Stretch every part of the body before launching into a workout. Do 100 sit-ups every morning to get six-pack abs in six weeks. Drink a bottle of water every mile during a marathon.

Really?

Scientists are increasingly finding that many of the “common truths” we hold about exercise and the human body are in fact pretty inaccurate. Static stretching actually tends to weaken muscles (at least pre-workout); sit-ups place undue strain on the spine; and over-hydration can lead to dangerous consequences. It’s these myths and more that Gretchen Reynolds aims to bust in her book “The First 20 Minutes” and her e-book “The First 20 Minutes Personal Trainer.”

A former competitive runner and cyclist, Reynolds runs The New York Times‘ Phys Ed column, where she writes about the latest findings in exercise science. In her books, she takes a broader look at the importance of being physically active, and why even a few short walks every day can make a huge difference in our long-term health and happiness.

Greatist caught up with Reynolds to discuss workouts that don’t involve running, why exercise doesn’t always lead to weight loss, and what it really means to be physically fit in today’s society.

Gretchen Reynolds Interview

What prompted you to write these books in the first place?

What I really wanted to do with the book and also the e-book is look at the broader topic of what we know and don’t know about the human body and how to make it work well. Selfishly, I’m very interested in topics like whether exercise will keep you from developing dementia. I didn’t want to do a book or a column just for competitive athletes. All of us need to be moving and it’s about why we need to be moving and how we can do it well and effectively.

There are so many myths in this book that you bust. Is there one you think is the most prevalent?

Stretching. The evidence is really persuasive that [stretching] does make muscles less strong, less ready for exercise. It doesn’t mean never stretch; it also doesn’t mean that if you love stretching you have to quit. What it means is science shows that it might not be preparing you well for exercise. People get really mad at me; I get hate mail about stretching. And one of the things that the scientists showed is that when you randomly assign people to not stretch, if they firmly believe that stretching is important, they will usually report that they have gotten very sore or have gotten injured, whether doctors can confirm that or not.

Do you think the idea that being “healthy” means exercising all the time intimidates people into not even starting?

Virtually all the exercise scientists that I talk to, I frequently ask: Why do you think most people in America don’t actually exercise at all? And many of them say one of the biggest problems is people hate the word “exercise.” They perceive it as something that they have to do in chunks of hard running.

There is a recent attempt to tell people you don’t have to do it in one chunk — you don’t have to run. That’s another thing a lot of people almost immediately think, that exercise means they have to train for a marathon. Gardening is a perfect physical activity; walking obviously is something almost everyone can do and the human body is very, very good at it. There is almost no evidence that we need to do exercise in a long chunk to get benefits, and in fact there’s very good evidence that walking three times a day is probably healthier than walking once. You get better control of blood sugar, better control of blood pressure, and you tend to actually lose [more weight].

What does it mean to just “listen to your body?”

The human body is actually really well-tuned to be healthy if we leave it alone, which we don’t. Thirst is a beautifully tuned mechanism to make sure you stay hydrated. If you actually pay attention to when you’re thirsty and not thirsty you will generally be almost certainly hydrated. So listen to your body. The same is true with things like movement. The problem is by the time you’re 35 years old and overweight and have thrown many of the physiological systems out of whack, you can’t listen to your body.

In the book you present compelling evidence for why exercise doesn’t always lead to weight loss, even though that’s a key motivator for lots of people. How long do you think it’s going to take for this research to become common knowledge?

People start exercising and do not immediately — or even for a longer term — lose the weight they expect, so they quit exercising. So, it is important to somehow get the message out that if you do not control your eating habits, if you do not cut calories, exercise almost never leads to weight loss by itself. And that’s especially true for women. It’s really unfair. But exercising does seem to stimulate the appetite more in women than it does in men. It’s not uncommon at all for women who join marathon-training groups to gain weight. And that can be really discouraging. What is important to understand is if you are taking in fewer calories than you are burning you will lose weight. And once you’ve reached the weight you want to maintain, exercise has been shown to be the best way to maintain a reasonable weight. It does help your body essentially reset its sense of how much you should weigh and it stops producing as many appetite hormones.

How do you define the terms “health” and “fitness”?

The medical definition would be you’re healthy if you don’t have diabetes or dementia or heart disease. I think “health” needs to be defined a little more broadly in terms of being able to do the things you want to be able to do. What you get from exercising, however you define that, is the ability to have a fully functional life. You can walk wherever you need to walk, you can pick up your laundry when you need to, you can lift your children if they’re still small enough. And you do not have the major diseases of modern Western life; you don’t have diabetes, heart disease, or dementia.

Follow Reynolds on Twitter for the latest findings in exercise science.

Do you agree with the fitness myths that Reynolds is busting? Let us know in the comments below or tweet the author at @ShanaDLebowitz.