We all know that exercise is good for us. It lowers the risk of cardiovascular disease and diabetes, helps control weight, preserves muscle, and, importantly, helps maintain independence as we grow older. I have written often about the importance of both aerobic exercise, such as brisk walking, swimming, or cycling to maintain cardiovascular fitness, and resistance exercise to maintain muscle mass and strength as we age.

But there is another form of exercise worth adding to the discussion: high-intensity interval training, or HIIT.

The concept is simple. Imagine you are riding an exercise bike in the gym. You pedal at a moderate pace for about 2 minutes, then you increase the resistance and pedal as fast and hard as you can for 30 seconds. You will likely sweat and your leg muscles will start to burn. You then revert to the slower, easier pace for 90 seconds and then repeat the high intensity/low intensity duo for a total of 8 rounds with a few minutes of cool down at the end. The total time elapsed is about 20 minutes and just 4 minutes of intense exercise.

My colleague Harry Oken, MD and I wrote about this interval exercise approach in our book BOOM — Boost Our Own Metabolism. At the time, one reason for our interest was evidence that intense exercise, especially early in the morning, could produce a substantial increase in human growth hormone and other metabolic responses. Another was that just a few minutes of high intensity achieved the same benefits of a much longer Zone 2 type of exercise. HIIT is a good way to maintain or increase your V02max, a known longevity positive.

There is a just published study in Cell Reports Medicine that looks much more deeply at what is happening in the body during HIIT. Led by Dr. Paul Cohen and colleagues at Rockefeller University, they found that the multiple organs, not just muscle, immediately produces many proteins that reach the blood stream and travel to other organs, call it organ cross talk.

The researchers compared two very different forms of exercise. One group cycled continuously at moderate intensity for 90 minutes. The other performed six 30-second all-out cycling sprints, separated by recovery periods as described above. Consider that this amounted to just three minutes of actual high-intensity exercise and a total of 11 minutes of total time plus the warm-up and cool-down periods.

The difference in what happened inside the body was remarkable.

The researchers measured nearly 2,900 proteins circulating in the blood. Immediately after the sprint exercise, 714, nearly one-quarter, had changed significantly, all but a few having increased substantially. Within a few hours, the protein levels had largely reverted to baseline. But in the group that did only moderate intensity cycling for 90 minutes, only seven protein levels had changed immediately.

The exerkines did not derive only from the exercised muscle, but multiple other organs including adipose, liver, immune, pancreas, intestine, and brain cells.

The researchers then went to large United Kingdom biobank databases and found that the sprint-altered proteins tended to be those connected to a reduced risk of cardiac and metabolic diseases/disorders including type 2 diabetes, obesity, and cardiovascular health. Interestingly, some of the proteins released by sprint exercise correlated with proteins in the Biobank that are associated with a decrease in biologic age.

Think about that. Three minutes of extremely vigorous exertion triggered an enormous molecular response throughout the body, but 90 minutes of moderate paced exercise did not. More importantly, those sprint derived exerkines were associated with markers of better health and a lower biologic age.

Your muscles are talking to the rest of you

We used to think about exercise largely in mechanical terms. The heart pumps faster. The lungs move more air. Muscles contract and burn fuel. Do that repeatedly and the heart and muscles become stronger. But as I have written previously, resistance exercise causes muscles (and other organs) to release chemicals (proteins, peptides, metabolites, and other signaling molecules) that travel to other parts of the body and generally have a positive effect on other organs’ cells. Instead of calling them the usual name of cytokines, meaning released by the cell, it has become customary to call them exerkines instead. By whatever name, they are metabolically active and impact the metabolism of other cells.

The Rockefeller study found evidence of communication involving muscle, fat, the liver, immune system, gastrointestinal tract, pituitary gland and even the brain. High-intensity exercise appears to send out a particularly powerful burst of these molecular messages.

Some of the proteins stimulated by intense exercise were associated, in large population databases, with lower risks of metabolic and cardiovascular disease. Others were associated with biological aging. The study does not prove that changing these proteins prevents disease or extends life, the investigators themselves are careful not to make that claim, but it offers an intriguing explanation for why relatively brief periods of vigorous exercise can produce substantial health benefits.

Instead of thinking about one hormone or one metabolic pathway, we can now begin to see intense exercise as producing a coordinated, body-wide response. Muscles do not simply become stronger. They communicate. Other organs listen and respond. That may help explain why exercise has effects seemingly far removed from the muscles doing the work.

HIIT and the aging body

This becomes especially important as we age. One of the most useful measurements of cardiovascular fitness is VO₂ max, essentially the maximum amount of oxygen the body can use during strenuous exercise. VO₂ max tends to decline with age, and a low level eventually has very practical consequences. Walking rapidly through an airport, climbing a flight of stairs, carrying groceries, or keeping up with grandchildren becomes increasingly difficult.

HIIT is particularly effective at improving VO₂ max. Studies of older adults have found that interval training can produce substantial improvements in cardiorespiratory fitness, in some studies greater than those achieved with continuous moderate exercise.

That reserve capacity matters. Independence in old age depends not merely on being able to perform today’s activities, but on maintaining enough physiological reserve to continue performing them years from now.

There may also be benefits for the brain. Exercise improves cerebral blood flow and stimulates biological pathways involved in neuroplasticity, the brain’s ability to adapt and maintain connections. Studies of HIIT in older adults have reported improvements in aspects of executive function, working memory, and attention, although the evidence is still developing. There is reason to believe that HIIT done regularly for many months reverses some of the losses of aging in the brain, both in the cortex and the hippocampus, slowing or even reversing some of the declines in normal cognitive aging and lowering the risk of dementia, but these are as yet unproven. We can say that maintaining cardiovascular fitness and remaining physically active are important components of maintaining brain health.

But HIIT does not mean sprinting

Here an important caution is necessary, especially for older adults.

The Rockefeller participants performing six all-out sprints were young, healthy adults. I certainly would not recommend that an 80-year-old who has been sedentary climb onto a bicycle tomorrow and attempt six or eight maximal 30-second sprints.

“High intensity” is relative. Someone who has been sedentary or who has cardiovascular, pulmonary, or significant muscle loss should discuss vigorous exercise with their physician, and if approved, begin under the guidance of a personal trainer or physical therapist. The objective is not exhaustion. It is to periodically ask the cardiovascular and metabolic systems to work substantially harder than they do during ordinary activity, followed by recovery.

Don’t give up your walk or your weights

HIIT should not replace other exercises. Continue walking. Continue cycling, swimming or whatever aerobic activity you enjoy. And especially as you grow older, include resistance exercise at least twice a week. Muscle mass and strength are essential for getting out of a chair, climbing stairs, maintaining balance, and preventing frailty. These are the essential elements of retaining independence.

Think of high-intensity intervals as an addition, a very useful addition. Once or twice a week, if your health permits and your doctor agrees, consider adding a few brief periods during your usual aerobic exercise when you substantially increase the intensity and then recover. As fitness improves, the duration or number of intervals can gradually increase.

The remarkable message from the Rockefeller study is that our bodies notice the difference.

Three minutes of intense exertion caused hundreds of proteins and metabolites to change, initiating communication among organs throughout the body. We are only beginning to understand what all those molecular conversations mean. But they reinforce something we already know. Exercise is among the most powerful medicines available to us. As we age, the goal is not to become an athlete. The goal is to preserve enough strength, cardiovascular capacity, balance, and brain function to continue doing the things that make life enjoyable. And most importantly, it is to maintain independence.

Walking matters. Strength training matters. And now we have a reason to pick up the pace.

It suggests to me, and as Dr Oken I wrote in BOOM — Boost Our Own Metabolism, a regular program of HIIT, once or twice a week for just 20 minutes, is beneficial to our health. At age 84, I plan to redouble my efforts to do it at least once a week, maybe two.

It is never too late to start and sometimes it pays to go a little faster.