(MONEY Magazine) – The week after Labor Day, I got down to some serious retirement planning: I raced in five events at the 2006 World Masters Rowing Regatta, a competition that attracts some 3,000 rowers with an average age of 50 from 36 countries.

What in the world, you may ask, does going backward down a 1,000-meter course yanking as hard as you can on an oar have to do with preparing for retirement? Well, I consider physical and mental fitness an integral part of true retirement planning, and I think you should too. After all, studies show that good health is one of the key drivers of happiness in retirement. What's more, staying in decent physical shape increases your odds of achieving financial security.

For one thing, the healthier you are, the longer you'll likely be able to save for retirement. Research from the Employee Benefit Research Institute (EBRI) shows that four in 10 people end up leaving work before they want to retire, about 40% of the time because of health problems or a disability. As the chart below shows, that sort of involuntary early exit can seriously stunt the size of your portfolio, dramatically reducing the annual income your savings can generate.

Healthy people also tend to be more self-assured about their finances. When EBRI asked workers how confident they were that they would have enough money to support themselves comfortably after they retired, 79% of those in excellent or very good health said they were very or somewhat confident vs. only 35% of those in fair or poor health.

And, although there are no guarantees, staying healthy and fit means you'll likely shell out less on doctors, prescriptions and other medical care later in life. That can be a huge financial leg up, considering that Fidelity Investments estimates that the average 65-year-old couple retiring today will spend $200,000 on medical costs in retirement. That number doesn't even include the $60,000 to $150,000 a year that assisted living or nursing-home care might cost you.

Healthy and Wealthy

Investing time and effort in staying fit can pay dividends that are every bit as valuable as those you earn on your portfolio. Here are my tips for getting started, plus the best free resources I've come across.

• DEVELOP A WORKOUT PLAN For the biggest payoff, concentrate first on aerobic exercise. Ideally you want to get your heart beating at 75% of its maximum rate per minute (your max is roughly 220 minus your age) for 20 to 45 minutes three times a week. Next throw in resistance or weight training to build muscle and bone strength, and stretching to stay limber. For details on how to create a workout, check out Exercise: A Guide from the National Institute on Aging, an 86-page booklet you can download free at nia.nih.gov (click on Publications, then Healthy Aging). Another useful resource is Growing Stronger: Strength Training for Older Adults from the Centers for Disease Control (type "growing stronger" into the search box at cdc.gov).

• SET A GOAL Just as having a retirement income to aim for helps you focus your financial plan, having attainable fitness objectives will increase the odds you'll stick to your regimen. What's a reasonable goal? That's for you to say. It could be as simple as reducing your weight or cholesterol. For help monitoring your progress, take Shape Up America's tests of strength, flexibility and aerobic fitness (at shapeup.org, click on Shape Up, then Fitness Center, then Assessment).

• STAY MENTALLY SHARP Maintaining your physical fitness should help keep your mind agile. But research also suggests that you may be able to stay more mentally alert later in life by cutting down on passive activities like sacking out in front of the TV and instead engaging in more stimulating pursuits. "People who do more robust cognitive activities tend to end up with less dementia," says Dr. John Trojanowski, director of the Institute on Aging at the University of Pennsylvania. For tips on keeping your brain sharp, read Mental Fitness for Life: 7 Steps to Healthy Aging ($16.95).

As for me, the crews I rowed with medaled in two out of our five races. My goal is to pick up more "hardware" next year. If I don't, well, the Masters Regatta includes events for rowers 75 and over, and four oarsmen well into their eighties competed this year. I've got plenty of time.

PHYSICALLY FIT, FISCALLY FIT

Retiring just five years early because of health problems takes a heavy toll.

NOTES: Assumes worker who retires at 65 had $500,000 in 401(k) at age 60, saves $20,000 a year and earns 8% annually. Income based on 4% initial withdrawal, adjusted for inflation. SOURCE: MONEY research.

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