Imagine the loneliness of the long-distance swimmer, stroking through rough, choppy channels between the Hawaiian islands for hours and hours and miles and miles.

Swimming long distance is unlike any other sport. You can't talk to anyone, you can't hear anything and, at night, there is total sensory deprivation.

We talked to two women, with a 40-year age difference, about how they prepare for and survive channel swims. Here's what we learned ...

MACKENZIE MILLER, 19

Studying interior design at the Art Institute of California in Orange County

Channels swum

2004: Lāna'i to Maui (8.8 miles)

2008: Lāna'i to Maui

2008: Attempted the English Channel (21 miles)

2009: Moloka'i to O'ahu (26 miles)

Training regimen

Normally, she swims, lifts weights and does land-based cardio three times a week. When training for a channel swim, she swims aggressively until she's three-quarters of the way into the swim, peaking at a point that's half the distance of the channel. During the last quarter, she tapers off so she won't tire herself out. To prepare for a planned Catalina swim she must train in cold water.

Obstacles

Storms, unsafe weather, Portuguese man-of-war, extreme currents.

Nutrition

When training for a channel swim, Miller goes for additional carbs, Gatorade, more meats and other proteins.

Sleep

"Sleeping doesn't really change other than going to bed earlier or waking up earlier for training swims. I would definitely say the youth keeps me going."

Next goal

To swim from Catalina Island to the California mainland.

Is your body built to swim?

"By staying with one sport for more than half my life made it in shape."

Advice to others

"Stay positive. Don't ever doubt anything for a second, just keep focused on the end result. Always have a positive mindset during all training sessions."

Fun fact

"My parents dropped me in the ocean when I was about 2 weeks old and I have been swimming ever since." Her father, Mike Miller, is also a channel swimmer who has completed the Catalina to California swim.

LINDA KAISER, 59

Has her own business cleaning pools.

Channels swum

1989: Lāna'i to Maui (8.8 miles)

1990: Maui to Moloka'i (8.5 miles)

1991: Moloka'i to Lāna'i (9.3 miles)

2001: Kaho'olawe to Maui (7 miles)

2003: Kaua'i to Ni'ihau (17 miles)

2005: Kaho'olawe to Lāna'i (17 miles)

2007: Moloka'i to O'ahu (26 miles)

2009: Big Island to Maui (30 miles)

Training regimen

In the O'ahu Club's 50-meter pool, she trains in hours, not miles: Mondays and Wednesdays, five hours (two in the mornings and three in the afternoons); Thursday, three hours; Friday, two hours; Saturdays, up to eight hours in the ocean, depending on her training needs. On Sundays, she does half of her Saturday swim.

When just days away from a channel swim, Kaiser swims about half of what the entire swim will take. If it's anticipated to be a 15-hour swim, for instance, she'll train for eight hours.

She also runs, bikes, lifts weights and paddles a one-person canoe. "At the end of training, you have no social life," she notes. "I have to go home and go to bed."

Obstacles

"You are at the mercy of all the elements: currents, high winds, surf, extreme tides, jellyfish, sharks."

Nutrition

"Nutrition is huge. You have to train your body to fuel you." When training for a channel swim she eats more protein than carbs. "My body tells me what it wants to eat, and it's often a good steak."

Sleep

When in training, eight hours a night is important. She also takes a 15-minute nap in the afternoons. "I have no social life. I swim, work, swim, nap, walk the dog, eat dinner, sleep."

Next goal

To focus on one-man canoe paddling and paddle from Moloka'i to O'ahu.

Fun fact

Born and raised in Hilo, Kaiser was taken into a hot springs by her father when she was less than a year old. She's been a water baby ever since.

Advice to others

"Get out in the ocean. The ocean changes every second and there's always so much to see, it's mesmerizing."