Curious Folks Ask Part 9

In one study, a congenitally blind woman described a dream about sitting at a table in a nice restaurant. She knew she was at a table through kinesthetic sense-the sense mediated by feedback from organs in the muscles and tendons. She knew it was a nice restaurant because she felt the thick carpet and heard the quiet atmosphere. She had an image of the table because she had previously felt tables. Similarly, a congenitally blind woman in another study described being in a room with a device that looked like an ATM. She said she knew what it looked like from prior experience touching the b.u.t.tons on an ATM.

Studies that have compared the composition, organization, and themes of the dreams of blind people and sighted people have found few differences. Blind people reported more dreams in which they had a misfortune occur during locomotion or transportation, and dreams about their guide dogs, consistent with the notion that there is continuity between dream content and waking experiences.

Hullabaloo We are all aware of the increase in violence in our society. Is the increasing amount of electronic noise in the atmosphere possibly interfering with brain waves?

About two decades ago, descriptions of a new illness started showing up in the medical literature. It was actually a diverse collection of symptoms: skin problems, dizziness, headaches, fatigue, muscle pain, nausea, problems with concentration and memory, depression, and nervousness.

More people became convinced that their symptoms were being caused by "electromagnetic pollution." They believed that they were affected, while others working under the same conditions were not, because they were particularly susceptible to environmental electromagnetic fields. Hence, the mysterious illness was dubbed "electromagnetic sensitivity syndrome."

Electromagnetic fields are nothing new. Light is a form of electromagnetic radiation, as are the radio waves that bring us our favorite tunes and talk shows and the microwaves that heat up our frozen dinners. However, advancing technologies and rising demand for electricity have steadily increased our exposure to electromagnetic fields.

In response to concerns about the possible health effects of exposure to electromagnetic fields, the World Health Organization (WHO) launched the International EMF Project in 1996 to review studies on the health effects of exposure to these fields.

One concern is the possibility that low-frequency electromagnetic fields could generate currents within the human body. After all, our heartbeat, communication between nerve cells, and the chemical processes that keep our cells alive involve the movement of charged particles. While large electromagnetic fields could stimulate nerves or affect other biological processes, the WHO concludes that the fields we encounter are too small to produce these effects.

An additional concern is that exposure to radiofrequency fields, especially from cell phones, could cause heating of the brain. Even a small amount of heating by radiofrequency fields has been shown to affect brain activity and behavior in animals. However, the majority of scientists consider the fields produced by cell phones too small to heat the brain.

In laboratory studies it has also been difficult to show that the symptoms of electromagnetic sensitivity syndrome have anything to do with exposure to electromagnetic fields. Therefore, our exposure to these fields does not seem to have any significant effects on health or behavior, including violence, but research is ongoing. The WHO acknowledges that if long-term exposure to these fields negatively impacts a small number of people but is harmless to everyone else, the effects would be tricky to detect.

Sentiment sites What are emotions? Do they reside in specific parts of our brain, or are they the result of our cognitive thinking? Are emotions genetic, or are they learned? Do animals have emotions?

A fully accepted theory of emotion is lacking, but research has provided tantalizing insights. Our experience tells us that emotions have bodily manifestations such as changes in heart rate, irregular breathing, increased or decreased blood flow to the skin or digestive tract, sweating, and trembling. However, it is not quite as simple as saying that because individuals have a certain set of physiological responses, they experience a particular emotion. Cognition also plays an important role.

When provided with an alternative explanation for their physiological responses, people appear to rationalize what they are feeling, rather than automatically experiencing it as an emotion. In one study, people were given an injection of salt.w.a.ter and either were told that a side effect of the "vitamin shot" was trembling and a pounding heart or were not told anything. The individuals who had been told about the side effect reported experiencing less intense emotions when placed in an anger-provoking or amusing situation.

Several brain regions play a role in our experience of emotions. The hypothalamus controls the autonomic nervous system, which regulates our physiological responses. The amygdala draws our attention to dangers in the environment that might require an emotional response. The hippocampus is involved in learning and memory, including emotional memories. The cortex helps us choose the most appropriate response in an emotional situation.

Babies can express emotions from a very young age, and expressions of emotion are remarkably cross-cultural. In the late 1960s, researchers discovered that members of a tribe in a remote area of Papua New Guinea, who had never been exposed to Western culture, could accurately interpret facial expressions in photographs of Westerners. And Westerners accurately interpreted the expressions of tribe members. Not all aspects of emotional expression are inborn; cultural rules define when such expressions are appropriate. Which situations evoke emotions is also partly learned.

In 1872, Charles Darwin published The Expression of Emotion in Man and Animals The Expression of Emotion in Man and Animals, in which he suggested that human expressions of emotion evolved from similar expressions in other animals. One recent study found that chimpanzees shown videos of emotional scenes (a veterinarian pursuing chimps, a chimp getting a treat) could correctly choose a photograph of another chimp expressing the emotion that the scene would evoke. Of course, although other animals produce and interpret what appear to be expressions of emotion, we cannot determine if their subjective experience of emotion is the same as ours.

Feeling groovy I have read that the cause of pleasure is dopamine in the brain. I have also read that serotonin is the feel-good chemical, and runner's high is said to be due to endorphins in the brain. Which is the main cause of pleasure, or do they all interact?

The neurotransmitters dopamine, serotonin, and endorphins are three of several chemical languages known to play a role in feelings of pleasure and well-being. Nerve cells chatter in more than 100 different dialects, and future research will likely implicate more of these in our brains' pleasure conversations.

The discovery of reward circuitry in the brain dates to the 1950s, when researchers made a surprising discovery while investigating the effects of electrical brain stimulation on rats' ability to learn. When electrodes are implanted in a certain region of the brain, rats will press a lever to the point of exhaustion to self-administer electrical stimulation. People given electrical stimulation in the a.n.a.logous brain region say the experience is intensely pleasurable.

At the core of this reward circuit are nerve cells that originate near the base of the brain, in the ventral tegmental area. They send projections toward the nucleus acc.u.mbens, a structure deep beneath the front of the brain. Dopamine is the main neurotransmitter at these connections. Nerve cells using a variety of neurotransmitters connect the reward circuit with brain regions involved in memory and emotion, which influence the reward response.

This system ensures that an organism eats, drinks, and engages in other adaptive behaviors. Addictive drugs hijack it. For example, heroin makes nerve cells churn out more dopamine. Cocaine inhibits the reuptake of dopamine by the nerve cells that release it, preventing dopamine chatter from being quickly silenced.

In depression, a preeminent factor is the reduced activity of nerve cells that communicate using serotonin. Selective serotonin reuptake inhibitors (SSRIs) are the medication of choice for many depressed people.

Unfortunately, the rate of remission with SSRIs is less than 50 percent, and multiple neurotransmitter systems and multiple brain regions have been implicated in depression. Among them are dopamine and the brain's reward circuitry, consistent with one of the many symptoms of depression, anhedonia-the inability to experience pleasure.

Avid runners talk about the euphoric state they get from long-distance running. Often they cannot abstain from running, even when they are injured. The addictive aspect of running appears to be due to the brain's natural opium-endorphins-which, during strenuous exercise, is released into a region of the brain that controls mood.

Mad genius It seems that many famous artists and writers have suffered from bouts of madness. Is there a relationship between creativity and mental illness, or does it just seem that way because odd or tragic characters are more likely to be remembered?

The idea that madness and creativity are linked goes back to antiquity, but it is not without controversy. Some schools of psychological thought consider creativity to be linked with sound mental health. Today, the prevailing view is that creative genius and some mental disorders are linked, but not necessarily directly.

Three sources of evidence have been mined to determine the relationship between mental disorders and creativity. First, historical data, especially biographies of renowned creators, have been a.n.a.lyzed for indications of symptoms a.s.sociated with various psychopathologies. Second, psychiatric research has examined the incidence of diagnosed mental disorders and treatment in samples of contemporary creators. Third, psychometric studies-standard personality questionnaires-have compared creative and noncreative individuals.

Conclusions from the three types of studies are consistent. People who are highly creative are more likely to have certain mental disorders, especially depression, than otherwise comparable, less creative individuals. The prevalence and intensity of the symptoms varies among different domains of creativity. For people working in the creative arts, the lifetime prevalence of depression is 50 percent, compared to between 20 and 30 percent for people in business, scientists, and important social figures. Within the creative arts, writers of poetry and fiction and visual artists are most likely to suffer from depression.

Because the defining symptoms of depression include lack of interest and energy and difficulty concentrating, it is paradoxical that depression is a.s.sociated with creative behavior. Indeed, depression does not appear to be the cause of creative productivity. During a depressive episode, creativity is not enhanced, and mood stabilizers have been found to increase, rather than diminish, productivity.

Instead, studies suggest that a personality trait, self-reflective rumination-conscious, recurring thoughts focused on one's inner feelings-may be the explanation for the paradox. The tendency to ruminate has been shown to increase vulnerability to depression. Rumination has also been shown to enhance creative ability and interest. In other words, depression and creativity happen to be linked because a third factor causes both.

The role of rumination could also explain the lower prevalence of depression among scientific creators versus artistic creators. Original thinking is important in the arts and sciences. In contrast, introspection is less useful for providing ideas that could advance science than it is for providing original content for poetry and other artistic endeavors.

Out of body I have had three out-of-body experiences. Is there a relationship between the alternate-universe theory and out-of-body, or are they independent of each other?

Despite their New Age mystique and a.s.sociation with certain substances consumed by hippies, out-of-body experiences are reported by many people, particularly those who suffer from migraines and neurological conditions. Studies of out-of-body experiences have recently been published in highly respected journals, including Science Science and and Nature Nature.

These studies do not tie the phenomenon to alternate universes, though. The existence of multiple, parallel universes is predicted by the complicated mathematics of quantum physics. Even if these alternate universes exist, physicists say it is impossible to access or even perceive them.

Instead, the study of out-of-body experiences is the purview of psychologists and neuroscientists. Out-of-body experiences have been accidentally induced in patients undergoing focused electrical stimulation of the brain during epilepsy treatment. For example, one patient described an instantaneous feeling of lightness and the sensation that she was floating above the bed during the electrical stimulation of a region of her brain called the angular gyrus.

The angular gyrus is on the surface of the brain, toward the rear, and it is a region that receives input about vision, hearing, and touch. The angular gyrus is also close to the vestibular cortex, which processes sensory information to maintain the sense of balance. The brain stimulation research suggests that out-of-body experiences may be caused by the dissociation of information coming simultaneously from two or more senses.

This hypothesis is supported by recent studies that used head-mounted video displays to give people visual information that placed them in a different location. The visual information on its own did not give people the feeling of being outside their bodies. But when they saw their virtual body being touched at the same time as their real body was being touched, they felt as if the virtual body was their own body. Then, when a hammer was swung so that it appeared to hit the virtual body, measurements of skin conductance-a measurement of stress-indicated that the hammer was registered as a threat, even though it posed no real danger.

The studies show that information from the senses can modify the brain's representation of the physical body. In addition to shedding light on out-of body experiences, the research provides insight into consciousness, since the feeling of being within one's physical body is a foundation of the concept of self.

Musical mind Your out-of-body experience answer must have been rea.s.suring to anyone who's had the experience and was disbelieved when they described the event. I'm writing about a different kind of "out-of-body" experience-music playing in one's head. In addition to a variety of music, I also hear noisy motors, a distant train, or nonmusical drumming. Have you come across any information on this kind of auditory hallucination?

Everyone has had an earworm-a snippet of a song playing repeatedly in their head like a broken record. Someone's ringtone, a visit to Disneyland, or even the mere mention of an annoying tune (I promise I'll refrain) is enough to set it off. What distinguishes a musical hallucination from an earworm is that a musical hallucination appears to originate from outside your head.

People are often afraid to admit that they are hearing things for fear they will be thought of as mentally ill. But auditory hallucinations seem to be fairly common in mentally sound people who have ear problems. In one study, researchers interviewed 32 people who had lost hearing in both ears and discovered that all had experienced musical hallucinations.

These hallucinations are a form of tinnitus-usually a more generic buzzing or ringing in the ears. Changes in fluid levels in the inner ear (with or without hearing loss), as occur in Meniere's disease, can cause auditory hallucinations in some people, as can many drugs, including alcohol, blood pressure medication, and even aspirin.

Musical hallucinations are considered to be a.n.a.logous to Charles Bonnet syndrome, in which visually impaired people see things that are not there, and phantom limb syndrome, in which amputees have sensations that seem to be in their missing limb. The common link among these syndromes is sensory deprivation. According to one explanation (Release Theory), normal sensory input suppresses the nerve circuits in which sensory memories are stored. When these circuits are no longer inhibited, previously recorded perceptions are "released" and re-experienced.

Depending on the cause, musical hallucinations can be reduced with a hearing aid (if hearing loss is involved), controlling the body's retention of fluids (if changes in fluid volume in the inner ear are involved), or changing medications in consultation with a physician. One case report described a woman who could "think" down the volume of her musical hallucinations.

Perhaps it is even possible to harness the hallucinations for good. Some researchers believe that musicians are predisposed to musical hallucinations. Famous composers, including Beethoven and Schumann, experienced them.

8. Health nuts

Counting calories

How do nutritionists determine the caloric content of a complex dish when it is impossible or impractical to total up the individual ingredients?

One way is to measure the amount of thermal energy produced when the food is completely combusted into carbon dioxide and water in a device called a bomb calorimeter. To avoid overestimating the actual calories available from food, bomb calorimetry measurements of fecal matter must be subtracted from those of the food.

This method is sometimes used for animal feed, but it is not very popular because bomb calorimeters are pricy. Plus, it is kind of a drag for researchers to have to follow people around with baggies to determine the caloric content of what pa.s.ses through our digestive systems unscathed.

Instead, total energy content is usually determined by adding up the energy contributions of fat, proteins, and carbohydrates in food. Fat can be extracted from the food with chemical solvents and then quantified. Protein contains 16 percent nitrogen on average, so the amount of protein is calculated from food's total nitrogen content. The amount of carbohydrate is usually calculated from the total ma.s.s of the food minus the amount of fat, protein, moisture, and minerals.

Back in the late 19th century, W. O. At.w.a.ter and other researchers at the U.S. Department of Agriculture did the dirty work to determine the average amount of energy yielded from fat, protein, and carbohydrates after accounting for losses in digestion. The conversion factors are 9 calories (referred to as kilocalories outside the United States) per gram of fat, 4 calories per gram of protein, and 4 calories per gram of carbohydrate.

The 9-4-4 conversion factors can be misleading because different fats, proteins, and carbohydrates have different structures and digestibilities. For example, multiplying the total grams of carbohydrate by 4 overestimates the amount of energy the body can extract from high-fiber foods. For this reason, the ma.s.s of insoluble fiber usually is subtracted from the total carbohydrate before the energy calculation is made.

If the exact ingredients are known, it is possible to use the At.w.a.ter specific factor system, which is a series of tables listing the number of calories in the fats, carbohydrates, and proteins in specific foods. For example, the tables reveal that the protein in eggs provides nearly 1 more calorie per gram than the protein in soybeans. On average, the specific factor system yields energy values that are about 5 percent lower than those obtained using the general conversion factors.

Fat carbs, skinny carbs What's the big deal about carbohydrates? Why should we be on a low-carb diet? (Or should we?) You are right to be skeptical. We are at one end of a pendulum swing. Remember not so long ago, when fat was the bad guy and "low-fat" or "no-fat" labels sold food?

Throughout much of the low-fat era, we acted as if as long as we ate foods that were low in fat, we could eat whatever we wanted, even if the foods were high in calories or sugar. The problem is simple: if you take in more calories than you burn, regardless of whether those calories are from fat or carbohydrates, you gain weight.

Cutting carbohydrates results in weight loss only if total calorie intake is reduced, not if the calories from carbohydrates are simply replaced by calories from fat or protein.

Toward the end of the low-fat era, but before the low-carb craze, we started to develop a more nuanced view of fat, accepting, for example, that fish oils can help reduce heart disease. Now we also need to develop a less black-and-white view of carbohydrates.

Not all carbs are created equal. Many of the carbohydrates in the typical American diet come from highly refined grains. To make them easier to use in cooking, grains are milled to remove their outer coating, leaving the starchy portion of the grain. Unfortunately, the outer portion of the grain is high in fiber, B vitamins, and trace minerals such as copper and zinc.

In addition, foods made from refined grains, like white bread, are digested quickly into glucose, causing blood sugar to spike rapidly. Foods that cause rapid increases in blood sugar are said to have a high glycemic index, and diets that are filled with such foods have been linked to heart disease and diabetes.

On the other hand, carbohydrates like brown bread, brown rice, and whole grain pasta have a low glycemic index. Not only do they not cause spikes in blood sugar, but they also are rich in vitamins, minerals, and fiber, which can protect against cancer and decrease cholesterol.

Most Americans do not get enough servings of whole gains every day. You can find out more about carbohydrates and the glycemic index at the Harvard School of Public Health website: http://www.hsph.harvard.edu/nutritionsource/carbohydrates.html.

Perhaps in terms of diet we could learn from the French, who are inclined to define healthy eating more in terms of balance, variety, and freshness. Healthy eating is not about demonizing certain foods. Studies repeatedly show that Americans are not getting enough of the foods that are good for us, especially fruits, vegetables, and whole grains. Hopefully, when the pendulum swings again, "balance" will be the mot du jour mot du jour.

Combo meal For breakfast, I usually have orange juice, an egg, toast, and coffee. If I ate these items separately over a period of, say, two to three hours, would I get more nutritional benefit from this combination of food, rather than by eating them all in one sitting?

Despite our natural aversion to pairing certain foods (pickle cookies, anyone?) and the popularity of "dissociated diets," there is limited scientific data on the value of eating foods separately versus in combination.

It is well known that vitamins and minerals can interact synergistically or antagonistically, but most of these interactions are determined by the composition of the overall diet. For example, a magnesium deficiency can interfere with the body's metabolism of sodium, pota.s.sium, calcium, and phosphorus.

Within a single meal, some nutrient interactions occur. One study showed that when calcium was added to a meal, it significantly reduced iron absorption. So calcium fortification of orange juice or milk in your coffee could reduce the amount of iron your body can extract from your toast and egg. On the other hand, the vitamin C in orange juice facilitates iron absorption. In any case, the body seems to adjust over time, because another study showed that iron levels in the blood were unaffected by taking calcium supplements with two meals daily for a few months.

Proponents of dissociated diets would tell you to eat your egg separately from your toast and juice, and not to add b.u.t.ter or whole milk to your breakfast mix, because intake of carbohydrates, fats, and proteins should be spread throughout the day. One of their arguments is that if carbohydrates, which effectively simulate the release of insulin, are ingested with fats, insulin will cause more fat to be stored.

This argument was debunked in a comparison of two low-calorie diets-one that combined fats and carbohydrates within meals, and another that separated fats and carbohydrates into different meals. Weight loss was the same in the group on the dissociated diet as it was for the group on the mixed diet. Both diets decreased blood glucose, insulin, cholesterol, and blood pressure by a similar amount.

Some people recommend minimizing the intake of liquids with food to avoid diluting the digestive enzymes, but if your goal is to rehydrate, this rule doesn't hold water. Liquids are better retained when they are consumed with meals.

Of course, individual foods are a combination of many nutrients. For instance, an egg is approximately equal parts protein and fat, with a tad of carbohydrate and a long list of vitamins and minerals. So our digestive systems come equipped to tackle those pickle cookies-if only our palates were up to it.

Chug-a-lug I try to drink eight gla.s.ses of water a day, but instead of drinking one gla.s.s every hour or so, I drink three 8-ounce gla.s.ses when I wake up in the morning, another three at lunch, and two in the afternoon. Am I getting the necessary hydration that my body needs?

Aliens studying earthlings over the past couple decades would almost certainly have noted a strange phenomenon: we have become as attached to our water bottles as Charlie Brown's friend Linus is attached to his blanket. (I confess: A large water bottle is within reach as I write this.) "'Drink at least eight gla.s.ses of water a day.' Really? Is there scientific evidence for '8x8'?" may seem like a surprising t.i.tle for a journal article (published in the American Journal of Physiology American Journal of Physiology in 2002) considering the ubiquitous nature of this health recommendation. Perhaps even more surprising is the conclusion of its author, Heinz Valtin, a physician and kidney specialist at Dartmouth Medical School. in 2002) considering the ubiquitous nature of this health recommendation. Perhaps even more surprising is the conclusion of its author, Heinz Valtin, a physician and kidney specialist at Dartmouth Medical School.

Although Valtin found some evidence that individuals with very low fluid intake are at greater risk for bladder cancer, colorectal cancer, heart disease, and migraines, the research studies failed to definitively prove the connection. Overall, he concluded that the wide range of claims about the health benefits of drinking eight gla.s.ses of water a day is largely unsupported. He also argued that although hot weather and physical activity increase water needs, eight gla.s.ses is more than sedentary individuals in a temperate climate typically need.

In terms of getting the maximum hydration from the water consumed, a study found that a few gla.s.ses of water ingested over a couple of hours are largely retained, while the same amount of water ingested in 15 minutes is not. Individual variation is large and depends on daily salt intake. The sodium ion concentration in the blood influences a brain sensor called an osmostat, which sends signals that control thirst and water retention.

Water ingested with food is better retained, and contrary to popular belief, it does not slow digestion. Rats allowed to drink during a meal digested their food at the same rate as rats deprived of water during the meal.

Water intake can influence calorie intake. On a 12-week diet, middle-aged and older adults who drank two gla.s.ses of water a half hour before meals ate less and lost 5 pounds more than those who did not drink water before meals. Water does not seem to curb appet.i.te in younger adults, but in another study, increasing the water content of the foods themselves decreased calorie intake.

Cocoa craze Is chocolate good for you? Does it matter what kind of chocolate you eat?

Chocolate has been touted as "the new red wine" for its putative health benefits. The excitement centers on a cla.s.s of compounds called flavonoids, which are antioxidants. Raw cocoa is one of the richest known sources of flavonoids, with more than 10 percent flavonoids by weight.

Studies indicate that isolated flavonoids, or chocolate that contains flavonoids, may have favorable effects on five risk factors a.s.sociated with heart disease. First, flavonoids scavenge free radicals, thereby inhibiting the oxidation of low-density lipoprotein (LDL). This process is beneficial because the oxidation of LDL promotes the formation of plaques-deposits-in the arteries. Second, flavonoids inhibit another early event in plaque formation-the adherence of white blood cells to the lining of the arteries.

Third, they increase high-density lipoprotein (HDL), which helps remove cholesterol from the body. Fourth, like aspirin, flavonoids reduce the reactivity of platelets-the smallest structural units in the blood. As a result, platelets become less likely to stick together to form a blood clot. Fifth, flavonoids increase nitric oxide levels, which dilates the blood vessels and reduces blood pressure.

Some evidence suggests that flavonoids protect against cancer and possibly neurodegenerative diseases. They have also been shown to decrease insulin resistance.

However, all the support for the health benefits of flavonoids comes from epidemiological studies and very short-term experimental studies. Although epidemiological studies address the long-term consumption of flavonoids, such studies are problematic because they compare naturally occurring populations, which may differ in more than just their cocoa consumption habits. So far, no long-term experimental studies have addressed the health benefits of chocolate consumption, nor have different types of chocolate been systematically compared.

Not all chocolate is created equal. The concentration of flavonoids depends on the variety of cocoa plant and the growing conditions. By far the most important factor in flavonoid concentration is how the beans were processed. Most chocolate products on the market today contain little or no flavonoids because flavonoids are destroyed by fermentation, roasting, and treatment with alkali. Experimental studies of chocolate consumption often use non-commercially available high-flavonoid chocolate.

If otherwise processed the same way, dark chocolate contains more flavonoids than milk chocolate. In the United States, the Food and Drug Administration mandates that dark chocolate contain at least 15 percent chocolate liquor from ground or melted cocoa nibs. Milk chocolate must contain at least 10 percent. White chocolate does not contain any cocoa solids and therefore is devoid of flavonoids.

Go the distance There has been speculation that women will do better than men in ultra marathons of 50 miles, 100 miles, or more, because male marathon runners "hit the wall" after about 20 miles, when they've used almost all their glycogen and start burning mostly fat. Women don't have this problem, because they are better at burning fat. Is there much evidence that women are doing better than men in ultra marathons?

Until 1972, women were officially barred from running marathons in the United States, and not until 1984 were they permitted to run the Olympic marathon. Once women were allowed to compete in the 26.2-mile race, their times improved so rapidly that a 1992 article in the journal Nature Nature predicted that women would catch up to men by 1998. That did not happen, but now less than 12 minutes separate the fastest female and male marathoners. predicted that women would catch up to men by 1998. That did not happen, but now less than 12 minutes separate the fastest female and male marathoners.

In the ultra (anything longer than a marathon), women have already caught up to men-at least in one race. In 2002 and 2003 a female runner won one of the world's most grueling races, the Badwater Ultramarathon. The race begins in the Badwater Basin in Death Valley, California, and continues 135 miles to the base of Mount Whitney, with more than 8,500 feet of elevation gain, in brutal summer heat. Women are often in the top five finishers of Badwater.

Many hypotheses have been proposed to explain why women may have an advantage over men in long-distance running. Psychological factors, such as better resistance to pain or better ability to pace oneself, could play a role. Size may matter; lighter runners are better able to maintain a balance between production and dissipation of thermal energy. Some studies, but not all, have found that women burn fat better than men do during prolonged exercise.

After years of dramatic improvements, female distance runners now seem to be improving at the same rate, rather than faster than men. Also, men and women who ran equally fast at near-marathon distance performed similarly in 50-mile and 100-mile races, in the largest comparison to date. So the idea that women have an advantage over men at long distances is still controversial.

Marathons, even ultras, have become a social and fitness phenomenon. More than 400,000 marathon finishing times were recorded in the United States last year, and women are now 40 percent of marathon finishers. Considering how recently women's distance running gained societal acceptance, I think we ain't seen nothin' yet!

Exercise regimen I try to run four miles a day on my treadmill, but I don't have the stamina to do it all at one time. Therefore, I run one mile, and later I run another mile, and so on. Is there a drawback to the benefits I receive by breaking it up this way (such as calories burned)?

Many studies have compared the benefits of continuous versus split exercise sessions because any differences have implications for public health recommendations. This research suggests that the health benefits of split exercise sessions compare favorably with those of continuous exercise sessions.

Regardless of the structure of the workout, the number of calories burned is elevated both during and after exercise. This means that the same old couch potato routine burns more calories after a workout. How long your metabolism remains cranked up after exercise depends on the workout's duration and intensity. The increase in metabolism following exercise is due to the many processes involved in repairing and getting fuel back into the muscles, and removing lactic acid and other cellular waste products.

Splitting the same workout into multiple sessions does not alter how many calories are burned during the total workout, as long as the total work performed remains the same. But some studies show that the post-exercise calorie burn is greater when the workout session is split. The difference is small-it would amount to about one slice of apple pie guilt-free after a month of daily split workouts instead of continuous workouts. Varying the intensity during a continuous workout, while maintaining the same average intensity, has been shown to have the same effect as splitting the workout.

Split and continuous workouts also seem to have an equally favorable effect on blood pressure, other measures of cardiorespiratory fitness, and cholesterol levels. The only caveat is that nearly all the studies comparing continuous and split workouts have been short-term. Therefore, it is possible that undiscovered long-term differences exist in how different workout schedules affect the risk of heart disease, diabetes, and cancer.