Tony Robbins explains how he sustains a massive amount of energy with no stimulants and little sleep

After an intense 120-day seminar tour when he was 39 years old, Robbins felt more drained than he ever had in his life. He said that one of his friends told him, "Dude, you're 39. Most athletes retire at 40... It's not like you're going to be doing this when you're 42."

Robbins started to doubt himself. But, being Tony Robbins, he decided to seek out the world's oldest extreme athletes and figure out their secrets.

One of the people he met with was Catholic nun Sister Madonna Buder. Now 85, she is a member of the Triathlon Hall of Fame, and has completed 45 Ironman races and more than 350 triathlons. She was not remotely an athlete for the first half of her life, and only began her athletic career at age 40 after a priest recommended running as a spiritual exercise.

And that's what Robbins found most remarkable. In her book "The Grace to Race," Buder explains that she never considered her age to be an impediment to her athletic progress, and that she has been driven by the spiritually uplifting nature of pushing herself physically.

Robbins also found nearly all of the exceptional athletes above the age of 65 he interviewed paid careful attention to their nutrient levels through blood tests.

It inspired Robbins to start getting a blood test every six months rather than annually, and to use the results as a guide to adapt his diet to whatever nutrients he had too much or too little of.

Robbins said he keeps his diet pretty basic, with a focus on green vegetables and fish. He doesn't consume caffeine, alcohol, nicotine, or recreational drugs because he said he wants to keep himself conditioned the same way a professional athlete does.

Robbins is also a huge fan of the NuCalm system.

A neuroscientist named Dr. Blake Holloway designed the device as a way to treat patients with post-traumatic stress disorder, but found that he actually had a market with dental patients who suffered from intense anxiety while in the dentist's chair.

The system includes headphones that play relaxing music, light-blocking glasses, mild electric nodes for the throat, and a GABBA amino acid supplement. It looks like something you would buy at a magic shop, but besides dentists, it's also used by the Chicago Blackhawks NHL team and has been deemed effective at enabling patients to enter a deeply meditative state by Dr. Chung-Kang Peng, Ph.D., co-director of the Rey Institute at Beth Israel Deaconess Medical Center/Harvard Medical School.

When we recently spoke with Robbins, he said that in the previous day's media circuit, he had just a half hour window of free time, and he chose to use the NuCalm system for 20 of those minutes and felt rejuvenated.

The main takeaway: If you can find a way to enter a deep meditative state for 20 minutes, your body may feel refreshed and rid of debilitating stress.

Robbins also has a morning routine that he makes at least 10 minutes for every morning.

If he's at one of his several homes around the world, he'll start off the day by immersing himself in one of his cold plunge pools for one minute or spending three minutes in a full-body cryotherapy tank. When the body's external temperature drops drastically and suddenly in this way, inflammation decreases and the brain experiences a rush of endorphins.

Then he does his "priming" ritual, which consists of three minutes of a deep breathing exercise, three minutes of expressing gratitude for three specific things in his life, and three minutes seeking strength and wishing good things for his family, friends, and clients.

Robbins said that he places such importance on his energy levels because, "If you don't have energy, you're gonna have no passion in your [romantic] relationship ... If you don't have any energy, you can't do a great job with your kids because they have more energy than you do. If you don't have energy, you're not going to run your own business, much less multiple businesses."

"Energy is life," he said.