Sharon  with a love feedback  for  the goals  we may set for  her instead of  hoping  every day  that one of  the magical test results  will actually  be  as well the  proper   physiological intensity on   any  common day.?  Have fun  thinking through this mess.

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