One of the things that never fails to amaze me is how often some precious belief I have turns out to just be a myth. Well, myth is a tough word because some of the meanings of "myth" are important, like: A legend or story that explains or demonstrates a virtue or message.

An example of that would be the story of Marine Gunnery Sergeant Dan Daly who shouted to his men, "Come on, you sons of bitches, do you want to live forever?" Odds are pretty good he actually said this during World War I at Belleau Wood as he won two Medals of Honor, and Marines ever since have remembered him as a model of courage and victory against nearly insurmountable odds.

These kinds of myths are good for our souls and give us models for how to live and overcome adversity. The myths that seem to die hard and need to be put to sleep are defined as: false or unproved collective beliefs ... say, something like stretching before you work out or compete.

I can't tell you how many hundreds of different types of stretches I have put classes through. Wrestlers, cadets, training buddies—we have stretched together thousands and thousands of times in my life, often at my direction, and now science is telling me it was of no benefit at all prior to performing; any stretching should probably be done after you have worked out or played. Now, if it were just a neutral, "does no benefit," that would be bad enough. But now it seems stretching actually reduces our ability to perform at our best…WHAT?!

Stretching actually inhibits the muscle's ability to perform at its optimum level and this terrible truth was revealed to me (as so much is) while I was reading a book by Gretchen Reynolds called "The First 20 Minutes." As I read I was thinking to myself, "Well, at least we still need to warm up," but as I read on she showed there is no research that suggests even warming up matters. Dang! It seems scientists have been putting a lot of our "common sense" ideas to the test, and some are really turning out to be myths that are not only wasting time, but may be hurting us in the long run.

Thinking that "if a little is good for you a lot will be great" leads to modest gains, maybe, and injury probably. What if I told you that in 20 minutes you could enhance your cardiovascular fitness far better than you would in a two-hour run? R-i-g-h-t, you'd think sarcastically. But I did a little Googling to look into the research results mentioned in the book and there it was…noooooo! Worse, a British study of highly competitive older endurance athletes discovered scarring in their heart muscles, scarring that wasn't present in their non-endurance counterparts.

So is all the news bad? Are all our common beliefs about exercise wrong, just myths? No. But the truths are fine-tuned in this book and make you more likely to get in great shape, or stay that way and remain injury-free, a condition I have had a hard time maintaining over the years. In fact, this book has some truly remarkable research in it that you might start using today.

Let's take cramping. No one likes a cramp and we tend to think it's due to dehydration, so we drink fluids hoping to avoid it or at least stop it once we get one. It turns out science is finding cramping is a result of fatigue not dehydration, and drinking most fluids may not shorten or prevent a cramp…except for pickle juice. Yep, science doesn't know why, but good old-fashioned pickle juice shortens the duration of a cramp. It seems the juice works before it can even be processed from your stomach ... a weird but true fitness fact.

Other facts we need to think about are the effects of exercise, not only on our bodies, but on our minds. In addition to making us smarter, exercise is a great antidote for the ravages of age. Advocates of running have long claimed this, but now research shows that strength training has the same benefits and keeps us stronger for a lifetime. In fact, in one British Columbia study strength training showed superior benefits in cognitive benefit over endurance training in women over the age of 65. So everyone, keep lifting.

Finally, I guess books like this help filter out my false myths. They make me want to learn about the various ways to improve not only my fitness, but the advice I give others to improve their own level of fitness, in a profession that can demand so much in a fraction of a second.

The only tough part is when I find out all the bad advice I have given over the years ... Sorry, cadets.

Dave Smith is an internationally recognized law enforcement trainer and is the creator of "JD Buck Savage." You can follow Buck on Twitter at @thebucksavage.