On the internet you’ll see people divided up about cardio:
“All you need is interval training. It makes you better at everything!”
“No, steady state is just what the doctor ordered. Good for your heart.”
Well, as you know from my articles, the truth is usually somewhere in the middle, and so it is in this case.
In this article, I’m going to teach you:
- The physiological effects of interval training
- The physiological effects of steady state
- When it makes sense to use each one
But first, let’s get the definitions out of the way
Both interval training and steady state are forms of cardio, but performed differently. With interval training, you “go” hard. Typically, the “hard” part is 15 seconds, to 2 minutes, and that’s followed by an “easy” recovery period of anywhere from 30 seconds, to 3 minutes, or more.
With steady state, you maintain a more or less even speed for at least 15 minutes or longer.
The mode or activity is irrelevant. You can run, cycle, row, swim, etc.
The Physiological Effects of Interval Training vs. Steady State Training
At the cardiovascular level, one study found that interval training increases stroke volume by about 10% more, compared to steady state training, when done over 8 weeks. Wait, what? What’s “stroke volume”, you ask? It’s the amount of blood that your heart pumps with each stroke. For the average person (the average person is about 70 kg, or 154 pounds), it’s about 70 mL.
Another study found that interval training increases the strength of the contractions of the heart muscle by 13% (that’s called “cardiac contractility”). That’s on par with steady state training. But it does take less time.
At the level of the muscle, research is finding that interval training is far superior to steady state at increasing the total number, and efficiency of the mitochondria. What? Mitochondria? What’s that? If you think back to high school biology, they call “mitochondria” the “powerhouse of the cell.” It basically gives you energy by burning fat and glucose.
Every muscle cell has several mitochondria, and those mitochondria have enzymes (proteins that speed up reactions in the body). So with both interval training, and with steady state, there are two effects:
- The number of mitochondria increases
- How hard the enzymes are working also increases
But both of those factors happen to a much greater extent in interval training, compared to steady state.
In fact, in one study, the group that did steady state training had to exercise 5 days per week, for 40-60 minutes, at an intensity of 65% of their maximal aerobic capacity to get the same results as the interval group did exercising 3 days per week, for 4-6 intervals of 30 seconds, at maximum intensity (with 4.5 minutes in between intervals). How’s that for efficiency?
So it seems that there’s a tradeoff between duration and intensity. The “price” you pay for saving time on your exercise is hard work. But short work.
There is, however one area where steady state training is clearly superior: maximal cardiac output. What is that? That’s the most amount of blood that the heart can pump in a minute.
In one study, interval training was compared to steady state training, and it was found that the participants doing intervals didn’t increase maximal cardiac output, but the steady state group did.
When to Use Each One: Intervals vs. Steady State
So it seems that in almost every parameter, intervals are superior to steady state. So does that mean you use intervals all the time, and forget about steady state? No.
They are both tools in the toolbox, and just like with anything, there’s no “good” or “bad”, there’s only correct application.
So what is the “correct application” for intervals? There are several.
If you’re the average person, without athletic goals, and without competitive goals, just looking to be in good shape, and you don’t feel like putting in 5-6 days of exercise per week, you can probably use interval training exclusively. As you see from the research, 2-3 days per week gets you a lot of “bang for your buck.”
Alternately, if you’re an athlete, and you’re in a “stop and go” sport (not pure endurance, and not pure strength/power. Examples would be basketball, soccer, hockey, etc.), intervals are a must, because your sport is an interval sport by nature.
And even if you are a pure endurance athlete, there’s a time and a place for intervals. What is that time and place? You’re basically limited by your maximal aerobic capacity. A person can maintain the speed that corresponds to their maximal aerobic capacity for about 6 minutes. But what if you could increase your maximal aerobic capacity? Then you could perform better at your (endurance) sport.
However, how do you raise your aerobic capacity, when the longest that you can go at your max is 6 minutes? Do you do 6-minute workouts? No. You do interval training.
So you run at the speed corresponding to your max for say, 3 minutes, and then you run at a slower speed for another 2-3 minutes. Do 3-10 repeats of that, and now, you’ve accumulated 9-30 minutes at your maximal aerobic capacity. Something you couldn’t do if you just ran until exhaustion, because exhaustion would happen in about 6 minutes.
So that’s the “correct application” for interval training. Now, what’s the correct application for steady state training? There are also a couple uses for it.
For one thing, if you are recovering from soreness or from difficult exercise the day before, lower intensity exercise is superior to both high intensity, and no exercise. It improves blood flow and circulation, without being too stressful on the body.
Additionally, if your sport in and of itself is a pure endurance sport, you’ll need to do steady state training.