That’s because science progresses in fits and starts. Researchers put forward a possible explanation, a hypothesis, for the results of an experiment. Other researchers attempt to duplicate their results and refine the hypothesis. Sometimes the hypothesis is completely discarded, and a new hypothesis gains sway.

But in the media, this slow process is seldom reported. It’s much easier to pick up on the report of a single study—particularly if it has startling results—and present the hypotheses put forward by its authors as fact, rather than simply one possible interpretation.

I’m sure I’ve been guilty of that myself in this column, though I try to avoid it by using phrases which, if I could only charge a dollar to every reader for each use, would have long since made me rich: “One possible explanation…” “The researchers suggest…” and, of course, “More research is needed.”

By this time you’ve probably twigged to the fact that I’m about to tell you that something you may think is a fact is anything but—and you’re right.

Go to any gym, and you’re likely to see people engaging in the time-honored practice of static stretching, bending themselves into a pose that pulls muscles and tendons tight and holding it for a few seconds.

They do this because they’ve been told, at some point, that it’s important to “stretch out” before engaging in vigorous physical activity, in order to avoid injury.

Guess what?  In all likelihood, they’re wasting their time.

This isn’t exactly news, or shouldn’t be. As Cynthia Billhartz Gregorian points out in a story in the St. Louis Post-Dispatch, it’s been five years since the Centers for Disease Control and Prevention reviewed 361 research studies done by its epidemiology program office and found no evidence that stretching either before or after exercise prevents either injury or muscle soreness.

In fact, some sports medicine experts say static stretching actually inhibits performance, decreasing power and speed, and can cause micro-tears in tendons, ligaments and muscles. Nor is stretching going to help you work out a strain: stretching it makes it worse, not better. Strained muscles should be rested, and then the focus should be on rebuilding strength.

So should you give up stretching altogether? (You know, just like you gave up coffee and chocolate before you found out both are good for you?)

No; but you might want to think twice about static stretching. Modern thinking—you know, as opposed to that old pre-2004 thinking—holds that dynamic stretching is the way to go: moving through stretches without pausing or holding a position, walking forward while grabbing the knee toward the chest, that kind of thing. A little jogging in place or skipping while swinging your arms, or going through the required motions of a particular sport at half-speed might help.

Now, static stretching does have some benefits. If you do it every day for three months, it will make you more flexible, for instance. “Senior athletes” can benefit by doing traditional stretching after—but not before!–their main workout, because it helps minimize the effects of arthritis and joint degeneration. And any athlete can benefit from static stretching after prolonged exercise because it reduces lactic acid accumulation in heavily exercised muscles.

But beforehand? Not recommended.

When you think about it, our physically active ancestors didn’t worry about stretching. As California doctor-and-author Dr. William Meller points out, “Can you imagine a caveman engaging in a program of stretching before heading out to chase down prey?” And I doubt most farm hands carefully stretched before going out for a day of tossing hay bales onto a wagon.

So why have we been stretching all these years? Because at some point, researchers decided it was good for us. Scientists continued to study the issue, however, and our knowledge evolved.

Which gives me great hope, because personally, I’m hoping for a study that says the whole “exercise is good for you” thing is similarly misguided.

If I find one, you’ll hear it here first!

The first bicycle was the “celerifere,” or wooden horse, invented in France in the 1790s. It had a fixed front wheel, so it couldn’t be steered, and the rider propelled it by pushing his feet along the ground, like Fred Flintstone.

A German baron, Karl von Drais, added a steerable front wheel in 1817, creating the “draisienne,” or dandy horse. In 1839, Kirkpatrick Macmillan, a Scottish blacksmith, added pedals which drove the rear wheel by means of cranks.

In the 1860s the French invented the velocipede, on which the pedals were attached directly to the front wheel, so that once around with the pedals meant once around with the wheel. That meant that the larger the front wheel, the faster the bicycle. This led to the “pennyfarthing” bicycle, on which the front wheel might be 1.5 metres tall or more, and the back wheel only a quarter as big. They look incredibly dangerous and unstable to us…and they were.

The growing numbers of bicycle accidents led Englishman H. J. Lawson to invent the “safety bicycle,” which had a chain and sprocket driving the rear wheel, in 1879. Six years later fellow Englishman J. K. Stanley created a safety bicycle with wheels of equal size. After that, improvements came fast and furious: pneumatic tires in the 1880s, two and three-speed hub gears in the 1890s, and derailleur gears in 1899, the last major technological advance until the 1970s.

A bicycle takes the pumping action of your legs, driven by the energy you derive from food and oxygen, and uses it to spin a wheel. Friction between the rear tire and the surface of the road drives the bicycle forward.

Road bikes and touring bikes generally have thinner tires than mountain bikes. The thin road tires are inflated to 100 or even 120 PSI, so they don’t flatten out much. That means less surface area contacts the road, which means less friction and more speed.

Wide mountain bike tires flatten out more on a hard asphalt surface, making it harder to pedal the bike, but on a dirt trail, the fatter, softer tires float on top of the rough surface. A thin, hard road tire would cut deep into the dirt.

Once you’re rolling on any kind of surface, it becomes easier to balance on the bicycle. Scientists aren’t sure why. One theory, which makes intuitive sense, is that it’s because a spinning wheel has “angular momentum”: it likes to keep spinning at whatever angle it started spinning at, and resists being tipped. This resistance helps keep the bicycle upright.

Recently, British scientist David Jones set out to create an unrideable bicycle. He built a bike in which the gyroscopic action of the front wheel was cancelled out by a wheel mounted next to it that rotated in the opposite direction–and found that it didn’t affect either the stability or steerability of the bicycle. Which may mean the spinning wheels don’t have anything to do with stability at all, and scientists will have to look elsewhere for an explanation.

Like any other moving object, a bicycle tends to keep moving in a straight line until acted upon by some other force. Bicycle brakes are usually a set of rubber calipers that grip the hub of the wheel. The friction between the calipers and the hub drains energy out of the spinning wheel, turning it into heat.

The bicycle’s rear wheel is spun by a gear attached by a chain to another gear attached to the pedals. If the chain is on a big gear in front and a small gear in back, you’ll find it hard to pedal but you’ll go really fast, because every time the front gear goes around, the little rear gear goes around more than once, taking the rear tire with it. Vice versa, use a small gear in front and a large one in back, and you’ll find it very easy to pedal but very slow going, because now the rear wheel is spinning fewer times per pedal revolution — maybe not even once. This is useful for going up hills and against the wind.

The importance of these lower gears cannot be overstated, for there is one preeminent principle governing bicycles, known simply as the First Law of Bicycling:

No matter which direction you ride, it’s always uphill and against the wind.

The first step in the development of the bicycle was the “celerifere,” or wooden horse, invented in France in the 1790s. It had a fixed front wheel, so it couldn’t be steered, and the rider propelled it by pushing his feet along the ground, a la The Flintstones.

A smart German baron, Karl von Drais, finally realized the machine would be a lot more fun if you could steer it, and added a steerable front wheel in 1817, creating the “draisienne,” or dandy horse. In 1839, Kirkpatrick Macmillan, a Scottish blacksmith, made a machine with pedals, which drove the rear wheel by means of cranks.

In the 1860s the French took the initiative again, inventing the velocipede, on which the pedals were attached directly to the front wheel, so that once around with the pedals meant once around with the wheel. That, in turn, meant that the larger the front wheel, the faster the bicycle. This led to the “pennyfarthing” bicycle, on which the front wheel, over which the rider sat, might be 1.5 metres tall or more, and the back wheel only a quarter as big. They look incredibly dangerous and unstable to us, and while looks can be deceiving, in this case they aren’t, especially considering the poor roads of the time.

The growing numbers of bicycle accidents led Englishman H. J. Lawson to invent the “safety bicycle,” which had a chain and sprocket driving the rear wheel, in 1879. Six years later fellow Englishman J. K. Stanley created a safety bicycle with wheels of equal size. After that, improvements came fast and furious: pneumatic tires in the 1880s, two and three-speed hub gears in the 1890s, and, just in time to kick off a brave new century of cycling, derailleur gears in 1899, the last major technological advance until the 1970s.

Bicycles are the most energy-efficient form of transportation, because they’re lightweight and barely make contact with the ground, which minimizes friction. (Energy efficiency isn’t necessarily a selling point, though, when the energy being used is yours — at least, that’s the way I feel some mornings facing the ride to work!)

A bicycle takes the pumping action of your legs, driven by the energy you derive from food and oxygen, and uses it to spin a wheel. Friction between the rear tire and the surface of the road drives the wheel forward, taking the bicycle — and you! — along.

Once you’re rolling, it becomes easier to balance on the bicycle. That’s because a spinning wheel has “angular momentum”: it likes to keep spinning at whatever angle it started spinning at, and resists being tipped. This resistance helps keep the bicycle upright. (Of course, tip it far enough, and gravity overwhelms angular momentum!) In effect, every bicycle has its own pair of stabilizing gyroscopes.

A bicycle also has the usual kind of momentum, the tendency of an object to keep moving in a straight line until acted upon by some other force. Unless you enjoy stopping by running into parked cars (an effective but drastic way to discover your own personal momentum, separate from that of the bike), you need brakes. Bicycle brakes are usually a set of rubber calipers that grip the hub of the wheel. The friction between the calipers and the hub drains energy out of the spinning wheel, turning it into heat.

The wheel is spun by a gear attached by a chain to another gear attached to the pedals. The ratio between the front and rear gears determines how quickly the rear wheel spins in response to one revolution of the pedals. If the chain is on a big gear in front and a small gear in back, you’ll find it hard to pedal but you’ll go really fast, because every time the front gear goes around, the little rear gear goes around more than once, taking the rear tire with it. It’s hard to pedal because it takes a lot of energy to spin the rear tire so quickly.

Vice versa, use a small gear in front and a large one in back, and you’ll find it very easy to pedal but very slow going, because now the rear wheel is spinning fewer times per pedal revolution — maybe not even once. This is useful for going up hills and against the wind, where you need extra energy to overcome gravity or air resistance.

The importance of these lower gears cannot be overstated, for there is one preeminent principle governing bicycles, known simply as the First Law of Bicycling:

No matter which direction you ride, it’s always uphill and against the wind.

Unfortunately, it’s good for you.

Exercise is physical exertion for the purpose of improving physical fitness. (If it’s for any other purpose, we call it “hard work.”) Modern fitness programs got their start in Prussia in the 1800s (which should tell you something). Feminists took up the idea to prove that women are not frail, and in fact the word “calisthenics” was coined in 1831 by the headmistress of an American girls’ school, from the Greek words kalos, “beautiful,” and shenos, “strong.”

The primary component of all exercise, from jogging to marathon ballroom dancing, is the contraction of skeletal, or “voluntary,” muscle. Hard-working muscles require more blood, carrying more oxygen. This means both the circulatory and respiratory systems have to work harder, which, over time, improves their efficiency.

The best place to see this improvement is in the people who exercise the most: trained athletes (such as the ones profiled in the IMAX film To the Limit, playing through the end of June in the Kramer IMAX Theatre at the Saskatchewan Science Centre–this is a plug). Athletes’ hearts are generally larger, beat slower and pump more blood than non-athletes’. Athletes are also up to three times as efficient as non-athletes at extracting oxygen from their blood. All of this means that during exercise athletes’ hearts are able to meet the increased demand without working as hard.

Assuming you’re not mountain-climbing while you read this, you’re consuming 250 to 300 millilitres of oxygen a minute. An endurance athlete at peak exertion consumes 20 times as much, more than six liters a minute. One liter of oxygen consumed corresponds to about five kilocalories of metabolic energy. (A kilocalorie, the energy required to raise the temperature of one litre of water one degree Celsius, is a “food” calorie.) So at peak exertion, an athlete is consuming 1,500 to 1,800 kilocalories an hour.

In the process the athlete’s endurance-trained muscle also burns less carbohydrate and more fat than does untrained muscle: another benefit, since the percentage of body fat, experts say, should not exceed 16 to 18 percent in men and 18 to 22 percent in women.

All of these benefits apply primarily to “aerobic,” or “oxygen-using” exercise, such as jogging. Weight-lifting, sprinting and other exercises that depend on quick bursts of intense effort instead of endurance overload the metabolic reactions that provide oxygen to muscle and make use of other biochemical reactions, instead. “Anaerobic” (non-oxygen using) exercises quickly build up compounds in the muscles that lead to fatigue. They build muscle strength, but do little to improve overall cardiovascular fitness.

Exercise has other effects. Body temperature increases: contracting muscle cells may increase total heat production 10 to 20 times. Rectal temperatures of 41.1 C have been recorded in long-distance runners–a temperature the body’s sweating mechanism would never allow for a person at rest: dehydration or even heat exhaustion would set in first. No one knows why the body allows such high temperatures during exercise, but there is evidence that skeletal muscle works better at temperatures above the “normal” 37 degrees.

In the longer term, exercise even helps offset aging. Older people who exercise, studies show, can maintain the capability to climb stairs or walk with as much vigor as an inactive person 20 years younger. Lean body mass, the percentage of the body that’s not fat, invariably decreases with aging, but exercise can help slow that process.

Exercise also appears to boost high-density lipoproteins in the blood. This is the so-called “good cholesterol, “good” because a high ratio of HDL to total cholesterol lowers heart disease risk. In one study, 60-year-old endurance athletes had a ratio of total to HDL cholesterol levels as low as for trained runners in their 20s.

Exercise also appears to improve psychomotor skills such as reaction time and balance. Another study showed 70-year-old women who had been regularly exercising for years had reaction times equal to those of inactive college women.

Weight-bearing exercises such as running and walking even appear to benefit the skeleton; research has shown men and women over 50 who have been running for years have spines 40 percent denser than a sedentary group of the same age.

The big picture? Exercisers live longer. (All right, who said, “At least it feels that way!”?) More than 3,000 healthy women who visited an aerobics clinic were studied for eight years; those that were less fit had a mortality rate 4 1/2 times that of the fitter women. Another study of 17,000 Harvard alumni found that over a 12 to 16-year period, those who had expended 2,000 or more calories a week in physical activity had a 28-percent lower death rate than their less active counterparts, equivalent to 2.15 years of added life.

“A sedentary person who goes into training can produce a response that may be the equivalent of a 10-year or even a 20-year rejuvenation,” says Dr. Roy J. Shephard, director of the School of Physical and Health Education at the University of Toronto.

Better health, more strength, longer life: there’s just no doubt about it–exercise is good for you.

So I do it.

But I still don’t like it.