Exercise and the Brain

As noted earlier, mitochondrial degradation is a primary culprit in dwindling muscle mass. But recent evidence indicates that exercise can slow down this effect. According to Mark Tarnopolsky, a professor of pediatrics and medicine at McMaster University in Hamilton, Ontario, resistance training activates a muscle stem cell called a satellite cell. In a physiological process known as ‘gene shifting,' these new cells cause the mitochondria to rejuvenate. Tarnopolsky claims that after six months of twice weekly strength exercise training, the biochemical, physiological and genetic signature of older muscles are "turned back" by a factor of 15 to 20 years. That's significant — to say the least.

Studies involving middle-aged athletes indicate that high intensity exercise protects people at the chromosomal level as well. It appears that exercise stimulates the production of telomerase, what allows for the ongoing maintenance of genetic information and cellular integrity. Exercise also triggers the production of antioxidants, which boosts the health of the body in general.

And indeed, other studies are successfully linking athleticism to longevity. A recent analysis published in Deutsches Ärzteblatt International of more than 900,000 athletes (ranging in age from 20 to 79) showed that no significant age-related decline in performance appeared before the age of 55. And revealingly, even beyond that age the decline was surprisingly slow; in the 65 to 69 group, a quarter of the athletes performed above average among the 20 to 54 year-old group.

Essentially, exercise helps the body regenerate itself. This likely explains why older athletes are less susceptible to age-related illnesses than their sedentary counterparts. Moreover, ongoing exercise has been shown to preserve lean tissue, even during rapid and substantial weight loss. It also helps to maintain strength and mobility, which can significantly reduce risk of injury and stave off health problems that would otherwise linger.

Even more remarkable is how resistance training can stave off cognitive decline — what is arguably just as important as physical well being. In a study led by Teresa Liu-Ambrose of the University of British Columbia, women between the ages of 70 and 80 who were experiencing mild cognitive impairment were put through 60-minute classes two times per week for 26 weeks. They used a pressurized air system (for resistance) and free weights, and were told to perform various sets of exercises with variable loads. The results were remarkable: Lifting weights improved memory and staved off the effects of dementia. It also improved the seniors' attention span and ability to resolve conflicts.

With your talents and industry, with science, and that steadfast honesty which eternally pursues right, regardless of consequences, you may promise yourself every thing—but health, without which there is no happiness. An attention to health then should take place of evey other object. The time necessary to secure this by active exercises, should be devoted to it in preference to every other pursuit.

Past experiments have shown persuasively that exercise spurs the birth of new mitochondria in muscle cells and improves the vigor of the existing organelles. This upsurge in mitochondria, in turn, has been linked not only to improvements in exercise endurance but to increased longevity in animals and reduced risk for obesity, diabetes and heart disease in people. It is a very potent cellular reaction.

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Like muscles, many parts of the brain get a robust physiological workout during exercise. “The brain has to work hard to keep the muscles moving” and all of the bodily systems in sync, says J. Mark Davis, a professor of exercise science at the Arnold School of Public Health at the University of South Carolina and senior author of the new mouse study, which was published last month in The Journal of Applied Physiology. Scans have shown that metabolic activity in many parts of the brain surges during workouts, but it was unknown whether those active brain cells were actually adapting and changing.

To see, the South Carolina scientists exercised their mice for eight weeks. The sedentary control animals were housed in the same laboratory as the runners to ensure that, except for the treadmill sessions, the two groups shared the same environment and routine.

At the end of the two months, the researchers had both groups complete a run to exhaustion on the treadmill. Not surprisingly, the running mice displayed much greater endurance than the loungers. They lasted on the treadmills for an average of 126 minutes, versus 74 minutes for the unexercised animals.

More interesting, though, was what was happening inside their brain cells. When the scientists examined tissue samples from different portions of the exercised animals’ brains, they found markers of upwelling mitochondrial development in all of the tissues. Some parts of their brains showed more activity than others, but in each of the samples, the brain cells held newborn mitochondria.

There was no comparable activity in brain cells from the sedentary mice.

This is the first report to show that, in mice at least, two months of exercise training “is sufficient stimulus to increase mitochondrial biogenesis,” Dr. Davis and his co-authors write in the study.

Scientists have discovered that lactose, a byproduct of intense muscular activities, can be used to fuel the brain with energy. When glucose, the natural fuel of the brain, is no longer present in sufficient quantities, the cell tissue can “switch” to alternative energy, to prevent any damage to the brain on account of the lack of energy.

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Consequently, by consuming the lactose in the blood, the brain clears the way for glucose, the main powering substance in the body, to reach the muscles and provide them with energy for the hard work they are doing. This research is very important because it explains why the brain is able to operate even when the body demands unusually high amounts of energy and oxygen. In fact, our mind actually goes into a higher “gear,” in order to be able to cope with any situation.

Lactate is a dynamic substrate with great potential as an energy source in sports drinks. To date, however, the efficacy of adding lactate to these drinks has been sparsely assessed [5,15,16]. Lactate was once considered a metabolic waste but is now recognized as an important energy substrate in the body. Lactate is the main product of carbohydrate metabolism and can be used as a fuel in working muscle cells shuttled to other tissues such as the heart where lactate is fuel [17], or to the liver were lactate serves as a gluconeogenic precursor [18].

Scientists are also encouraged by studies on mice with a certain genetic mutation that makes them age prematurely — complete with graying and thinning fur, cataracts, hearing loss, smaller brains, enlarged hearts, anemia and thin and weak muscles — hallmark symptoms of growing older. To test whether it was possible to slow or reverse the process in these mice, a team led by Dr. Mark Tarnopolsky, a professor of pediatrics and medicine at McMaster University in Ontario, Canada, had the rodents exercise on treadmills three times a week from the age of 3 months to 8 months (about ages 20 to 55 in human terms).

In a 2011 study in the journal Proceedings of the National Academies of Sciences, the researchers showed that the exercise prevented many of the physiological symptoms of aging as well as premature death in the mice — to the point where they were indistinguishable from non-genetically altered mice.

"We protected not just the muscles — which people conceptually would say, 'Well, yeah, it makes sense that if you run, your muscles will be protected' — but even their cataracts, their kidneys, their gonads," Tarnopolsky says.

Similar results can be seen in humans. For 21 years, researchers at Stanford University have studied the effects of consistent exercise on 284 runners 50 and older. In a 2002 article in the Archives ofInternal Medicine, they reported that — 13 years into the study — a control group of 156 similar people who exercised much less on the whole than the runners had a 3.3 times higher death rate than runners as well as higher rates of disabilities.

In a 2008 study in the same journal, they reported that after 19 years, 15% of runners had died, compared with 34% of the control group. After 21 years, runners had significantly lower disability levels than non-runners; their death rates from cardiovascular events, cancer and neurologic disorders were much lower than in non-runners — 65 of the runners had died of cardiovascular, neurologic and cancer events compared with 98 deaths in the control group.

"You're 100 times better … as an athlete training in your 40s and 50s than a sedentary person in your 20s, any way you look at it," Tarnopolsky says.

• Motor neurons die, particularly from age 60 onward. This causes connections between muscle fibers to wither — and that, in turn, eventually leads to loss and shrinking of muscle fibers. As a result, muscles get smaller and a person gets weaker, says Sandra Hunter, an associate professor of exercise science at Marquette University in Milwaukee. "Physical activity can offset some of that," she says. "But there is this biological aging process going on — the neurons will die regardless of how fit you are."

• Some types of muscle are lost more quickly than others. You'll lose comparatively more fast-twitch muscle fibers (those that fire quickly and are used in activities like sprinting) than slow-twitch muscle fibers (those that contract slowly and use oxygen efficiently, making them useful for endurance activities). Slow-twitch fibers are lost more slowly because they're called on more often in everyday activities. The plus side of this: Even though aging adults have less muscle mass, their higher proportion of slow-twitch, fatigue-resistant muscle fibers can give them a leg up in endurance activities such as running or cycling.

• Beginning in the late 30s, maximal oxygen consumption, or VO2 max, decreases at a rate of at least 10% per decade, or about 1% per year, in most people other than highly trained athletes. VO2 max is dependent on heart rate, which decreases by about 5 to 10 beats per minute per decade. This reduction in aerobic capacity is one of the reasons for a decline in endurance performance with age. "You can't send as much blood and oxygen to the working muscles, and the pace slows down," says Jason Karp, a running coach based in San Diego. Hard aerobic training can offset the decline in VO2 max — up to a point.

• With age, large, elastic arteries including the aorta (which shuttles blood from the heart) and the carotid artery (which feeds blood to the brain) get stiffer. As a result, blood pressure rises and the heart has to work that much harder. In addition, the inner lining of arteries, called the vascular endothelium, loses certain functions: Signals that normally open the arteries and increase blood flow or narrow the arteries to reduce blood flow are not operating properly. As a result, the artery remains in a relatively narrow state, contributing to cardiovascular disease, says Douglas Seals, a physiologist at the University of Colorado at Boulder. Beyond the health ramifications, he adds, "if the arteries do not vasodilate robustly in response to these signals, then they cannot increase blood flow appropriately to meet the demands of increased energy metabolism of the exercising muscles — and performance will be limited."

• Wear and tear builds up on the joints. Connective tissue becomes less elastic, and lubricating fluids decline, making aging athletes more injury-prone. Cross-training — doing a mix of high- and low-impact exercises such as weight training, yoga and cycling — works different muscle groups and can reduce the risk of orthopedic injuries from overuse, says Michael Joyner, a professor of anesthesiology and an exercise researcher at the Mayo Clinic in Rochester, Minn. And (though research is limited) studies suggest that a lifelong exercise habit helps keep joints intact. In part, this could be because activity improves blood flow and other regenerative pathways and may activate stem cells that help the body repair itself, Joyner says.