How to Use Exercise to Improve Your Brain’s Health, Longevity & Performance

The episode sets out to connect exercise with three related outcomes: brain health, brain longevity and brain performance, defined as the ability to learn new information over long periods of time and into old age. The host separates two time frames. Acute effects show up in the minutes, hours and day of a workout. Long-term effects build over the days, weeks and months afterward. For people who exercise regularly, the host says these effects on brain health and performance compound over time.

The host describes the research base as very large: "literally tens of thousands of studies on this topic," plus meta-analyses and reviews, which he says all point to positive effects of various exercise types on the brain. Because those studies use many different protocols, the stated aim is to organize them into a framework built on specific neurobiological and endocrine mechanisms. Listeners could then adjust an exercise program to the time they have, their age, their health status and the brain changes they want. The host also presents the topic as a way to understand how the body and brain communicate with each other all the time, not only during exercise.

Most peer-reviewed work on exercise and the brain covers two categories: cardiovascular exercise and resistance training. Cardio ranges from short, high-intensity efforts to longer, lower-intensity sessions. The short efforts are all-out bouts of 30 seconds, 60 seconds, or sometimes two or four minutes, followed by rest. The longer sessions run 20, 30, 45 or even 60 minutes at a steadier, lower intensity.

The host says most studies in this area focus on cardiovascular exercise. Early studies mostly used 30 to 60 minutes of lower-intensity exercise that still raised heart rate. More recent work focuses on high-intensity interval training, and some studies use sprints as short as six seconds followed by rest and repeated several times.

Resistance-training studies use either compound, multi-joint movements such as squats, deadlifts, bench press, shoulder press and dips, or single-joint isolation exercises. A common laboratory choice is the seated single-leg leg extension. The host admits this can seem like a strange choice, then gives the researchers' reasons, which he heard from scientists who do this work. Most people can do the movement with little instruction. It can be done fairly safely by non-athletes, including people over 65 without much athletic background. The untrained leg also serves as a within-subject control when comparing strength gains.

The host argues these minimal protocols are still informative and may even mark "the lower threshold for the amount of resistance training and type of resistance training that could benefit the brain." Other studies use compound lifts with free weights. The host notes that the best studies are tightly controlled and done in a lab in a set way. Some recruit untrained subjects and others trained subjects, and each choice comes with caveats.

The host warns that the discussion will often pool results across these different exercise types, durations and intensities. Where a specific exercise is linked to a specific, especially beneficial brain change, he says he will point that out. Studies generally test one of two kinds of change. Acute studies have people exercise and then take a cognitive test or another measure of brain health and performance. Chronic studies track changes over longer periods, usually with exercise two to four times a week (most often three) for four weeks to six months. These designs reflect what is practical in controlled lab research.

The host admits that this spread of study types and variables can look like a "huge ball of barbed wire." He promises to make it clear and actionable.

The host's first main claim is that "most all of the studies" in this literature find positive effects. As an example, he cites data showing that six maximal six-second sprints on a stationary bike, each followed by one minute of rest, produce significant acute improvements in brain performance. The tests in these studies include memory tasks and the Stroop task, a cognitive flexibility test in which people must tell apart the color a word is printed in from the word itself.

Steady-state cardio lasting 20 to 30 minutes, such as running, rowing, swimming or stationary cycling, also significantly improves performance. The tasks used include working-memory tests like remembering a short string of numbers, math problems, and the Stroop task. The host says the many different tasks "reveal the same thing."

This leads to a counterintuitive conclusion. On overall measures, such as the percentage of information learned, the host says the sprint protocol and the 20-minute cardio session "really doesn't make a difference." He makes a clear distinction here. The workouts affect the body very differently. High-intensity, short-duration exercise affects VO2 max and circulating hormones and neuromodulators differently from long, low-intensity exercise. Leg extensions and 10 sets of 10 squats also produce very different physical adaptations. Yet in every acute study, the host says, brain output and function increase significantly afterward.

To explain why such different workouts give similar acute benefits, the host proposes one mechanism and immediately limits it:

And the answer is arousal. However, the answer isn't entirely arousal, meaning not all of the positive effects of exercise on brain health, longevity, and performance can be explained by arousal.

He then gives a rough share. Stepping back from the literature, he says "probably 60% to 70% of the effects of exercise on brain health, performance, and longevity can be explained by the specific shifts in our physiology" during exercise, in the body and directly in the brain. He identifies that shift as increased autonomic arousal, which happens during exercise and continues for a window after it ends. The host offers this figure as his own overall judgment of the literature ("I think it's fair to say"). It is not presented as the result of a specific study. The plan is to cover arousal and acute performance first, then move to chronic effects over hours, days, weeks and years.

The host argues that arousal is "not trivial." He says understanding it also helps explain deliberate cold exposure, stress and trauma, and helps in designing a program that gives the most benefit to both body and brain.

To support the arousal–learning link, the host reviews a paper from Larry Cahill's group at UC Irvine titled "Enhanced Memory Consolidation with Post-Learning Stress: Interaction with the Degree of Arousal at Encoding." He describes it as one of several papers from that group.

Autonomic arousal is defined as more activity in the sympathetic arm of the autonomic nervous system: more alertness, wide eyes, readiness to move, and higher heart rate and blood pressure. The host calls this a good state for learning, "provided it's not too much alertness, too much arousal." He says the paper shows it is also a good state to be in after exposure to material one wants to learn.

The way these studies raise arousal matters for how the evidence is read. They do not use exercise. They use the cold pressor test, in which people put an arm in ice water for one to three minutes, which quickly and significantly raises circulating cortisol. In other studies, participants receive a drug injection that raises adrenaline (epinephrine) and sometimes cortisol. The host notes that cortisol is involved in the stress response but does other things too. The conclusion he draws across these studies is:

elevations in autonomic arousal after one is exposed to information increases one's memory for that information and one's memory for the details of that information.

The featured study also compared emotionally laden and neutral information. The host does not go through those details. He says other work from this and other labs has repeatedly linked higher cortisol, adrenaline or norepinephrine (which he calls the brain's analog) to better memory for information and its details. Higher arousal is also often linked to a better ability to use that information to come up with new ideas or to think about it logically in new ways.