Much of what we think we know is based on myth. We hear something when we’re kids, it gets repeated a few times, and before you know it, it’s “fact.” In fitness, just like every other facet of our lives, there are as many myths are there are truths. Whether it's collective misinformation carried on through generations or simply changing knowledge, many of the adages we take for fact aren't factual at all. Here are some of the more common fitness "facts" that are more old wives' tale than reality.

1. You must wait an hour after eating before you swim

The common myth that the blood going to your digestive tract after eating diverts the blood needed to keep your arms and legs pumping during swimming, which leads to cramps and sometimes drowning, is totally unfounded. Advanced creatures that we are, we have enough blood to digest food and properly work our limbs at the same time. And at least one study has backed that up, finding that fewer than 1 percent of U.S. drownings occurred after the victim ate a meal. Experts concede that swimming strenuously on a full stomach could possibly lead to some cramping, but for most casual swimmers the chances are low. So go ahead and hop in after a sandwich, but be wary of the pre-swim cocktail. The Centers for Disease Control and Prevention reports that up to half of all adolescent and adult deaths related to water recreation involve alcohol. 

2. You have to 'cool down' after a workout for best performance

Most coaches and trainers call for a formal period of cooling down after a workout or competition to prevent muscle soreness, improve limberness and speed recovery. But many studies have failed to prove any merit, The New York Times reports. Although “venous pooling” that can lead to dizziness may occur after the end of an especially grueling workout, a two-minute walk will negate that — which is not really a full “cool down.” As well, some suggest that there may be a “returning to normalcy” psychological element to the practice — but in terms of soreness and recovery, as of now scientists can’t prove any benefit.

3. You have to stretch before exercise

It’s one of the major tenets of exercise: You must stretch beforehand. But fitness science has done a major 180 on this one. Study after study has found no reduction in soreness after static stretching, and injury prevention doesn’t get any backup from the studies either. Although there are gazillions of adamant stretchers out there, the authors of a comprehensive review of 104 studies on the topic conclude that static stretching as the sole activity during warm-up routines “should generally be avoided.” You will increase flexibility, but the scientific consensus is that pre-exercise stretching is most-likely unnecessary and counterproductive.

4. No pain, no gain

We have Jane Fonda, the queen of the baby boomer fitness craze, to thank for this adage. She and many other instructors of her day told video viewers to “feel the burn” and encouraging them on with the “no pain, no gain” catchphrase, the slogan has become a mantra for those who want to push themselves. But experts disagree. The perception is that if it doesn’t hurt, there is no benefit, and this just isn’t true. Feeling discomfort or emotional fatigue is one thing, but pain? No. "You shouldn't be exercising at a level of pain ever,” says Alice Burron, spokeswoman for the American Council on Exercise. "You want to exercise smarter, not harder," she adds. "That's the premise. You don't have to kill yourself. You just have to be smart about it."

5. Protein bars or drinks after a workout are good

Hydration is the most important part of “recovery” after a workout, followed by carbohydrates and then protein – leading many people to go for the convenience of a protein bar or drink. But many of these snacks contain as many calories as a whole meal, and are little more than glorified junk food (see "7 nutrition bars worse than candy" for the full picture). Instead, go for a carb- and protein-rich snack of real food – like an apple with peanut butter or half a whole-wheat bagel with hummus – to get more complete nutrients, fewer calories and avoid processed ingredients.

6. You need sports drinks to replace lost electrolytes

If you’re running marathons or other high-intensity workouts that last longer than an hour, the added ingredients in sports drinks can be valuable. But many experts warn against the unnecessary calories (and other questionable ingredients) for those doing low-intensity workouts or exercising for less than 30 minutes. Water is important for proper hydration, and most fitness outing don’t call for anything more than that. As for the claims in sports drink ads, an Oxford University study looked at more than 400 advertising claims for sports drinks and could not find scientific backing for more than half of them; they characterized many of the rest as "flawed science."

7. Lifting heavy weights will make women bulk up

The bulging muscles of a bodybuilder are the result of very specific combination of weight training, diet and hormones — and women don’t have the testosterone to get bulky from heavy weight lifting alone. A study at Central Michigan University backs up this expert opinion. Researchers had women work one arm with just a few reps of a heavy weight and the other doing more reps with a lighter weight — both an equivalent number of pounds. The heavy lifting arms got stronger, but the size of both arms remained the same.

8. Sex is great exercise

Sex is great, but not as exercise. Common statistics cite that a roll in the hay burns up to 300 calories per person. But when the numbers are crunched, it’s not so encouraging. A 150-pound man could burn about 250 calories per 60 minutes of vigorous and continuous sex. Since studies reveal that most episodes of sex last a paltry six minutes, the result is about 20 calories burned. Although sex has plenty of other benefits, burning calories is reserved only for lovers of extreme endurance.

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