Health and fitness aren't an afterthought for many successful people; health and fitness play a major role in their success. While the physical benefits clearly matter, the mental benefits -- perseverance, resilience, determination, and mental toughness -- are just as important.

This is the latest in my series where I follow an incredibly successful person's workout plan for one week. (Others include seven-time Nascar champion Jimmie JohnsonDef Leppard guitarist Phil Collen, and ex-Twitter CEO and Chorus founder Dick Costolo.)

This time it's the regimen of Nirav Tolia, the co-founder and CEO of Nextdoor, the social network for residents of over 80% of U.S. neighborhoods and tens of millions of neighbors (and counting.) The company's mission? To bring a sense of community back to the neighborhood.

Nirav has a personal mission as well. "I've been a lifelong athlete," he says, "but my commitment to fitness eroded with the birth of our sons Deven, Dylan, and Declan. I love to exercise, but spending time with my family will always be my top priority. As important as working out is, I would rather be with my family.

"After beginning work with noted CEO coach Fred Kofman, it became clear that reclaiming physical health was a necessity for operating at peak mental capacity, and ultimately I believe, emotionally as well. Health is the foundation for everything we do."

The "peak mental capacity" aspect of health and fitness raises an interesting point. According to Nirav, there are only a few decisions you make in business that have tremendous impact -- and you can't plan for when the need to make those decisions will occur. In those moments, if you're stressed it's very difficult to perform. You can't think as clearly. Your ability to calculate risk is compromised.

For Nirav, the path to optimal performance started with getting back in touch with his physical self. Less than a year later he's lost weight, boasts a body fat percentage of approximately 12%, his resting heart rate is down, his blood pressure is down, his cholesterol markers are better... 

"I've found a sustainable way for me to feel like I can take control, do the things that make me feel good, live in away that I can be around for my kids... and be at my best at work."

Isn't that what we're all looking for? 

Here's Nirav's weekly regimen.

Diet and Nutrition

Nirav follows a personalized version of intermittent fasting, the eating regimen popularized by Martin Berkhan of Leangains.com. (I've written about intermittent fasting before.) "With intermittent fasting," Nirav says, "I find myself focusing less on what I can and cannot eat, and more on when I will eat. Again, it's very sustainable."

In Nirav's case, he fasts for 24 hours starting on Sunday night. (Yep, he starts each week with a 24-hour fast.) Tuesday through Friday he eats between 2 p.m. and 8 p.m, fasting the other 18 hours.  

"You can have a bad meal, or a bad day of meals, and quickly get back on track with a 24-hour fast," Nirav says. "The fast kick-starts your body back into that mode."  

Weekends are family time, so he eats whenever his wife and kids do. Then, on Sunday nights he starts all over again.

He also takes a few supplements: Fish Oil, Vitamin D, Vitamin B12, and Alpha-Lipoic Acid.

"One area where I really need to make progress is sleep," Nirav says. "I currently sleep around five hours each night, and I need to get six to seven hours of sleep. Sleep is just as important as activity -- and I need more of it."

Weight Training

One day a week, typically Wednesdays, Nirav does a 30-minute circuit workout inspired by Dr. Doug McGuff, the author of Body by Science. He's a big believer in high-intensity, low-frequency weight training.

Specific exercises: Chest press, bicep curl, lat pull-down, shoulder press, and chin-ups (which are not typically part of Doug's regimen).

The key to the Body by Science approach is to perform reps reaaallly slowly, keeping muscles under load for an extended period of time, and to keeping working until failure -- which is even tougher in practice than it sounds in theory. (More on that in a bit.)

Cardiovascular Training

"Walking is one of the best exercises," Nirav says, "because of its positive effect on posture, sustainable intensity, and anyone can do it, anywhere!"

Monday through Friday he walks an average of 15k steps per day, which works out to  roughly 7 miles. He uses an Apple Watch to keep track.

And then there's SoulCycle. 

"I was originally a skeptic," he says, "but my wife, an expert regular rider, suggested it as a way for us to spend time together. I quickly became addicted and now take 4 classes per week, sometimes including Saturdays and Sundays.

"SoulCycle is not just great for your physical body -- it boosts your heart and mind. The core of SoulCycle are the instructors, and I have to express my gratitude to RachelTiff, and Ian for making me feel so uplifted after taking one of their classes."

How It Went For Me

Let's start with a 24-hour fast to start the week. I like fasts; if you're trying to lose weight, I think a one-day fast is the perfect way to jump-start the process.

Since on normal days Nirav eats within a 6-hour window and my normal window is 8 hours, I decided to start fasting at noon on Sunday. That way I could eat at noon on Monday, and then my window would be open from noon to 6 p.m. for the rest of the week. (I go to bed fairly early and not eating in the evening is harder for me than holding off in the morning, so I try to make sure my window "closes" a little later.) 

If you've never fasted for 24 hours, here's what to expect. The first 6 to 8 hours won't be a lot of fun, so find things to do to keep yourself occupied. And drink plenty of water; you'll be surprised by how much that helps with hunger pangs.

You'll also be surprised by how little you'll want to eat for your first meal on Monday. While fasting doesn't necessarily shrink your stomach, it does reset your appetite "thermostat" and you'll feel full more quickly than usual. (If you're trying to lose weight, that's a good thing.)

After that, just keep in mind the basic principles of intermittent fasting and you'll be fine. You might feel a little less energetic for a couple of days, but after that your body will adjust and you'll start burning more fat for energy. (Another good thing.) 

I also took the supplements Nirav recommends. While it was too soon to feel any difference, he takes a highly science-based approach to nutrition and fitness, so I'm  onboard for the long haul.

As for lifting, Nirav's routine is very different from what I normally do. I typically lift weights 5 to 6 days a week, so low-frequency is a major change. 

Following the Body by Science principles ensures high intensity, though. In simple terms, the focus is on the amount of time your muscles are under load, not the number of reps you do. That means every rep is done really slowly; the goal is to keep your muscles under load for approximately 90 seconds.

So if you're benching, use less weight than you normally do, lower the weight very slowly (taking at least five seconds), stop just above your chest, hold for a few seconds, squeezing your chest muscles the entire time, then slowly push it back up.

And then do it again, and again.

The goal is to go for approximately 90 seconds until you reach failure -- not mental failure, physical failure. Like Lombardi said, fatigue makes cowards of us all. If you can go for longer than 90 seconds, add weight next time. After all, you won't get stronger unless you progressively increase either the weight you use or the time you spend under load.

Do it right and your muscles will feel like limp noodles. (Yet another good thing.) And you'll get your lifting done in around 30 minutes.

That will give you some time to take those walks. Unlike Nirav, who often walks to work, my daily commute is two flights of stairs, so I had to schedule my walks. That's a lot easier than you might think; I did some radio interviews while walking, was a guest on a couple of podcasts... you can get a lot done while you're walking. LinkedIn CEO Jeff Weiner likes to schedule walking meetings.

I did have to take an 80 to 90 minute walk a couple of days to make sure I got my steps in, but that's okay. In fact it's more than okay if you go for a walk with your significant other.

I also planned the week around a trip so I could take SoulCycle classes; there are no locations where I live.

I like riding bikes, but SoulCycle workouts are different than riding hills and climbing mountains. Not easier, not harder, just different. 

And very, very cool. I liked the community aspect a lot. You ride at your pace, but you do it with other people. SoulCycle incorporates the best parts of group rides: the sense of camaraderie and community... and leaves out the worst parts: the egos and agendas and, well, there's always that one guy....

Nirav is a huge proponent of SoulCycle. Now I am, too. I just wish there was a location near me.

What I Learned

Oddly enough, what I liked most was the walking. It's low impact, helps me focus on my posture (which I need)... besides, humans were made to walk.

But I also liked the high-intensity lifting session. I tend to do conventional sets and reps, usually in a pyramid fashion (going from less weight/more reps to higher weight/fewer reps.) But your body adapts to anything, and making progress gets tougher. Shooting for a time under load of around 90 seconds worked my muscles in a completely different way -- and made me incredibly sore for several days after. (One more good thing in a series of good things.)

As for intermittent fasting, I've gone back to my 16-hour fasting windows. They work for me. But I do plan to include one 24-hour fast a month. Nirav is right: It's a great re-set, both physically and mentally. I'm a big proponent of "If I can do that, I can certainly do this" thinking. 

When you need to do something difficult, knowing you've done other difficult things makes what you're facing much easier. Confidence is earned, and one of the best ways to develop confidence is to put yourself in situations where you have to earn it.

And that's the best lesson of all from this experience. You can't improve if you don't try new things. Try Nirav's plan for a week. Try one of the others. Try what a friend does. And then decide, based on the results, how you'll incorporate some of those things into your life. 

You don't have to follow Nirav's regimen, but you should try to do what Nirav has done: Find a sustainable way to take control, to do the things that make you feel good, to live in away that you can be around for loved ones... and to be at your best at work.

That's what being healthy and fit is really about.