Sex, like exercise, releases endorphins. Endorphins contribute to runner’s high and diminishes pain levels.

An active sex life may help us live longer, too. Dr. David Weeks, a clinical neuropsychologist at Scotland’s Royal Edinburgh Hospital, conducted a study of 3,500 people ranging in age from 18 to 102. Weeks concluded that sex actually slows aging process.

Sexual therapists remind us that frequent sex is a form of exercise. And feeling secure in a relationship leads to feeling happier, which could lead to greater health--and a younger look.

In fact, these studies indicate that intimacy plays a key role in health benefits of sex. A promiscuous sexual relationship may actually produce an opposite effect by introducing a sense of anxiety and fear.

In spite of all these health benefits and sheer pleasure of act, Americans may still need a boost. At least one-third of American couples report "inhibited sexual desire," according to The Masters and Johnson Institute.

Sex therapists say sex acts on principal of "use it or lose it." So, for your heart, mind, and soul, best advice may be to "Just do it!"

3. How much do you charge and how do you expect payment?

Prices for personal fitness instruction vary widely based on where you live and trainer qualification and experience. As with everything else, you usually get what you pay for, but there’a no guarantee that most expensive trainer will be best suited for you and your goals.

Talk to other people who have used fitness trainers. Or call health clubs near you to determine average rate in your area. If trainer is meeting you at your home, expect to pay slightly more than average. If you are meeting at a health club, prepare to cover cost of a guest fee if there is one.

Get specifics on all fees and how payment is to be made. Some trainers charge on a per session basis, while others offer packages and discounted rates for a given number of pre-paid sessions. Some accept only cash. Others accept checks and credit cards. Most fitness trainers have some sort of cancellation policy. Agree on all financial obligations before first session and insist that both parties sign a billing contract.

Avoid at all costs trainer who responds to a question about fees with statements like "How much can you afford?" or "How much are you looking to spend?" This is someone who has their wallet—not your fitness goals—in mind.

5. How do they look?

You should never base your selection solely on physical appearance. A person with a flawless-looking body may not know first thing about safely teaching you how to achieve your own goals. This is especially true if they have achieved their own results through things like drugs, eating disorders or exercise obsession.

The person you hire will be teaching you skills and lifestyle habits and doesn’t need to look like a model in a fitness magazine. But trainers do need to practice what they preach. Let’s face it. Are you really going to respect someone’s opinion if you’re in better shape than they are? Probably not.

6. What’s your comfort level?

Above all, make sure you choose a trainer with whom you feel comfortable and whether their personality is a good match with yours. Above all, trust your instincts. Hiring someone with superior training knowledge is worthless if you don’t feel comfortable. You need to trust, respect and feel at ease with them.

You wouldn’t buy a pair of exercise shoes without at least trying them on to see if they’re comfortable. The same concept holds for hiring a personal fitness trainer. Set up an interview, ask right questions, and follow your instincts for perfect fit.