MAF Walk with New Polar Heart Rate Monitor

I bought a rower and Polar H7 heart rate (HR) monitor. I took the H7 out on my MAF walk/run this morning. I collected data on my watch and on the heart rate monitor. Both had dropouts at points but they correlated well. I want to get to where my RPE is accurate enough that I don’t need to keep checking the watch but I do have a tendency to push it up past my MAF HR range.

Here’s the heart rate data from the H7 HR monitor. The H7 reported an average HR of 107 bpm. I think I did not have the strap high enough in the first part of the walk.

Here’s the heart rate data from the Samsung Gear Sport Watch monitor (Strava data). The watch reported an average HR of 111 bpm.

Here’s the same graph out of Samsung Health app on the phone.

The 113 bpm grid line would be the bottom of the 112-122 bpm MAF range so the HR between 20-40 minutes should be on or above that line.

Looks like my warmup was too quick and my cool down still could be better but overall it feels pretty good.


I walked to the Post Office and then up the hills. Both of the GPS data were good.


It was a lot cooler at 57 degrees this AM so my performance was better. I accidentally paused the watch a couple of times so the Strava length was more accurate and I assume the splits were more accurate as well. I am getting to where I have to run in stretches to keep up the MAF HR and the stretches keep getting longer as well.

Here’s the performance data from the watch:

Ultra-Endurance Walking and Running Events

A study looked at the studies on fueling ultra-endurance events. Ultra-endurance is defined as activities (walking and running) which take at least 6 hours. The study was (Eric Williams. Nutritional implications for ultra-endurance walking and running events. Extreme Physiol Med. 2016; 5: 13).

Given that the majority of an ultra-endurance athlete’s training is spent engaged in lengthy durations of aerobic activity, many of these athletes are well adapted to utilizing lipids via oxidative phosphorylation

Fat burners! But during the event itself how hard are they hitting it?

When the athlete is exercising at the standard marathon pace that requires 80–90% of maximal oxygen consumption (VO2 max) or above, carbohydrate will be his or her primary fuel source and could provide up to 96% of the energy being expended.

This is an issue with Low Carbohydrate diets since glycogen stores are reduced greatly. This is also why Phinney’s endurance tests are done at 62% of VO2max.

The paper had a nice graphic which shows the elements involved in performance in marathons.

Each of these would be interesting to look at in detail.


MAF Test – Triathlete Friend

My friend, SVW, did a MAF test the other day (2018-06-27). He is 35 year old triathlete who runs regularly. His MAF Heart Rate is 135-145. Here’s his Heart Rate chart.

He did a fine job of keeping his HR between 144 and 145. He did not do a 20 minute warm-up but ran to get his heart rate into the range. His mile splits were:

He did well at holding heart rate and his pace was pretty even throughout. That’s what I would expect out of a trained runner (he has been running for 5 years).

SVW is fat adapted and did keto for a year or so. He still eats keto mostly (some off and on). He does believe he needs carbs to compete in marathons.

Compared to Me?

SVW is almost twice as fast as me at my MAF heart rate. Some of this is age. Some of this is conditioning. I was walking and he was running. Some of this is motivation. Here’s my MAF test splits.

I don’t believe that SVW is interested in MAF training. He’s convinced that where he is at he needs to build his anaerobic base.



Took today for a recovery day after my 5K walk with additional 5K warmup yesterday. Feel pretty good. Not sore or tired at all today but I want to respect the protocol and the 93 degree heat outside today to take a rest day.

Walked a total of 10K yesterday. Pretty sure that was the most walking I have ever done in my life. I credit Crossfit for getting me into the physical shape I am in now.

I am hopeful that the Maffetone method of Heart Rate Training will take me to the next level.

My watch indicates I trained for 5 hrs ,33 minutes in the last week.


MAF 5K Walk with 5K Warmup

I did Chef Joe’s Omelette Run today at my MAF  heart rate (112-122 bpm) this morning. I got to the race early to make sure I got a shirt and walked a 5K as a warmup before the 5K race. I did the race and warmup walking only (no running).

5K Warm-up for 5K Race

I did a 5K walk as my warm-up on the track.

Here were my splits in the warm-up.

Here are the statistics for the warm-up.

I did pretty good at keeping in my MAF heart rate range of 112-122.

It took about 20 minutes to get up to my MAF range. The warm-up ended about 25 minutes before the race but I kept moving after the warm-up.

The 5K Race

Here’s my heart rate during the race. I stayed in the MAF range for the most part. Because I was already warmed up I got into my MAF range in just a couple of minutes.

Here were my splits for the race (walk). My race splits were better than the best warm-up splits.

Here was the route. Not too much hills considering it is here in SW PA. I did find it challenging doing the walk with other people since I tried to keep up with the women in front of me but that made my heart rate go up over the MAF number.  When that happened I breathed deeply and held in my breath at the in breath. That seems to drop my heart rate a few points quickly.

As you can see I hit 137 bpm at one point. I did throttle back pretty quickly. It was getting hot even at 9 AM but the temperature above is recorded as 69.5 F.

I had fun. And I represented keto…

Heart Rate Training (HRT) – Part 13

Part 1 of this series.

Last month I was not following the Maffetone method. I was getting up in the morning and running as fast as I could. I captured the data from one run around my neighborhood. This is the map of the 1.4 mile loop I ran around my neighborhood.

Elevation Data

That run has a pretty decent uphill (and downhill is even steeper) which makes the heart rate challenge even more difficult.

My Heart Rate Data

During my run, I also recorded my heart rate data. My average heart rate was 157 bpm and my max heart rate was 173 bpm. The average includes the warm-up section at the start. The average after warm-up was more – somewhere around 162 bpm. This is my max heart rate from the 220 minus age method. At 173 bpm I was over the 220 minus age method value. Probably not a great thing to do.

How does this correlate to my VO2max numbers? What was I burning when I was running? My chart from the last post was:

HR RER %Fat %Carbs
120 0.70 99% 1%
125 0.74 88% 12%
130 0.77 77% 23%
135 0.80 66% 34%
140 0.84 55% 45%
145 0.87 44% 56%
150 0.90 33% 67%
155 0.94 21% 79%
160 0.97 10% 90%
165 1.00 0% 100%

This shows nearly all of my run was fueled from carbs and almost none of the run was fueled from fat.

What’s Wrong with Burning Carbs?

This level of heart rate is not sustainable for very long when on a Low Carb diet. Running burns about 100 calories a mile. That is a significant portion of the body’s store glycogen store. Additionally, the body is glucose sparing when on Low Carb so it resists the additional glucose that is in circulation.

My Pace

My pace wasn’t all that great either. The app shows the average pace of 9:38.

Since I was at my heart rate max without training my heart rate to be lower my performance gains would have been hard fought.

Why Heart Rate Train?

Heart rate training offers the opportunity to improve performance within the fat burning zone. The promise is that speed will increase at the same heart rate as cardiac health improves.


Heart Rate Training (HRT) – Part 12

Part 1 of this series.

Second MAF Test

I did a five mile walk on a track tonight. It was an attempt to get a better MAF baseline. Here is the Strava (with my Samsung phone).

Here is my heart rate from my Samsung Gear Sport watch.

I did a good job of keeping my heart rate in the 112-122 range. I would have liked it to be a bit higher and still in the range but I am pleased with the results. Here’s my splits graphically (from the phone).

The splits show a good drop starting at the third mile. This is as expected. Also, I didn’t do a legitimate warmup, I just started into walking so it took about a half mile for my heart rate to get to the range. Next time I do one of these I will do a warmup and then start recording data when at the correct heart rate.

Here’s the happy walker after the 1-1/2 hours were completed.

If the MAF method works for me and I put in the training effort I should see those split times decline. Also, I should be able to start slow running soon.


Heart Rate Training (HRT) – Part 10

Part 1 of this series.

Dr Noakes to the Rescue?

I think we are trying to fit big feet into small shoes by trying to make Low Carb fit into exercise modes which are by design not compatible with being fat fueled.

I have great respect for Dr Noakes, but in my opinion the following video illustrates how we are missing the point when it comes to athletic performance and Low Carbohydrate diets.

Dr Noakes (@20:00) makes a startling comment in the video (@20:04).

There must be an exercise duration for which fat adaptation is the preferred state for optimal performance and I don’t know if we have found it yet…

Dr Noakes is humble in this video and admits that his own studies which showed advantages may have been biased – that was helpful for those of us who bought the hype that we can perform any sport on LC and do it well.

However, this video completely misses the point in a weird sort of way. People do low carb and get great benefits but find it doesn’t mix well with their particular athletic modality. In fact, they may find it doesn’t mix well with any competitive athletic modality. And, all athletics is artificial in some sense so to conclude that it is a bad diet based on some artificial measurement is missing the mark. Low Carb has found a home with triathletes and ultra-marathon runners but those are fairly elite choices.

What Dr Noakes is missing is that the real issue isn’t one of duration. The issue is one of fuel source. Certainly intensity and duration are inversely related. Sprints are intense and short. Ultra-marathons are low intensity but very long in duration. Few people want to do an ultra marathon.

We low carb athletic proponents are fond of touting the advantages of fat adaptation. It is true that the low carb athlete is better at accessing fuel but only out of necessity since the body spares carbohydrate stores on the low carb diet. The body doesn’t want to spend carbs on exercise since those stores are limited. But if you push your intensity up high enough it will pull from carb stores and these are limited in both depth and speed that can be accessed on a low carb athlete. This necessarily reduces exercise intensity to levels that are not competitive.

This is why folks who do Crossfit or take up wrestling find that they need to supplement carbohydrates. They chose to alter their diet to fuel their exercise rather than picking an exercise mode which matches their diet. Personally, I view this as a fundamental mistake.

What is the Answer?

The right answer is to engage in athletic activities which utilize the fat as fuel and don’t rely on carbohydrates as fuel. When a person is completely fat fueled they have a very deep tank of storage for energy. The use of fat as fuel necessarily translates to a reduced intensity which is problematic on any medium duration sports.

What intensity level is this done at? Here’s where some data can illustrate the point. Ben Greenfield published his own VO2max testing and I’ve plotted his VO2max numbers vs his RER numbers. (Remember that RER is a measure of fuel mixture. An RER of 0.7 indicates that the person is 100% fat fueled and an RER of 1.0 indicates a person is 100% carbohydrate fueled. An RER of 0.85 would be 50-50 mix of fat/carbs.)

Ben’s data is pretty jumpy so the red line is a 3rd order polynomial which is fitted to the data (the R^2 was 0.85). It shows a dip (more fat burning) at around 35% of VO2max. The data also shows a fairly flat line across the entire range from 25% to 50%. The actual data showing the dip is:

This is a very specific point in time where Ben Greenfield’s data showed him burning 97% of his energy from fat – clearly the sweet spot for a person who is fat fueled since almost none of the energy he was using came from carbs. Ben never got an RER below 0.7 so this is the best he did during that time. Unfortunately, that point is a pretty low point level of intensity. Well, sorta. Ben’s VO2max is 61.1 and that point was at a VO2 rate of 27.2 so the point where Ben was being as fat fueled as he possibly could be was at 45% of his VO2max.

This correlates well with other published data:

This shows a peak fat oxidation rate at 65% of VO2max but the issue isn’t one of maximum fat oxidation since at 65% the fat is mixed with carbohydrate oxidation. That does produce the most efficient exercise but only in a non-fat fueled athlete. The attractiveness of the data is that it clearly shows a fairly wide curve. The whole graph is relatively flat from 50% to 75%. But what is different between these two points is the fuel source in the body.

Fine Tuning Fat Burning

The spot is the highest intensity which can be reached where 100% of energy comes from fat and 0% from carbohydrates. I don’t know if there’s a term for this but let’s call it the Maximum Glucose Sparing/Fat Burning the MGSFB point.

I happen to know my MGSFB from my VO2max data. Here, I’ve added a bulls eye at the MGSFB point. At this point my RER was 0.7 and rising.

[Note for people trying to lose fat: I have no interest  at all in fat burning at this point in time but the implications of the above should be obvious for those who are interested in fat burning. You can get the most bang for the buck in fat burning at a level which is much less than your max heart rate. If you are beating yourself up in the gym that may be good news.]

My MGSFB was at 65% of my VO2max and it was at a HR. This matches the point at the top of the curve shown of fat oxidation rates vs VO2max. In fact, that could well be the very definition of fat adapted – ie, the ability to most efficiently burn fat at the highest VO2max point.

This was at a HR of 117 bpm. This correlates well to the center of the Maffetone HR value of 112-122 bpm. In fact, it might suggest that I should drop my range to 107-117 max since that guarantees I stay in the fat burning range for the entire activity

So how do you figure this out for yourself?

Here’s the approach I essentially took to get to this number:

  • Get fat adapted by adopting a Very Low Carb diet (< 30g of carbohydrates)
  • Do this for the TBD (days/weeks/months) adaptation period
  • Get your VO2max tested
    • If your VO2max doesn’t show you with an RER of 0.7 for a large portion of the test time you are not yet fat adapted
  • Plot the curve or just look at the data and find the highest point where your RER is still 0.7 or less
    • The point at which it goes over 0.7 you are no longer burning fat exclusively
  • Find the corresponding heart rate
    • That is your max heart rate for exercising

A Cheaper/Easier/Faster/Close-Enough Way

Just use the MAF calculation. It’s close enough. I like it enough that I wrote an MAF calculator and put it on-line here.


Exercise Studies

This will be an accumulated list of exercise related studies.

Athletic performance on Low Carb

Exercise and Diabetes

Exercise Physiology (Mechanisms)

Exercise Supplementation


Splitting Low Carb Studies BLOG into Two Sites

The Low Carb Studies BLOG is being split into two sites. The original Low Carb Studies BLOG will concentrate on the Low Carb/Ketogenic diet. This site will focus on Athletics on the Ketogenic Diet.

It will take a while to move the content over but allow more focus on each subject individually.