Muscle Oxygen Saturation (SmO2) with Roger Schmitz | EP#85

Roger Schmitz of Moxy, discusses next-generation physiological measurements for endurance athletes: muscle oxygen saturation, SmO2. This can already be done today at testing facilities or day to day in all training sessions, with the small and handy Moxy device.

• Why measuring SmO2 to establish training zones and use in real-time is physiologically the most direct way to know what's happening in your body at different intensities any given day
• How using SmO2 and Moxy is different from traditional lactate testing or metabolic testing
• How using the Moxy device has helped athletes massively increase the number of intervals they can do in high-intensity workouts
• Measuring SmO2 to determine your exact your physiological limiters - oxygen delivery, utilisation or even cardiac or respiratory function

04:52 -

• Co-founder and CEO of Moxy Monitor
• Holds a Bachelor of Science in Mechanical Engineering from Iowa State University
• Lives in Hutchinson, MN.
• A long background in technology development in automated machinery and medical devices as lead design engineer.
• Together with his co-founders at Moxy, they started development in 2010 and launched in 2013.
• Today Moxy is the only company that develops a device that endurance athletes can use to get real-time feedback on what’s happening in there body with their physiology.

07:45 -

• Moxy is a muscle oxygen monitor. It measures the percentage of haemoglobin and myoglobin that’s carrying oxygen in the capillaries and in the tissues of the muscle where the oxygen is being consumed.
• By measuring that, we can get an indication of the balance between supply and demand of oxygen in the muscle. We do this while the athlete is actually performing their sport.

08:36 -

• The device is a small, wearable device. It’s completely wireless. You wear it over a large working muscle. For a cyclist or a runner, that would be the vastus lateralis which is one of the four muscles of the quadriceps.
• Runners may also wear it on the hamstrings or on the calves. For swimmers, sometimes they wear it on their back or some part of their arm.
• The sensors are oftentimes attached with tape or sometimes just tucked under compression shorts. It just needs to be held in contact with the skin. It’s small enough that most people just forget that they have it on. It’s about the size of the bigger Garmin watches.

09:45 -

• You get a rich set of information about the athlete’s physiology out of that.
• We break this into several categories. We do assessments similar to what you do with the lactate threshold or the VO2max test.
• The goal of the assessment is to identify what aspect of their physiology is limiting their performance.
• However, where the Moxy is really different from other technologies is that you can use the same device in the field. You can use it to guide your daily training – interval training, long slow distance training, and recovery.
• You can even use it in competition. We have people that are using it to help optimize their race pace.

12:54 -

• The idea is that if you’re a cyclist and you transition from a power that’s below your FTP to a power that’s above your FTP, something reached its limit. There’s a reason why you can’t maintain that power above your FTP like you can when it’s just a few watts lower.
• When we talk about the limiter, we’re figuring out which system in the body is causing that to happen. The three that we typically look for with the Moxy are the respiratory system, the cardiac system, and the muscular system.
• We’re not saying that if it’s a limiter that it’s good or bad. Somebody who is a couch potato has a limiter and somebody that’s an Olympic level athlete also has a limiter.
• We’re not saying it’s the level of performance but we’re saying that when you go as fast as you can go, which system hits its limit first?

14:04 -

• It’s across the board. It amazes me how different athletes really are when we look at these plots.
• Some people who go as hard as they can go in one of these assessments, won’t desaturate. They’ll be up at 75-80% saturation and no matter how hard they go, they can’t get it to drop below that. This is an extreme case of muscle limitation. Their muscles can’t use all of the oxygen that the rest of their body is capable of delivering.
• On the flipside, you’ll see somebody who is desaturated down to 10-20% when they’re right at their FTP or even a little bit below it. This is an indication that they have really good muscle oxidative capacity in their muscles but their body can’t deliver as much oxygen as what their muscles can use.

15:16 -

• The Moxy measures two parameters. It measures the saturation (SmO2) and the total haemoglobin (THb).
• When it’s an oxygen delivery issue, that means either the cardiac system or the respiratory system can’t get enough oxygen to the muscles. In both of those cases, we tend to see low SmO2 (muscle oxygen saturation).
• The THb (total haemoglobin) is an indication of the blood volume in the muscle. That’s how we use it to interpret the data.
• When we’re seeing low saturation (SmO2), we look to the THb data. And if we see indications of vasodilation where the blood vessels are opening up and the blood volume is expanding in the muscle, this is an indication that the body has sufficient blood flow but you have vasodilators building up. This is because you’re not getting rid of CO2 fast enough.
• On the flipside, if we see vasoconstriction where the blood volume is going down, that’s the body taking action to restrict blood flow so that it preserves blood pressure for the brain.
• The body is really protective of blood flow to the heart and brain. It will shut down everything else in order to keep blood going to the heart and brain.

17:11 -

• ​The simplest way to think about saturation is the measure of the balance between supply and demand.
• If your body can deliver more oxygen to the muscles than what the muscles can use, which means supply exceeds demand, then the SmO2 goes up.
• Vice versa, if the muscles are wanting to use more oxygen than the body can deliver, then the SmO2 goes down.
• Essentially, the amount of oxygen that you’re using in the muscle is how much is extracted times the blood flow rate.
• It’s actually more efficient in some aspects to have low oxygenation in the muscle because then for every heartbeat you’re taking a lot of oxygen off of the blood and using it to do work.
• We typically like to see that low oxygen in the muscle because that means your muscles are able to use it and it’s an efficient use of your blood flow.

18:37 -

• This varies from athlete to athlete. There is a point where you learn how you respond when you get to that unsustainable point.
• The common response is that you get to a point where the SmO2 is going down a little bit and then suddenly it goes down a lot as you increase the load.
• This is one of the indications where you’re at a point where you can’t sustain the load anymore.

19:24 -

• The way that it is better is mainly that the information is much richer. You get more useful, actionable information when using the Moxy than what you would get from a lactate threshold test.
• People measure lactate because they’re trying to figure out what’s going on with the oxygen in the muscle. In the past, before devices like Moxy existed, it wasn’t possible to measure that directly.
• People measured lactate as an indirect indication of what’s going on in the muscle. It’s like reading about the sporting event the day after it happened rather than watching it live.
• With the Moxy, you can see live what’s going on in the muscle and not have to wait for the lactate response which is much more difficult to interpret.
• There are really two delays in this lactate testing. One is that there’s the physiological delay of how long does it take the body to reach homeostasis at a new load, which is typically 3-5 minutes.
• The next delay is that the lactate has to circulate through the body so that you can measure in the finger and try to infer what happened back in the muscle.
• With the assessments that we do for Moxy, we recommend a 5-minute step length which is longer than what a lot of the other assessments recommend. This is to really help us get to that homeostasis point.
• What’s nice is that you’re not drawing blood and you’re able to get data continuously through the entire test. You’re not just getting it at discrete points. It’s more practical to have those longer load steps when we’re doing those kinds of assessments.

22:42 -

• There’s actually some complementary information and a lot of our more serious training centres use both VO2-testing and the Moxy.
• ​You can get more detailed information about what’s going on in the respiratory system when you also measure it with VO2.
• The limitation there is it’s just not practical to wear a mask during regular training, even with the portable VO2-machines.
• A lot of the information that you get out of the VO2 can be inferred out of the Moxy but of course, it’s better to get it direct from the metabolic cart if you can.

23:55 -

• We try and measure the zones directly rather than calculating them from a fixed point. A lot of the time, someone will calculate an FTP and then they’ll say your zones are some percentage of your FTP.
• We typically break it into three zones. The low-intensity zone which we call the oxygenating zone. This is where the harder you go, the higher your oxygenation gets.
• This is where supply exceeds demand. It’s like you’re still warming up. If you’re at a low enough intensity, you won’t fully warm up. You won’t get to a point where your blood vessels are fully dilated and you won’t fully maximise your SmO2. You might only get up to 80% and you won’t go any higher. If that’s the case, then you’re still in that oxygenating zone
• At some point, you get to an intensity where your body will fully warm up and you’ll reach your peak. Typically that is 85-95% SmO2. This is a typical high point for most people. This will sustain over a range of loads.
• You can increase the load and your oxygenation doesn’t change much. We call this homeostasis because your body can just deal with it. There’s a range of loads at which you’re in homeostasis. 
• Then you get to a point where if you go harder, your body has to extract more oxygen to keep supplying the load. This doesn’t mean that you’re over your FTP necessarily. It does mean that your body is changing how it adapts to that increasing load. We call this the deoxygenating zone.

26:31 -

• We tend to use them directly because there’s a lot of baggage with the terminology of the thresholds.
• One example is if you’re going to do a recovery ride or run, we would typically do that at the very low end of the homeostasis zone – the transition between oxygenating and homeostasis.
• This gets you in a situation where you are minimising the stress. You’re doing the lowest intensity that you can but still get the oxygenation as high as you can.
• This is perfect for recovery. You’re getting a really good blood flow and lots of oxygen to the muscles but you’re not inducing any more stress than is necessary.
• If you’re going to do a threshold pace or power where you want to be right at the edge of as fast as you can go, then you’d be at the other end of that homeostasis.
• This is where if you go any harder, your oxygenation goes down. If you back off a little bit, your oxygenation will pop back up.
• If you’re right on that edge, we can use that to guide that intensity as well.
• What’s really nice about both of those is it may not be a fixed power. If you’re not well recovered or if it is a hot day, you might have that transition at a lower power than what you would if you were fully recovered.

29:04 -

• A lot of the time people talk about these as anaerobic zones but they don’t have to be and you can manage them really well using Moxy to guide it.
• If you’re going to do high-intensity intervals – let’s say you’re going nearly all out – and you want to be able to do a lot of them over and over again.
• If you watch your SmO2 as you start out doing the high-intensity interval, your SmO2 is going to drop fast because you’re way over your FTP.
• As soon as your SmO2 reaches its low plateau, which might be 20% for some people or 50% for others, as soon as you get there, stop and then recover until your SmO2 gets back up to its recovery point which is 80-90%. Then once you’re recovered, you can go again.
• If you use this method, you’re actually staying aerobic because the whole time you’re doing the high-intensity interval your oxygen is going down.
• This means that you’re using all of the oxygen that your body can deliver plus the oxygen that’s stored in the muscle which is the myoglobin aspect of what we measure.
• By doing this, you can avoid getting into the situation where you go anaerobic. You stop right before you have to use your oxygen-independent sources of metabolism.
• We’ve seen where people can do many more intervals than they could otherwise because they’re not burning the matches. They’re not using up they’re oxygen-independent stores of metabolism. They’re able to stay aerobic while doing this.
• This is a way to guide your interval training to maximise your oxygen utilisation capacity of your muscles.
• Another aspect is that if your goal is to stress your cardiac system, you would want to set your interval intensity so that you could maintain it for 5 minutes. Tweak your intensity so that you would go from peak SmO2 to your low plateau over a period of 5 minutes rather than dropping in 30-45 seconds.
• This gives your cardiac system enough time to get fully up to speed and you’re going over your FTP so you’re working your cardiac system as hard as you possibly can. Then you stop and let that recover.
• So again, you’re staying aerobic because you’re not continuing to do work after you’ve reached that low plateau but you’re giving your cardiac system enough time to make it work as hard as it possibly can.
• This is a way that you can target a particular system. Whereas, if you’re doing all-out intensity, your heart rate never gets up to the full intensity. By the time you’re done with the interval, your heart rate isn’t even maxed out yet.
• This is another way where you can dial the training in to accomplish what you want to rather than just leaving it to chance.

33:10 -

• It depends a lot on the individual. The interval training is great for helping people to improve their muscle oxidative capacity. The people who really need to do interval training are the ones who can’t desaturate well.
• We have people who did the interval training for a few months and they go from not being able to desaturate at all to be able to start to desaturate.
• As mentioned earlier, a lot of people start finding that they can do many more intervals than previously when they control this training with Moxy.

34:56 -

• Moxy is worthwhile for athletes who want to get faster efficiently or improve their performance more efficiently.
• Also, if you want to learn more about yourself and your physiology, if you want to be more involved in your training and understand how your body is reacting and learning to adapt when you’re fatigued, Moxy is important.
• To some extent, if someone is brand new to sport, one who is going from being a couch potato to just starting to exercise, it’s probably not as useful.
• As far as where to go, if you go to our website, we have a Training Centres tab there. We have certified training centres all around the world. A lot of them do remote training.
• For athletes who want to get hooked up with a training centre, contact us and we can get you referred to a training centre that would be a good fit for you.
• We also have some self-trained athletes. We have some training materials that are available on the website.

37:04 -

• One of our training centres in Canada has 11 Ironman triathletes, 9 of them had personal records after they started using Moxy.
• Another interesting one is Nike. They have been working on a project to try and achieve the first sub 2-hour marathon. They just had a documentary posted on that recently. If you look closely, you can see that they’re using Moxy.

40:16 -

Favourite book, blog, or resource related to endurance sports:
DC Rainmaker

• DC Rainmaker

A personal habit that helped achieve success:

• ​Focus and tenacity

What you wish you had known or done differently at some point in your career:

• ​I wish I had done more work with programming.

• On the Moxy Monitor Website
• On the Moxy Youtube channel
• On Twitter - @MoxyMonitor

• Moxy Monitor
• Threshold Confusion: Aerobic, Anaerobic, Lactate, Functional - Help! | EP#71 - On That Triathlon Show
• To lab test or not to lab test with Alan Couzens | EP#79 - On That Triathlon Show
• Hands-on with the Moxy Muscle Oxygen Sensor - by DC Rainmaker

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