New research from McMaster University says that periods of high intensity exercise aren't just good for your muscles, they're good for your memory.

Lead researcher Jennifer Heisz says the study showed a connection between six weeks of high-intensity workouts and improved memory.

The CBC's Conrad Collaco spoke with Heisz about her research. You can listen to or read our interview. Here's an edited and abridged transcript of that conversation. Click on the image at the top of the page to listen to the full interview.

Jennifer Heisz, department of kinesiology, McMaster University

Jennifer Heisz, an assistant professor in the Department of Kinesiology at McMaster, was the lead author of a study that connects high intensity training with improved memory. (JD Howell/McMaster University)

Describe the workout that you put your 95 test subjects through.

We had 95 younger adults who, before they started the study, weren't exercising. We enrolled them in a six-week, high-intensity interval training program. They would work out for 20 minutes. For one minute, they would be working out at a high intensity. For one minute, they were in a recovery mode. They'd alternate between these two states for 20 minutes.

They did this three times a week — Monday, Wednesday and Friday — for a six-week duration. Before and after this program, we measured changes in their memory. We also measured changes in their blood concentration of factors known to support brain health.

We found that one aspect of their memory — this ability to have a high fidelity memory with minimal interference — this type of memory, it improved with the exercise. - Jeremy Bensette , department of kinesiology , McMaster University

We found that one aspect of their memory — this ability to have a high fidelity memory with minimal interference — this type of memory, it improved with the exercise. We also found that a component in the blood called brain derived neurotrophic factor also increased in the individuals who responded the best to the exercise program.

We looked at how they improved in their aerobic fitness, and one thing that was surprising was that not everybody improved in their aerobic fitness. Some people, even though they were exercising, didn't respond to the program as we would have expected. These individuals, we call them low responders. The high responders had the greatest increase in this blood component known to support brain health. They also had the greatest increase in memory. They had a combined benefit.

McMaster University researcher Martin Gibala has a band new book about getting fit. 0:29

What do you think accounted for the people who showed little or no improvement in their aerobic fitness?

We think the exercise may have been too intense for them. They were all sedentary people at the beginning and we enrolled them in this relatively rigorous exercise. We know that exercise, in addition to its health benefits, does have create this immediate stress on the body. When the stress is too much, or when the body cannot adapt to that stress, stress hormones like cortisol can build up in the system and this impedes the production of that blood component.

If the intensity was the problem, we're recommending that individuals start at a lower intensity and then gradually progress through the program.

Why did you pick high-intensity workouts as the base for the fitness test for the study?

It is such a powerful stimulus. It's very intense. It's for physiological and psychological adaptations. Because our study was only six weeks long, we wanted to be sure we had a strong enough exercise response to see changes. With that said, it could have been too intense for some people. So backing off the intensity would be a good strategy for people who start an exercise program and feel this is causing more fatigue than making me feel better.

What makes you think this type of exercise might benefit people with Alzheimer's or dementia?

With aging, we know there is a loss of memory in particular with dementia and Alzheimer's disease. The hippocampus, which is the brain region involved in learning and memory, is most affected. The type of memory we saw improved in young adults was memory that really relies on the hippocampal brain region. That blood component, brain derived neurotrophic factor (BDNF), is low in people who have Alzheimer's or dementia.

We're thinking that if we can use exercise to increase BDNF to improve this memory, then it may help individuals with dementia and Alzheimer's. In a follow up study to this one, we have run older adults through the same protocol. Preliminary results suggest that we get the same positive benefits to memory, but this is not yet published.