Thinking About a Moxy Muscle Oxygen Sensor

Moxy MonitorI was recently telling my physical therapist that my BSX Insight had shipped and that I was excited to be doing tests of my lactate threshold– and his coworker asked me if it was the same as the Moxy muscle oxygen sensor.  I told him that, while they both look at blood oxygen, they get different data– the Moxy is a realtime measurement device while the BSX Insight uses a test to find a single number (the ever-critical lactate threshold).  Apparently, a rival team to mine across town uses the Moxy extensively.  Then this weekend another friend pointed me to Richard Wharton’s blog outlining how he uses the Moxy and I was just blown away.  I may have to start saving my pennies to pick up one of these things.For those of you who don’t know, Richard Wharton is a pioneer in the areas of power meters.  Back in the late 1990s (yes, over 15 years ago), I bought one of the first Tune PowerTap hubs.  In those early days, I had little idea about how to use the data from this miraculous device– but Richard Wharton was already there with tons of ideas.  He was one of the first people I know to come up with the metrics “watts per kilogram” that gave every cyclist (big and small) a common yardstick to assess cycling ability.  Although I’m sure he won’t remember it, Richard and I spoke a few times on the phone about using a power meter in those early days.  While I’ve come far, I’m my mind Richard is one of the true wizards in this area.  We all know that now that Richard was spot on from the beginning– the power meter has become such as essential part of our sport that it’s impossible for many of us to imagine training without it.

So it shouldn’t be surprising that, when Richard becomes excited about a new technology that again revolutionizes the sport, my ears perk up.  Nothing I write can do justice to what Richard writes.  All I can suggest is to do what I do:

  1. go to his blog (
  2. print out the articles on the Moxy for yourself
  3. staple them and read them
  4. then read them again
  5. and read them again

Why should you get excited about this technology?  To answer that, let me ask you a few questions first.  Have you ever hit a training plateau where you keep working but don’t seem to be getting better?  Or have you ever done a workout and wondered why you bottomed out for no apparent reason– just to chalk it up to you “having a lousy day.”  Conversely, have you ever had miraculous workouts where you saw big gains– but wondered why you couldn’t repeat them the next year? If so, then maybe you’re wasting a lot of your training time without a Moxy.

A Moxy measures blood oxygen saturation and total hemoglobin at the muscular level.  If you’re a mountain climber, you’ve probably seen (and used) a fingertip blood oxygen meter.  It’s a cheap and simple device that measures how much oxygen is in your blood.  This is roughly the same idea.  This is also the reason my initial reaction was “meh” when I heard about the Moxy as my blood oxygen at my fingertip never really changed that much when I was working out.  While the Moxy measures it directly on your leg, my reaction was again “meh” as it would only tell me how much my vastus medialis (or whichever other leg muscle I put it up against) was working and wouldn’t give me useful data unless I wanted a grotesquely huge VMO.  In other words, I was concerned that, even if the Moxy could tell me what was going on in a particular muscle, it couldn’t give me a complete picture of what my legs as a whole– or my body for that matter– was going through.  With all of these concerns– and given the high price tag of about $1,000– it was pretty hard to justify spending money on “meh”.

Fortunately, Richard was a lot more open-minded about the Moxy and proved my disbelief completely and utterly wrong.  Here’s a quick review of some the key points Richard makes– with links to the relevant content.  Again, you’ll want to read this stuff in full, but here’s an appetizer to tease the senses.

  • Usefulness of Oxygen Saturation and Total Hemoglobin.  First off, the comparison between a Moxy and an inexpensive fingertip blood oxygen meter isn’t much of a comparison at all.  The fingertip sensor gives you only a rough estimate based on arterial blood circulation.  Much more interesting, however, is what’s happening inside the muscle.  Richard makes the comparison between volts and amperes when describing the role of oxygen saturation and total hemoglobin (recall that watts is amps times volts), but I think a little more introduction is needed.  Total hemoglobin measures how much hemoglobin has perfused a region of muscle.  As you warm up, your blood vessels dilate to carry more blood.  Obviously, the more blood your muscles have, the better.  Thus, you can think of total hemoglobin as measuring how much your muscles have “opened up” and are ready to take in lots of blood (and accompanying nutrients and oxygen).  But having all the blood in the world isn’t going to do much good if that blood isn’t full of oxygen.  Thus, the other critical part of the equation– oxygen saturation– reflects how pumped up that blood is with nice fresh oxygen for your muscles to use.  Obviously, the whole point to interval training or a good warmup is to maximize both of these factors– and the Moxy is the only way that you can really tell if your body is really ready.
  • Warming Up and Nutrition.  Apparently, most of us suck at warming up– and a Moxy can show it in startling detail.  You may feel great and all ready to go, but until you’ve properly warmed up and done a few sprints, muscle oxygen and hemoglobin levels are basically asleep.  And without those levels being up there, your watts won’t ever be close to where they can be.  Even if you could muscle through a workout, a Moxy may reveal exactly where your poor nutrition caught up with you– and show you how you’re recovering and ready to go again.  This is critical information as it explains how to do things better the next time.
  • What are You Building?  Really?  A Moxy can give you better insight into whether your training is really building exactly what you want to be building.  Even if you use a power meter and a heart rate monitor religiously, most of us have only the faintest ideas if our workouts are really delivering the results we want.  For instance, we think we are improving monocarboxylate transporters when riding at 20% above FTP, but are we really?  Maybe, but it also depends on what’s happening with blood oxygen.  After all, if the cells aren’t metabolizing enough (shown by a lowered blood oxygenation), we’re just wasting our time.
  • Finding the Perfect Intensity.  One of the cool things is that you can use a Moxy in realtime with applications like Perf Pro Studio— the same application that my cycling studio (and a bunch of others) use for their classes.  If you know your maximum total hemoglobin (THB), you can go into an interval set and increase your FTP until you see a spike in your THB during your recovery to know that you’ve hit pay dirt.
  • Is Your FTP Data Out of Date?  Similarly, looking at blood oxygen saturation can give you an idea whether it’s time to retest FTP.  All you have to do is look at your blood oxygen saturation level over a set of intervals and if they are spot on consistent, it’s probably time to bounce up your FTP.  This last element is critical because most of us test our FTP in the most subjective way possible– a 20 or 30 minute stress test.  The problem is that this test reveals more about one’s pain threshold and mental fatigue than it does about one’s body.  Of course, this is where something like a BSX Insight comes in handy.

We are really just at the beginning of understanding how a Moxy can revolutionize training.  I firmly believe that all of us have so much more potential than we actually realize– it’s just that some athletes are lucky enough to find the right combination of factors (such as intensity and duration) to really improve their physiology and become great.  Tools like the Moxy may be one step to eliminating the guesswork.

Thanks for reading and be sure to like the Athletic Time Machine Facebook page and follow us on Twitter @AthTimeMachine.  If you found this post useful, please reblog it on WordPress, share it on Facebook, or retweet it on Twitter to share it with your friends.



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