Just Doing it

by Jon Nalick

Hippocrates, the Greek physician widely regarded as the founder of medicine, knew what he was talking about when he said, "Eating alone will not keep a man well; he must also take exercise."

In fact, physicians and researchers believe that this 2,400-year-old prescription for a long and healthy life is more important today than ever before because our sedentary ways are quickly turning us
into a nation of couch potatoes and desk jockeys.

Already one-third of Americans are considered overweight and the primary culprit, along with a high-fat diet, is a chronic lack of exercise. Even more alarming, a 1996 Surgeon General's report suggests that as many as 200,000 Americans each year die prematurely due to causes directly attributable to inactivity.

Kelvin J.A. Davies, Ph.D., D.Sc., professor of gerontology, biochemistry and molecular biology and director of the USC Gerontology Research Institute, says evolutionary pressures have produced a human body optimized specifically for a life requiring frequent strenuous activity. Up through the beginning of the Industrial Revolution, humans had to exert themselves physically-toiling in the fields to grow food, pursuing prey-to survive. Only in the past 100 years or so has a sizeable percentage of the population found its sole exertion in getting food to be opening a refrigerator door.

"As organisms, we're adapted for a very active lifestyle-the human body needs exercise. If you don't maintain that active lifestyle, you pay a high price in terms of diminished function," and health problems such as cardiovascular disease and diabetes, Davies says. "When it comes to your body's fitness, the adage 'use it or lose it' really is true."

Robert Wiswell, Ph.D., associate professor of biokinesiology and physical therapy, says that regular, vigorous exercise boosts the metabolism and immune system, improves mood, helps shed unwanted pounds, builds muscles, moderates blood sugar, reduces cholesterol, strengthens the heart and staves off an early death.

How exactly the simple acts of running or lifting weights can contribute so much to health is currently the subject of much scientific study and debate, and although the exact mechanisms at work are not always understood, the benefits are hard to overstate, Wiswell says.

When challenged with any physical task, the human body responds by activating the musculoskeletal system and then marshals the cardiovascular and respiratory systems as needed to sustain the activity.
When the body engages in exercise several times a week, each of these physiologic systems undergoes specific adaptations to increase the body' efficiency and capacity. The magnitude of these adaptations depends primarily on the intensity and duration of the training sessions, the force or load used in training, and the body's initial level of fitness, Wiswell says.

Perhaps the most important consequence of regular exercise is its beneficial effects on the cardiovascular system. Regular exercise can strengthen the heart muscle and increase by as much as 30 percent the volume of blood pumped with each heartbeat, especially at moments of peak exertion.

At the same time, physical training increases the blood volume by more than 10 percent, with a concomitant increase in the ability to convey oxygen throughout the body. The stronger heart muscle is also more efficient, able to do more work with less strain and at a lower blood pressure. For people with normal blood pressure (around 120/80), slight decreases in their blood pressure are common following regular exercise. For those with high blood pressure (over 140/90), decreases in their systolic and diastolic readings average about 10 mm Hg and eight mm Hg respectively.

For the musculoskeletal system, endurance training increases the cross sectional area of muscle fibers and increases the number of capillaries to boost the active muscles' blood supply. Strength or resistance training, such as weight lifting, can also boost the size and number of muscle fibers. And both kinds of exercise increase the size and the number of mitochondria-the cell's energy factories-in muscle cells and bolsters their efficiency.

Further, the myoglobulin content of muscle rises with increased physical activity, boosting muscles' ability to store oxygen. Glycogen storage rises as well, giving muscle cells an improved ability to burn fat for fuel.

Wiswell says evidence suggests exercise can prompt an increase in HDL, known commonly as "good cholesterol," which is a key mechanism in removing potentially life-threatening plaques from building up on arterial walls. "There also seems to be a direct relationship between exercise and the blood clotting factor fibrinogen, a blood component that allows you to clot easily. Physically active men and women are suspected to have a lower clotting factor-their blood is less sticky," which leaves them
at lower risk for strokes and heart attacks, he says.

Physical exertion also plays an important role in the regulation of blood sugars-which is why regular exercise is crucial for diabetics. "There's good evidence that active people have lower glucose and insulin levels when at rest, and they seem to have a much easier time maintaining a healthy level of glucose in the blood," Wiswell says. USC epidemiologist Ruth K. Peters, Sc.D., professor of preventive medicine, adds that exercise also appears to help prevent the development of type II diabetes.

"For a long time it wasn't thought that exercise was an important factor in preventing diabetes, but recent studies show that sedentary people have about a 50 percent greater risk of developing type II
diabetes than those who regularly engage in vigorous exercise," she says. Exercise helps prevent obesity and reduce fat-especially abdominal fat that is associated with heart attacks and type II diabetes. "In fact it seems that almost every time you examine the effects of regular physical activity, you find something new about how useful it is," Peters adds.

For example, she notes that although the exact mechanism remains unclear, exercise appears to protect people against certain kinds of cancers, most notably cancers of the colon and breast. Studies show that very sedentary people are as much as twice as likely to get such cancers than fervent exercisers.

Another striking example is the consistent finding in study after study that exercise has a profoundly positive effect on mood and a person's sense of self-worth, and helps decrease anxiety and depression. Some studies even show that exercise can significantly reduce the risk of suicide.

"There's no question that regular exercise boosts measures of self concept, such as self-esteem or self acceptance-it's one of the most consistent findings in exercise literature. We don't know if the improvement is due to a sense of personal accomplishment or something more physical, for example, involving brain levels of certain neurotransmitters," Peters says.

S. Victoria Jaque, Ph.D., assistant professor of biokinesiology and physical therapy, says that under normal circumstances, the body continually grows and reabsorbs bone in a fairly stable ratio.
Physical stress on the skeletal system seems to alter the ratio slightly so that more bone is formed than reabsorbed. As a result, exercises, especially those that place greater than normal physical loads on the skeletal system, can boost bone density by a small, but significant amount.

"The gains are usually only one to three percent, but that can be enough for some people-especially those with osteoporosis, or brittle bones-to become less vulnerable to fractures. It can be very beneficial," she says.

Humans tend to reach peak bone density in their teens and 20s, then slowly lose bone mass in the decades that follow. Studies show that exercise during and just after puberty can boost an individual's peak bone mass, with potential health benefits for the rest of their lives.

"If you exercise during those years, you have a little more bone to lose-a little more of a cushion-compared to someone who doesn't," Jaque says. She says that exercise with weights or activities that involve some sort of impact on the body-such as running or jumping-are best for building bone.
"The bone is going to adapt to the strains placed upon it. Jumping up and down from a box 50 times a day is probably perfect in that respect," she says.

She warns that for some people, especially those with osteoporosis, exercise that involves significant strain or heavy impacts can be detrimental, possibly triggering fractures. Such individuals should
always seek a physician's advice before beginning a training program.

The immune system also benefits from an active lifestyle. The 1996 Surgeon General's report, "Physical Activity and Health," states that "moderate exercise has been shown to bolster the function of certain components of the human immune system-such as natural killer cells, circulating T-and B-lymphocytes, and cells of the monocyte-macrophage system-thereby possibly decreasing the incidence of some infections and perhaps of certain types of cancer."

It cautions that over-training, or prolonged high-intensity exercise could have an adverse effect on the immune system, possibly reducing the ability of immune cells to attack microbes that gain entry to the body. Davies says that while starting good exercise habits early in life is important, it is never too late to begin.

"Older people enjoy the same increases in muscle tone and cardiovascular health and everything else," even though there is a slight, and very slow decrease in a person's maximum performance level with age, he says. "A person who runs 100 meters in nine seconds at 20 years old will not be able to do so at age 60, so there is a clear decrement in maximum performance over time. But in general that decrease is fairly minor," he says.

"Many people lose muscle mass and muscle tone as they age, but only a small fraction of that loss is actually due to aging. For the most part, what you're seeing is really caused by a lack of exercise."
Still, he adds that "the good news is that no matter what your age, you can regain a lot of what you've lost." The trick is to do activities that you enjoy, and that do not cause any physical pain or harm. For example, someone with knee problems should avoid exercises that exacerbate them, such as running.

"You don't want to do an activity that improves your cardiovascular system but destroys your knees, because if you're healthy for five years and an invalid for the rest of your life, that's a bad trade-off," he says. Davies adds that those over age 50 who have not been exercising should consult a doctor before beginning an exercise regimen.

According to the Surgeon General's report the best exercise recommendations based on current research are that:

• All people over the age of 2 should accumulate at least 30 minutes of endurance-type physical activity, of at least moderate intensity, on most-preferably all-days of the week.
  
• Additional health benefits can be achieved by adding more time in moderate intensity activity, or by substituting morevigorous activity.
• Persons with symptomatic cardiovascular disease, diabetes, or other chronic health problems who would like to increase their physical activity should be evaluated by a physician and provided with an exercise program appropriate for their clinical status.
• Previously inactive men over age 40, womenover age 50, and people at high risk for cardiovascular disease should first consult a physician before embarking on a program of vigorous physical activity to which they are unaccustomed.
  

Not surprisingly, the conclusions reached in the Surgeon General's report directly echo that of Hippopcrates, who said more than 2,300 years ago: "If we could give every individual the right amount of...exercise, not too little and not too much, we would have found the safest way to health."

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