The purpose of this study was two fold:
Why study this?
This specific style of study is actually quite important because it sheds light on the most optimal way to use cardio for weight reduction. There's currently a large divide in the community with regards to high intensity training and low intensity training so this sort of information gives us a more clear direction.
Further, if you're just looking to get in better shape, this research will provide information about which form is best. If perhaps, cycling was more efficient than running (just an example), you could decide to use that form of exercise more often for more effective and efficient results.
12, healthy and moderately trained men were recruited for this study. Subjects were chosen based on being part of a club/county endurance cycling group and all had moderate experience for at least 3 years.
"Twelve subjects performed a graded exercise test to exhaustion on a cycle ergometer and on a treadmill; the results of this test were used to measure fat oxidation over a wide range of intensities for each subject during 2 different modes of exercise. The data were then used to determine whether the maximal rate of fat oxidation and the intensity at which it occurs were different when walking or cycling. The order of the trials was assigned to the subjects in a randomized cross-over design, and the tests were performed 5 to 7 days apart"
Essentially, subjects were required to do what is known as a graded test. For example, on the cycle, the participants started with a cycling pace of 95 W, meaning their overage power output was 95 W. Afterwards, their pace was increased by 35 W, every 3 minutes until exhaustion.
For the running test, subjects walked on a treadmill at 7.5 km / hour, starting at a 1% gradient. From here, the gradient was increase by 2% until an RER of 1.0 was reached. From here, the subjects ran at 10 km / hour at a 10% grade. Speed was increased by 2 km every 3 minutes until exhaustion.
Time Out! What's RER?
RER is taken using a gas exchange mask. It's a scale that measures your breath and determines how much carbohydrate and fat you're using as fuel. It's essentially a way to say "hey, you're preferentially burning fat (or carbohydrate) as fuel. Essentially, once this number is below 1.0, fat oxidation rises. For example: a 1.0 would be almost pure carbohydrate usage whereas a .70 would be almost entirely fat usage.
The researchers had runners walk until 1.0 to avoid unnecessary energy expenditure just trying to get to a fat burning state. For example, if the subjects were above 1.0 before starting, they may not ever get to a point that fat is being preferentially burned, rendering the study useless.
During this time, the researchers evaluated things like the rate of fat oxidation.
Throughout the course of the exercise session, the researchers could see at which time point and intensity, fat oxidation was highest, meaning that highest amount of fat being burned. From here, they can compare the results to a similar test, using running instead of cycling.
Lastly, during the testing, values for V02 and fat oxidation / carbohydrate oxidation were accounted for.
The researchers did this to be able to provide a representation of intensity and fat oxidation on the individual level. For example, the researchers can compare the subjects V02 to the amount of fat they're are using as fuel. After observing this for multiple subjects, we can begin to draw conclusions as to which amount of intensity is optimal for oxidizing fat.
Essentially, we can look at relative V02 (volume of oxygen consumption, as a metric for how hard you're working) and then look at the amount of fat being burned. Eventually we can begin to say "ok, at this level of V02, we can expect fat oxidation to be at this level, etc. It just brings a bit more real world application to the study.
When observing the relative amount of fat burning for each protocol, it was revealed that when running, the starting point and overall amount and rate of fat oxidation was significantly greater than baseline and over that of cycling. Overall, there was a clear advantage to running, compared to cycling.
Again, we see that for running, the starting point of fat oxidation rates is significantly higher for runners, compared to cycling. Further, we can see that the shift towards carbo utilization occurs at a very similar intensity, meaning that the mechanisms are the same, yet running is just a better option for fat burning.
Cyclists May Be More Efficient At Cycling
One very important consideration is that these individuals were regular cyclists for at least 3 years. When trianing constantly and consistently for a given sport, a primary adaptation is greater efficiency of movement and utilization of fuel.
It's highly probably that since these individuals were trained cyclists, the amount of energy they use during activity, during that specific activity (cycling) could be significantly less. By using running, of which the cyclists are not familiar, it's possible that the increased energy expenditure is simply due to the fact that these individuals were not trained runners.
Essentially, it's very possible these findings are not because running is superior, per se, but rather because running is a novel stimulus, meaning the body burns more energy trying to keep up with energy demands. Essentially, we'd need to repeat the study, using seasoned runners in the same capacity as the cyclists used in this study to determine if the effect seen in this study is due to novelty of exercise or if running is in fact, superior.
Running Is More Intensive
Another factor to consider is that running as a whole is far more intensive in terms of what is required to move, meaning a greater amount of energy being needed and used.
For example, running requires coordinated movement of legs, torso and arms, where as cycling is primarily dependent on lower limbs. Surely cycling involves other muscle groups to some extent but it's safe to say that they level of activity required by running for many muscle groups is greater than what is required to stay on a stationary cycle.
Perhaps the increased energy demand of running is the explanation for these findings. It's certainly possible and doesn't necessarily nullify the results. If running requires more energy, then you'll use more energy to satisfy that need.
Small, Concise Population
Another important consideration is the sample size. Only 12 participants from a very specific group of individuals were chosen. Further, due to technical issues, only 6 of the 12 had blood drawings. This could potentially make the findings less strong, to say the least.
I personally would have liked to see a population of trained cyclists, trained runners and untrained, overweight individuals, to determine how training status affected the findings. If this could be done, we could draw some serious conclusions.
Overall, these findings aren't conclusive enough to say stop cycling at the hand of running. Surely it opens the door to possibility, but due to the factors I discussed, it's difficult to definitively say running is better. Certainly, running is much more difficult, at least for me, leading me to believe that energy expenditure will probably be greater.
Additionally, it's hard to know if the benefit of running over cycling was simply because it was a novel stimulus to those whom regularly cycle. Further, it's hard to know if these trained cyclers were simply more efficient at cycling (very possible).
I'd suggest using a combination of running and cycling if you're looking to drop some pounds, using cardio based exercises, potentially placing greater emphasis on running over cycling. However, it's also important to consider preference. While these findings indicate greater effectiveness using running, it's hard to know exactly why. If you hate running but enjoy cycling, this information isn't strong enough to warrant abandoning the exercise you enjoy.
After all, if you're more likely to actually exercise and put forth greater effort using a method you enjoy, that will likely be more effective than forcing yourself to do something you don't enjoy.
Why This Should Matter To You
It should matter because it sheds light on which form of exercise may be superior for losing body fat specifically. Further, it may also provide us with information regarding how important novel exercise is if you're looking to change, even as an experienced athlete. It also matters because it at least gives us an idea of which form of cardio may be more effective, allowing you to choose exercises that give you the most bang for your buck. This research is not definitive by any means but certainly provides another stepping stone towards objective exercise prescription.