Fat Burning – Running vs Cycling

In a previous post I took at look at the exercise intensity which produced the maximum fat oxidation rates (Maximal Fat Oxidation Rates in an Athletic Population). A study took a look at the fat oxidation rates which happen when exercise is performed at the FATmax rate with cycling and running.

There was a significant difference in the rate of fat oxidation between the two (Juul Achten, Michelle C Venables, Asker E Jeukendrup. Fat oxidation rates are higher during running compared with cycling over a wide range of intensities. Metabolism, Volume 52, Issue 6, June 2003, Pages 747-752.).

Maximal fat oxidation was 28% higher when walking [ed: did they mean running?] compared with cycling, but the intensity, which elicits maximal fat oxidation, is not different between these 2 exercise modes.

These are interesting results. Although both exercises were done at the same intensity level (as measured by heart rate) they resulted in different amounts of total fat oxidation.

This leads me to conclude that although cycling and running can be both done at the MAF heart rate they are not equal for fat oxidation rates.

What About Rowing?

It would be interesting to see what the fat oxidation rate at FATmax is for rowing (ROW) and other modes. Turns out there’s a study for that too. (Egan B, Ashley DT, Kennedy E, O’Connor PL, O’Gorman DJ. Higher rate of fat oxidation during rowing compared with cycling ergometer exercise across a range of exercise intensities. Scand J Med Sci Sports. 2016 Jun;26(6):630-7. The study found that:

…FATox is higher during ROW compared with CYC exercise across a range of exercise intensities matched for energy expenditure…

The details show:

Despite similar oxygen consumption, rates of fat oxidation (FATox ) were ∼45% higher during ROW compared with CYC (P < 0.05) across a range of power output increments.

The crossover point for substrate utilization occurred at a higher relative exercise intensity for ROW than CYC (57.8 ± 2.1 vs 42.1 ± 3.6%VO2peak , P < 0.05).

Putting the Pieces Together

  • Rowing is ~45% better than cycling.
  • Running is ~28% better than cycling.
  • Rowing should be ~17% better than running.

Mechanism to Explain Differences

The degree to which an exercise engages muscles determines the maximum fat oxidation. Rowing has more muscle involvement than running which has more muscle involvement than cycling.




MAF Bike Ride

A couple of days ago I did a MAF bike ride. The ride was 1 hr 40 minutes.The route was up the Great Allegheny Passage Bike Trail.

Here was my heart rate data.

I was able to keep very close to my MAF heart rate for the majority of the ride time. There was a big hill in the way home that made it hard to hold the MAF rate near the end.


A Long Bike Ride

I took a look at a 3-hour long bike ride (Exercise Intensity on Low Carb) last month. I did the ride at a average heart rate of 138 bpm.

I took a longer ride later that same week and I have the data from that ride. How does the data from the ride compare to my recent thoughts on Heart Rate Training (HRT)? I did push myself as hard as I could on the ride. What I am interested in is the question in reverse. That is, if I push hard and long what was my heart rate?

From the HRT data and my own VO2max testing I know that my aerobic (fat fueled) zone is at a heart rate of 112-122 bpm. That means that at a higher heart rate (level of exertion) I am burning down my glycogen stores. (That is a problem if you are Low Carb.) After this long ride my blood sugar was pretty low (in the 50’s). Clearly from my blood sugar, I burned through my glycogen stores.

Trail Route

Here’s the trip I took along the Great Allegheny Passage Trail. I took the trip with my 14-year old son. I think I almost killed him. The GPS and heart rate data dropped out a couple of times along the way but here’s the map.

It was a long ride at almost 4 hours of riding. My speed at 8.8 mph was really slow. Here’s the details of the ride.

The data showed my average heart rate at 125 bpm. Hard to tell exactly where it was but here’s the graph that the program recorded. This was clearly an endurance event. The green line is approximately my MAF heart rate of 112-122 bpm. It is pretty close to the average of 125 bpm on the ride. The fact that there was activity above the line indicates that some portion of that activity was fueled by carbohydrates (glycogen stores).

Fat Oxidation Rates

That’s a total of 227 minutes and 1398 calories. This is a fat oxidation rate of 0.68 g/min (assuming all of the activity was fat fueled – which is wasn’t). That is very close to the rate noted here (Nutrition. 2004 Jul-Aug;20(7-8):716-727. Optimizing fat oxidation through exercise and diet. Achten J, Jeukendrup AE.).

With increasing exercise intensities, the fat oxidation rate increased to a maximum of 0.60 ± 0.07 g/min at 64 ± 4% VO2max (range 42-84), which corresponds to 74 ± 3% HRmax (range 54-92).

Future Plans

I want to repeat a long endurance ride with my heart rate limited at 112-122 bpm and see how my performance turns out.


Exercise Intensity on Low Carb

The Low Carb diet requires use of fat as the primary fuel source. Fat as fuel is only available at a particular maximum rate. The rate fat is used as fuel is the fat oxidation rate.

The other ordinary source of energy is from carbohydrates. Carbohydrate stored in the human body are in the form of glycogen and are much more limited than fat as a fuel. On the Low Carbohydrate diet, Glycogen stores are reduced from other diets so there’s less substrate available for fuel. In the body, glycogen is stored in the liver and muscles.  Glycogen in the liver is used for Gluconeogenesis which produces glucose for the parts of the body which require glucose. Glucose in the muscles is used for energy.

This paper is a good source of material on this subject (Sports Med. 2014; 44(Suppl 1): 87–96. New Insights into the Interaction of Carbohydrate and Fat Metabolism During Exercise. Lawrence L. Spriet).

Fuel Source Depends on Diet

We are always a hybrid mix of carb and fat fueled. Someone on a High Carb (HC) diet is primarily carb fueled. On a Low Carb (LC) diet that person is primarily fat fueled.

With Low Carb, at t=0:

Carb oxidation rate is about 0.4g/min (1.6 kCal/min) and fat oxidation rate is 1.2g/min (10.8 kCal/min). That’s a combined 12.4 kCal/min or 744 calories per hour.

With High Carb, at t=0:

Carb oxidation rate is about 1.75g/min (7 kCal/min) and fat oxidation rate is 0.55g/min (4.95 kCal/min). That’s a combined 11.95 kCal/min or 744 calories per hour.

The fat oxidation efficiency is noted in other studies at about 10% lower. These rates are in trained athletes. These are also at longer endurance paces where the fat fueled athlete is on equal or better footing.

Fat Oxidation Rates

There is a study of the maximum amount of fat that can be oxidized at various levels of exertion (Nutrition. 2004 Jul-Aug;20(7-8):716-727. Optimizing fat oxidation through exercise and diet. Achten J, Jeukendrup AE.).

With increasing exercise intensities, the fat oxidation rate increased to a maximum of 0.60 ± 0.07 g/min at 64 ± 4% VO2max (range 42-84), which corresponds to 74 ± 3% HRmax (range 54-92).

The intensities of the Fatmax zone were located -8.9 ± 1.3% and +8.2 ± 1.2% from Fatmax. The Fatmax zone was found to be between 55 ± 3 and 72 ± 4%VO2max, which is equivalent to 68 ± 3 and 79 ± 3%HRmax, respectively.

At exercise intensities above the high border of the Fatmax zone, fat oxidation rates decreased markedly. The contribution of fat oxidation to energy expenditure became negligible above 89 ± 3%V02max (range 71-99) and 92 +I %HRmax (range 84-98).

My Own VO2max Numbers

On my own case, my fat max oxidation was at a heart rate of between 90 and 120 BPM (nominal peak value of 100 BPM). My RER reached 0.85 (carb/fat fuel mixed evenly) at a heart rate of about 138 (85% of my max heart rate).

A rate of 0.6 g/min (36g/hr) is 5.4 kCalories per minute or 325 kCalories per hour (maximum rate). The highest fat oxidation rate recorded was Ben Greenfield who burned at 1.5g/min or 810 calories per hour.

My Three Hour Bike Ride

I took a three hour bike ride where my watch said I burned 900 kCalories. That’s 300 kCalories per hr which approaches matches the maximum fat oxidation rate.

My heart rate was around 138 which is 85% of my HRmax. That is close to my 50-50 crossover (half carbs and half fat burning) from my VO2max test.



Fat Adapted Athletes

Here’s a great study on fat adapted athletes (Lambert EV, Speechly DP, Dennis SC, Noakes TD. Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet. Eur J Appl Physiol Occup Physiol. 1994;69(4):287-93.).

The study looked at five cyclists and compared them on a High Carb vs a High Fat diet.

Despite a lower muscle glycogen content at the onset of MIE [32 (SEM 7) vs 73 (SEM 6) mmol · kg −1 wet mass, HIGH-FAT vs HIGH-CHO, P < 0.01], exercise time to exhaustion during subsequent MIE was significantly longer after the HIGH-FAT diet [79.7 (SEM 7.6) vs 42.5 (SEM 6.8) min, HIGH-FAT vs HIGH-CHO, P<0.01]

Looks like they have an almost 2x advantage when it comes to endurance.

How long did it take to convert these athletes from Carb Adapted to Fat Adapted?

These results would suggest that 2 weeks of adaptation to a high-fat diet would result in an enhanced resistance to fatigue and a significant sparing of endogenous carbohydrate during low to moderate intensity exercise in a relatively glycogen-depleted state and unimpaired performance during high intensity exercise.

Only two weeks!


Bicycle Trainer – Repost from Dec 2016

A bike trainer is the stand that your rear tire gets mounted to. It has a friction mount to the tire surface. I decided I wanted to change the bike from a mountain bike into a comfort bike so I went back to Bikes Unlimited and bought a comfortable padded seat plus cruiser handlebars. Here is the result.

Got a real workout just setting it up. Linking the videos I used to get past the rough parts below.

When I bought the trainer, I purchased a new smooth tire to replace the knobby tire that was on the bike. Getting the old tire off was tough but getting the new one on was even tougher.

I bought a new inner tube to match the tire size and once I got the new tire mounted I had a problem with my pump and the tire valve. My pump, like all cheapo pumps has a Schrader valves and my new tubes were Presta valves. Went to Bikes Unlimited and they had an adapter for $2.

Bought new handlebars there ($20) and a new seat ($40+). Took a break then did a short six minute ride. I forgot how the shifter works (there is a second button behind the bars. Had to adjust the breaks.

I like it! Now I just need to ride it.

P.S. 2018-06-29: December was a lousy time to take up riding a bike outside in Western PA. I rode it a few times indoors over the winter but not much. My last ride indoors was 1 hour just to see what my endurance is on the bike. It was pretty boring.

To improve I will probably set it up again this winter and ride for heart rate training during the cold months.

The regret is that I didn’t spend more and get something that I could monitor power output with. Then I could do metrics to see if I improved my power output.


Does Exercise Increase Energy Expenditure While Dieting?

Here is a study that looked at resting energy expenditure (REE) under a calorie restricted diet (L C Henson D C Poole C P Donahoe D Heber. Effects of exercise training on resting energy expenditure during caloric restriction. The American Journal of Clinical Nutrition, Volume 46, Issue 6, 1 December 1987, Pages 893–899).

The seven subjects were moderately obese women put on a calorie restricted diet. The test was lasted nine weeks. They were exercised for three weeks at the end of their diet at 70% of their VO2max.

Resting energy expenditure (REE), maximum oxygen uptake (VO2max), and body composition were measured in seven moderately obese women during 9 wk of dietary restriction (800 kcal/d). During weeks 4-6, subjects underwent exercise training (30 min cycling/d, 5 d/wk, at 70% VO2max).

The conclusions were:

The first 3 wk of caloric restriction decreased REE by 13% (from 1437 +/- 76 to 1254 +/- 66 kcal/24 h, means +/- SEM, p less than 0.05).

That shouldn’t be a surprise since weight loss results in a reduction of Energy Expenditure.  The numbers need to be compared closely to the actual weight loss to see how much of the reduction in TDEE was from the weight difference and how much was from metabolic adaptation.

How was their performance affected?

Exercise training increased VO2max (from 1717 +/- 108 to 1960 +/- 120 mL/min, means +/- SEM, p less than 0.05)

Their VO2max showed a substantial improvement for only three weeks of training. It would have been interesting to have a control group which was not put on the exercise program to tease out whether some of this was due to weight reduction or it was due to the exercise.

but did not elevate the dietary-depressed REE (from 1254 +/- 66 to 1262 +/- 62 kcal/24 h).

It looks like the REE did show an increase but it was not statistically significant.

The greatest decrease in body fat (3.7 +/- 0.4 kg) occurred during exercise training, resulting in a small apparent increase in REE when expressed per kilogram total body weight. However, expressed per unit lean body mass, REE remained suppressed throughout the period of caloric restriction.

At 70% of VO2max they were at a good rate for loss of both carbohydrates and fat stores. It would be interesting to see their actual rates of substrate metabolism.

Their conclusions?

We conclude that exercise training of sufficient intensity to substantially increase VO2max does not reverse the dietary-induced depression of REE.

This is interesting since there’s a common assumption that exercising will cause people to burn more calories at rest but that wasn’t the case in this particular situation.

However, the increase in VO2max itself was worthwhile as it indicates a gain in fitness.