One of the most common questions I receive as a coach is, “Is steady state or interval training better for cardio?” In a recent Journal of Strength and Conditioning Research article, investigators sought to find the answer.
Study Design
In the study, researchers used exercise bikes to figure out what sort of energy and how much was consumed during various protocols. Each of thirty participants performed one of three cycling routines. Each of the routines had the same total power output. What changed was the degree to which the power fluctuated over the course of their workout.
- Group One: This group maintained a steady 75 watts on the bike, with no variation, for thirty minutes.
- Group Two: The second group alternated between fifty watts and 100 watts every five minutes for the same amount of time.
- Group Three: The final group switched between 25 and 125 watts every five minutes.
So the duration was the same between all three groups, and theoretically the energy required would also be pretty similar. Each group was tested for their oxygen uptake and the amount of fat and carbs they burned during each protocol. After each session, the researchers continued to test these values for a further 25 minutes during rest.
Results
For oxygen consumption, the groups varied, as you might expect. The steady-state group maintained a steady oxygen consumption that dropped at rest. The other two groups had peaks and valleys in their oxygen consumption, corresponding with the changes to intensity.
As such, the group that went up to 125 watts had the greatest peaks but also the greatest valleys. The oxygen consumed during exercise was the same for each group. This probably means that energy consumption was pretty much the same.
During the recovery period after the training the two groups with intensity variation consumed more oxygen, and thus used more energy. While this amount was reported by the researchers to be statistically significant, it amounted only to about .75 milliliters more oxygen consumed each minute than the steady-state group. For the average person, this amounts to about a quarter of a calorie. Significant, perhaps, but not substantial.
Carbohydrate consumption was pretty even between the steady group and the 100-watt group. The latter had peaks and valleys as you might expect, but the total carb consumption was similar. However, carbohydrate consumption was substantially higher in the 125-watt group. The subjects in that group probably crossed over into anaerobism markedly and thus experienced a substantially higher carb consumption. During recovery, the 125-watt group also burned more carbs, but this was only in the first ten minutes post workout, after which the rates became roughly the same.
Fat burning was essentially the inverse of the carb consumption. The steady group burned the most during exercise, with very similar values for the 100-watt group, followed way behind by the 125-watt group. The researchers indicated that the recovery period experienced similar fat burning values, but the 125-watt group appeared to be increasing fat utilization by the end of the test period. I’d be curious what happened beyond that.
So, there you have it. When people ask which is superior between intervals and steady state cardio, the answer is: it doesn’t matter much. The two major things to consider are first, that substrate utilization differs between the two, which can alter hunger afterward and cause you to overeat, and second, the researchers didn’t measure perceived intensity, but steady state is much more tolerable and can be maintained for longer. As such, I find my typical recommendation of steady state cardio to be supported by this study.
References:
1. Jie Kang, et. al., “Acute Effect of Intensity Fluctuation on Energy Output and Substrate Utilization,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000533
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