Physiological benefits of aerobic training, also known as endurance or cardio, include improvements in tidal volume (amount of air moved by the lungs), blood volume, and stroke volume (amount of blood moved by the heart per beat). It also increases the number of capillaries, and the number and size of mitochondria. All of these contribute to the body’s ability to transport oxygen to the working muscle.

Recent research has shown that cardio, but not strength work or interval training, can make rodent brains bigger.

Okay, forget how much that last part sounds like the premise of a 1950s sci-fi movie. Let’s look at some other research.

One long-term study followed 1,583 middle-aged men and women with no personal history of dementia or heart disease for two decades. Before-and-after tests conducted 20 years apart showed that those who had stayed fit tended to have larger brains, while the unfit participants had lost gray matter.

Holding on to gray matter prevents cognitive decline and lowers the risk of dementia. However, no specific type of exercise was explored in that study.

And that’s a perfect introduction to the long-running debate about cardio and high-intensity interval training (HIIT).

HIIT fans always stack the deck

Let me be clear: I have nothing against high intensity intervals. I use them often in my own workouts and when I teach.

But something interesting happens when staunch HIIT proponents compare the relative benefits of HIIT to standard cardiovascular exercise.

They tend to cheat.

In the hands of die-hard HIIT fans, the word “cardio” has become code for boring exercise at lower intensity levels. It should come as no surprise that the benefits, if any, of such lame workouts fall far short of the benefits of HIIT.

And no one questions the criteria. So let’s challenge them with a few simple facts.

You can go hard and long

It is not true that intense training should involve short intervals of, say, 20 to 60 seconds. If you train well aerobically and seriously enough to achieve the aforementioned aerobic benefits, you can sustain a high level of work for quite some time.

Elite marathon runners, for example, run faster than a 5-minute mile pace for 26.2 miles. Most people would find it difficult, if not impossible, to run a single 5-minute mile. It’s a fast pace. Elite marathoners do it for a couple of hours.

As Matt Fitzgerald, noted marathon runner, trainer, and author of several books and articles, states, “Well-trained endurance athletes don’t really have to slow down much as they increase the duration of their efforts. We’re not the people who read magazines about elliptical trainers.”

Can’t we combine cardio with HIIT?

The training combination that appeals to me most fits with a series of about 8 intense intervals in a long workout of moderate to moderately high intensity.

However, it’s not just my personal preference. There is evolutionary evidence that this form of training is precisely what we were always meant to do.

In his book Born To Run, Christopher McDougall reveals the combination of morphology, paleontology, anthropology, physics, and mathematics that led to an understanding of how humans became the best distance runners in the animal kingdom.

There is no way this article can do justice to McDougall’s fascinating and detailed account of the rise of Homo sapiens over Neanderthals (they were parallel species) and the evolution of humans as supreme hunters hundreds of thousands of years before the creation of the tools we associate with hunting (spearheads, bows and arrows).

Some of the evolutionary changes include an upright posture to allow deeper breathing and limit retention of the sun’s heat; the ability to release body heat through sweat, instead of panting like other mammals until they must rest or die of hyperthermia; and the ability to speed up once the pursued animal has exhausted itself.

The human “persevering hunt” was mostly a combination of drag running, plus some short sprints. Humans evolved to run in conditions that no other animal can match, and it’s easier for us.

Good in endurance (for a long time)

Endurance athletes can usually continue into what is considered old age in other sports. In activities like distance running, they can still outperform teens or youngsters in their 20s to their mid-60s.

When workouts are always high intensity, there is likely to be overtraining, lack of full recovery, and a high incidence of injury.

Exhaustion after constant high-intensity work makes it feel like drudgery, rather than something to look forward to each day. Why not exercise in a way that you would enjoy in the long run?

Endurance athletes of other types show similar results. Master riders age 50 and up often outperform younger riders.

So the choice isn’t really between short, intense intervals and long, slow cardio with a magazine. The right kind of training includes both.

Cardio, of course, should be hard enough to cause a workout effect, not help you catch up on your reading.

That perfect combination is effective, enjoyable, sustainable in the long term, and totally in sync with our evolving nature.