Media playback is unsupported on your device Media caption Peter Bowes joins the workout at the Results Fitness gym

Bombarded with adverts promising a longer, healthier life, BBC News Los Angeles correspondent Peter Bowes goes in search of eternal youth.

Are you a jogger or a weight lifter? Do you run marathons or take part in triathlons. When it comes to breaking a sweat, each to their own. But what kind of exercise is best if you want to live longer? In particular, is shorter and sharper better than longer and duller?

According to Dr Stuart Gray from the University of Aberdeen's musculoskeletal research programme, a key factor in reducing the likelihood of early death from cardiovascular disease could be high intensity exercise.

"The benefits do seem to be quite dramatic," he says.

He admits, though, that many in the medical establishment are still promoting moderate intensity exercise.

Gray's study has shown that short bursts of activity, such as sprinting or pedalling all-out on an exercise bike for as little as 30 seconds, result in the body getting rid of fat in the blood faster than exercising at moderate intensity, such as taking a brisk walk.

And getting rid of fat in the blood is important as it reduces the chances of suffering a heart attack.

Image caption High intensity exercise is designed to burn fat

The early morning workout at Results Fitness in Santa Clarita, California, puts the claims for high intensity exercise to the test. The gym, owned by husband and wife Alwyn and Rachel Cosgrove, bases its classes on the latest research from medical journals.

The Cosgroves treat their gymnasium as a fitness laboratory.

Instead of people learning to exercise either from a trainer at their gym, or a friend, or from a magazine, Alwyn Cosgrove wants to bring the latest research to bear on how we should be exercising.

"The medical database is full of stuff that works. All we are doing is putting it together and trying to make something better," he says.

The metabolic zone class, a 45-minute interval training session, is designed to burn fat. Everyone wears a heart-rate monitor and works at their own pace, according to their body's response to the workout.

"We want to get them up to 85% and above of their maximum heart rate," says Rachel Cosgrove.

My body is my machine and if I do not take care of it no-one else will Cyndi Madia, Gym-goer

The class includes explosive exercises, such as slamming a medicine ball on the ground at high speed. After a rest period, when the heart rate should drop to 75% or below one's maximum, the next round starts.

"Research has shown that the interval effect - when you are working at an intensity that you could not hold longer than a couple of minutes followed by full recovery - is when you are going to get the best results when it comes to fat loss and increasing your metabolism," says Rachel Cosgrove.

"We have been open for 12 years and we have tracked every single workout that our clients have done. In line with the research, the shorter, intense workouts are what give our clients the biggest bang for their buck."

Cyndi Madia, 42, a busy mother with a full-time job in a school, enjoys the early morning workouts. "My body is my machine and if I do not take care of it no-one else will," says Madia.

"I have seen my parents falling apart at 60 and saying they are old. I do not want to be be like that."

High intensity training (HIT) Dr Jamie Timmons, professor of ageing biology at Birmingham University, says that with just three minutes of HIT a week for four weeks significant health benefits can be achieved. HIT can help aerobic fitness, that's your lungs and heart's ability to get oxygen into your body. It also helps improve insulin sensitivity. Insulin removes sugar from the blood and it controls fat. Despite HIT's benefits some people, for genetic reasons, will respond much less to HIT than will others.

Worries about growing infirm are shared by another gym-goer Alecia Menzano.

"My mother will be 83 in March. She has never enjoyed any physical activity, she has had a hip replaced, she's got severe arthritis. I don't want to be like her, confined to a wheelchair and unable to get on to the floor to play with my grandchildren," says Menzano.

James Madia, a 51-year old police officer, has been working out in gyms for more than 30 years. To his surprise in the past two years he has seen his body fat drop from 26% to 10% by using the Cosgroves' high intensity approach.

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"Coming from the guys' gym environment, where you are pumping iron, it did not seem all that serious," he says.

"Then I took a class and almost crawled out of here on my hands and knees and realised, 'Okay, this is harder than it looks.' It definitely is challenging."

In the absence of long-term controlled research on human beings, the impact of exercise on lifespan is difficult to quantify. However, a study published in The Physician and Sports Medicine suggests that older athletes on intense training programmes are capable of achieving remarkable levels of fitness. MRI scans have shown that a 70-year-old triathlete can have as much muscle mass as a 40-year-old.

"The idea is to create this organism, this human being, that can continue to function late in life," says Alwyn Cosgrove.

"My gut instinct is that if I improve the quality of every single day from a nutrition level, from an exercise level, and by just building the strength in the body, that perhaps, I can extend lifespan."

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