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Using SmO2 for Threshold Intervals

SmO2 Provides Real-Time Physiological Info

Textbook SmO2 desaturation and Vo2 tipping point
Moxy SmO2 values give you an instant, physiological value for what is, and what isn’t, sustainable. It’s a noninvasive way to get accurate, autonomic data about aerobic and anaerobic tipping points.

Here is yet another example of the utility of an Smo2 sensor. This workout was performed by a client as well as myself last week. The goal of the intervals was to improve fitness at Lactate Threshold.

I may be a bit old-school, but I’ve essentially distilled cycling workouts to three simple levels of intensity; Breathing, Heaving, and Gasping.

  • Breathing workouts are easier, they’re aerobic, and they’re meant to improve Economy and Stamina. They burn mostly fat, but they’re on the easier side.
  • Heaving Workouts are harder, but they’re sustainable for up to 60 minutes. These would be ‘Speed’ or ‘Threshold’ type workouts.
  • Gasping workouts are super-hard, with high heart rates and respiratory rates, and they can’t be sustained for more than 6 or 8 minutes.

SmO2 works better than heart rate in all three of these types of efforts.

SmO2 – Saturated Muscle Oxygen

Moxy’s SmO2 sensors measure the amount of oxygen in your muscle. I tend to use it on my left quad, and sometimes on my left deltoid. When either my clients or myself uses it on the left quad, we get a great range of saturation, from 2-80%. With proper placement and use over time, we can get a really solid and consistent value for finding the highest sustainable power output, aka, “THRESHOLD”. When SmO2 drops BELOW that value, well, you’re on “Borrowed Time”.

Get SmO2 too low, and you're on Borrowed Time
Get SmO2 too low, and you’re on Borrowed Time.

Here are several GREAT examples!

THRESHOLD INTERVALS ARE ABOUT SUSTAINABILITY

Everyone knows about Heart Rate Zones. We’ve been using them, plus Wattage Zones now, for Decades. But the Heart tends to drift. Our bodies tend to act like bad oil filters; we work harder internally for the same external output over time. However, when we employ SmO2 sensors, and we know right where we are in terms of what the balance of Oxygen Supply and Demand is, well, we can get more work done. We can sustain this intensity more acutely. When we finally ‘Tip Over’ the Threshold, well, SmO2 shows that we’re on ‘Borrowed Time’.

Let’s Zoom In on these Intervals. We’ll start with an 8-Minute effort. This set of intervals was a ‘Reverse-Fibonacci’, and it was a set of 8-minute, 5-Minute, then 3-minute, 2-minute, and finally 1-minute intervals, with equal recoveries. It’s modeled after a Ronneveld Study, but I’ve been using regular Fibonacci efforts (1,1,2,3,5,8 sequence) for decades on the advice of Dr. Conrad Earnest, my mentor.

SmO2 captures Tipping Point Between Threshold and Vo2.
I included the ThB (Total Hemoglobin) on this image because it shows how the heart and lungs continued to work, harder and harder, to get oxygen to the muscles, even while the muscles were becoming less and less efficient. Craig’s ‘Tipping Point’ or ‘Threshold’ for Oxygen Supply and Demand is right at 17%. For the first half of the effort, he was riding with sustainable power. However, once he got to 17%, it dropped sharply, and he ‘Tipped’ into Vo2max territory, which is ‘BORROWED TIME’.

 

Next, let’s look at the 5-minute Interval.

5 Minute Interval at Threshold Using Moxy SMO2
Here it is again – wattage is fairly uniform, but ThB continues to rise, showing the strain, and right about the middle of the interval, just above the 17% Value, Smo2 starts to drop in to ‘Borrowed Time’.

 

Here’s the SmO2 Value for the 3-minute Effort.

3-Minute SmO2 and Thb Value Tipping Point.
For the 3-minute effort, You can see how SmO2 dives down to 16-17% early, then he literally holds it right there for the duration of the time period, until the LAST 30 SECONDS. The difference in wattage begins at the first red arrow. He shifted and pumped out more watts to finish. This led to a lowered SmO2 and near-exhaustion.
***also note: ThB for the middle part of the effort plateau’d. We don’t use THB as much as we should, but it’s another great indicator that a physiological intensity is sustainable – or not.

 

At 2 Minutes, and over 600 KiloJoules of Work Performed Thus Far, It’s Hard To Get Below Threshold

 

2 Minute Interval at Threshold Using Moxy SMO2
If this workout had been 3,2, and 1-minute intervals, we would have worked hard to get SmO2 Below that 17% value early, and to try and hold it there as long as possible. But after numerous high-quality efforts, SmO2 won’t dip, and this becomes, once again, a THRESHOLD EFFORT. Which was the goal.
The RISE in SmO2 at the vertical line occurs because he Stood, off the saddle. This changes muscle dynamics and force. He dropped from 100 to 60 rpm, and while power went up, he once again, WAS ON ‘BORROWED TIME’!

 

The Grand Finale; a 60-Second Effort!

1 Minute Interval at Threshold Using Moxy SMO2
For a 1-minute effort, we’re almost completely past the tipping point. I placed the vertical marker at 16% and you’ll see that the value stays BELOW that number EVEN AFTER THE EFFORT ENDS. The entire effort was performed well north of 300 watts, and this yielded a LARGE metabolic penalty. ThB continued to rise and while we can’t add another metric to the chart, Heart Rate was well above 95% of HRR.

Moxy and SmO2 are POWERFUL Tools

You all know – I have promoted wattage and power and kilojoules since FOREVER. But going forward, I’m going to be more nuanced. The body is a machine, but it’s a machine with huge variations in recovery, genetic ability, and psychological, almost psychotic abilities to suffer. Using a Moxy and SmO2 to determine the ‘Goldilocks’ intensity for Threshold Intervals gives us an ideal intensity FOR THAT DAY, FOR THAT MOMENT, FOR THAT DURATION. If you’re a Moxy owner, try to find your ‘Tipping Point‘ of desaturation, and then back off JUST ENOUGH to give it a sustainable, but powerful effort. Try it on a hill. After all – we don’t live on a Space Station.

I just did that this weekend, when I rode a couple of hills on a route that was unfamiliar. I used another feature on the Garmin, the ‘ClimbPro’ option (I’ll have to talk about that in another post), but here’s how it worked.

Richard Wharton Using Moxy when Climbing a Hill
This was a 6-minute hill, give or take, on an unfamiliar route. Average gradient was about 7%. I followed the ClimbPro until I knew that I was maybe 700 Meters from the end of the effort. Looking at the SmO2 data, I kept the Saturated Oxygen above 25%, and when I knew where the finish was, I increased the power EVER SO SLIGHTLY until it dipped down to about 20%. In this graph, you can also see the deflection point of ThB, and then the continued rise once I pushed it past the Tipping Point.
I was on Borrowed Time, but I knew where time could stop.

 

Get a Moxy and Use SmO2 For Accurate Training and Sustained Efforts At Power.

I know this is HIGH NERD STUFF. But it’s fascinating, and it’s useful. If you own a Moxy Monitor, use the Steve Neal Field and the lap function, and watch for your ‘Tipping Point’, indoors or out. You don’t want to be on ‘Borrowed Time’ for those longer intervals or hills!!!

Thanks for reading, and ENJOY THE RIDE!

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Like what you see in these posts? Why not take the next step? Coach Wharton is currently accepting new clients for both Xert and PerfPro training methodologies. He is also available to discuss specific questions or equipment/training issues—just  schedule an online video consultation.