Are you really getting enough exercise?

Resistance machines can provide safe, effective strength training. Image: Thinkstock

To get the full benefit of your workout, you need to know how hard you're exercising, and that can be different for everyone.

The national exercise guidelines are pretty general. They recommend 30 minutes of moderate aerobic exercise on most days and strength training on two to three days each week. But what does this mean to you as an individual? As it turns out, fulfilling the exercise requirements may depend on several things, including your age, resting heart rate, muscle strength, and present level of conditioning.

What is exercise?

Dr. Howard Knuttgen, research associate in physical medicine and rehabilitation at Harvard-affiliated Spaulding Rehabilitation Hospital, says that having a full understanding of what you're doing when you exercise is important. He defines exercise as any activity requiring you to generate force by using your muscles. The more force you exert, the more exercise you get. In general, aerobic, or cardiovascular, workouts call for moving your body (for instance, by walking, running, cycling, rowing, or swimming), and strength-building workouts involve moving an object (for instance, by lifting weights or using resistance machines).

Getting enough aerobic exercise

Two keys to cardiovascular conditioning are intensity and amount. Exercise shouldn't be effortless, but it shouldn't bring you to the brink of collapse.

Intensity. The guidelines suggest brisk exercise, but what does that mean? A brisk clip for some people can be a snail's pace for others. Fortunately, your body offers some clues. The most commonly suggested measure is whether or not you can carry on a conversation while you are walking or running. If you can't, you're probably exercising too strenuously to keep going for 30 minutes and should slow down. But if you can sing, you probably need to step up your pace.

Duration. Recently, high-intensity workouts as brief as four to seven minutes have been promoted as a way to keep fit. Dr. Knuttgen is very skeptical. He has a file of articles and ads promoting exercise regimens that offer to keep you fit with little investment of either time or effort. "This is exercise quackery. If a program sounds too good to be true, it probably is," he says. The same goes for skimping on the number of weekly sessions. "Exercising once a week won't contribute much to your fitness; two weekly sessions should have considerable value; but three are desirable," he advises. "A greater number of exercise sessions per week should provide even greater benefit."

Making strength training count

The national guidelines for strength training are less precise because individual goals can vary depending on whether you need stronger arms, legs, or core muscles. The effectiveness of strength training for any muscle group is based on the amount of weight you lift and the number of times you lift it before fatigue, also known as the repetition maximum (RM), sets in. "If you can lift a weight 20 or 30 times without any problem, you're not building much strength," Dr. Knuttgen says. He advises aiming for five to 15 repetitions as your RM and doing two to four sets of each exercise, resting between sets. Once you can do five to 15 repetitions easily, it's time to add more weight.

It may save you time and money to go to a fitness facility to get started on an exercise program. A certified trainer at a good exercise facility can help you assess where you need to build strength and teach you how to use the equipment to help you achieve it. Moreover, the equipment at a gym has several advantages:

• Most machines have safety devices.

• The machines are designed to help you maintain the right form while exercising.

• The equipment makes it easy to add weight or resistance as you progress.

• Most machines are designed to vary the weight lifted throughout the range of motion of an exercise so that the challenge to the muscle remains optimal.

These days, gym membership isn't only for the young or elite. Many health plans subsidize membership in a fitness club, "Y," or gym, and these facilities often have membership discounts for seniors. You may also want to consider joining a women-only gym if you're shy about exercising or sweating in public.

Finding the time

The hardest part of exercise is probably finding the time to do it adequately. Consider alternating between walking and strength training, walking briskly to the gym on days you do strength training, or trading 30 minutes of television for 30 minutes of exercise.