When it comes to running, or any fitness feat for that matter, it’s not just about how well your body performs; it’s also about your mental strength. And that is exactly what Olympic bronze medalist and long-distance runner Deena Kastor, 45, talks about in her new memoir, Let Your Mind Run ($27; amazon.com), on bookshelves today.

“Our choices, thoughts, and perspectives are the drivers of our physical ability,” explains Kastor, who is racing the Boston Marathon next week. “A pessimist might have the ability to reach their goals, but decades of positive psychology would support that optimism makes reaching your goals easier—and may also give you the ability to reach beyond what you’ve ever expected out of yourself.” Here, Kastor shares some of the mindfulness techniques she’s learned over the miles.

On training holistically

“There are so many training programs out there that talk about mile repeats, tempo runs, long runs. I thought that my greatest asset was my mind, and learning how to cultivate it. All the talent in the world isn’t going to get you anywhere because we need to pay equal attention to our minds and our bodies. So many of us obsess about training plans and what is going to get us to that finish line, and I will tell you now that the physical training is not going to reach your potential if you are not cultivating a strong mind to get there.”

On tuning into your thoughts

“We produce over 50,000 thoughts a day that shape our perspective, our voice, and our actions. I take advantage of all of these thoughts to ensure they are leading me in the direction I want to go. First, I pay attention by listening to my mind’s reaction, and then, I analyze how I might shape the thought to strengthen me.”

On the power of gratitude

“Instead of dreading a difficult task such as training or deadlines, I think of how grateful I am for the opportunity to extend my limits or share my perspective.”

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On being accountable

“Sometimes when I’m challenged, I can easily justify compromising. But it’s not just about the immediate goal, and more about creating mental habits of persistence, resilience and commitment. In training, every time I choose courage over fear, or persistence in the wake of challenge, I know I am building myself more capable to handle challenges in life.”

On always learning

“What I learned throughout the years of trying to twist my thoughts and be better, stronger, more grateful—all these attributes of positivity that have helped fuel me is that that the process is never-ending. Even on a flight delay coming out to Washington earlier this week, my first thought was, 'Damn it!' But then I was like, 'Oh, now I can try that café I passed.' And so it’s just always twisting that, and running has taught me that. But, it is certainly most valuable in life.”

On embracing struggle

"That struggle in the marathon is my favorite part of the race. When it gets there, my first thought is ‘Oh no,’ and then I remember this is where I get to do my best work. This is where I get to shine and get better, be better than the person I am in this moment. I get to push my physical boundaries, my mental limits; and I really have fun in those moments. And sometimes it just takes telling yourself that you can get to the next mile, and when the next mile seems unbearable, it’s the next light post, and when that doesn’t seem possible, you say ‘OK how about one step at a type.’ And when that seems excruciating, you think 'let’s look at the signs everyone is holding on the sidelines and completely distract yourself.' So it is just working through all of those tools to try and get to that place that gets you to the finish line. And sometimes you have that epiphany and feel amazing and sometimes you just keep working until you get to the finish line—and you get the to end result that you are working toward nonetheless."

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On finding the positive in negative

"I remember thinking about how disappointed I was after a race—and long ago, I used to own that disappointment, and disappointment meant I was a failure. And it took some twists and turns, and now disappointment means to me that I really care, and I know I have better in me, and let’s get to better and how do we do that. So it’s just showing that some of these negative terms in our lives could actually be rooted in positive meaning that can be springboards for you. A lot of it has to do with having a growth mindset versus a fixed mindset. Like disappointment means this is as good as I am and I am a failure, whereas disappointment can mean you want to do better, this is where I am, how can I go after it and get better from this moment. What you did wrong, what you did right, and then move on from it."

On owning your power

“Our minds are shapeable, trainable, and deserve the same, if not more attention than our physical bodies.”

On sharing your gifts

“In the dedication of my book, I dedicated it to my coach, Joe Vigil, at the time. He was my first professional coach and he coached me for eight years. He taught me that the value of everything that we have, all that we possess—whether time, money, knowledge, food—the value of it increases exponentially the moment it is shared, and I love that. If you have an abundant harvest in your garden, there is nothing better than sitting around the table and preparing beautiful meals to share with family and friends. When your days are busy, there is nothing like sitting down and sharing a cappuccino with a friend who is also trying to find time to connect. With all that we know, the truths that we find through running, life, our work—sharing that with others is such a valuable and empowering process."