Rowing is often called the best aerobic exercise because it offers a total body workout and is low-impact.
Rowing involves performing a continuous motion with focused coordination between the arms and the legs. If you've never rowed a boat or paddled a canoe before, it may take some time to get the hang of it, but the fitness benefits are worth time spent on the learning curve.
Home machines come very close to simulating this fun yet strenuous activity, but try different models before you buy. Don't be swayed by price alone: The resistance mechanism on cheaper models often relies on pistons and may not give you the smoothest motion. Check out rowing machines that rely on air, water or magnetic resistance to find the one that feels most natural to you.
While you should feel comfortable on the seat, working with the oars will tell you how well a machine suits you. You should be able to move your arms through a full range of motion. The resistance should feel smooth, not jerky, and you should be able to easily adjust the tension level to suit your ability. Don't rush through a test run. In fact, you may want to return to the store for a second visit before you invest in a machine.
After you've made the purchase and have your rower set up, it's time to craft your initial workout parameters. The intensity of your workout depends on two factors: the resistance setting; and your stroke rate -- the speed at which you row. If you're a beginner, start with an easy five-minute warm-up, aim for 15 minutes of rowing, and then finish with a five-minute cool-down.
As you progress, gradually increase resistance and/or stroke rate. Note that a slower stroke rate with high resistance may hurt your back, especially if these muscles aren't strong. In fact, if you have a history of low back pain, have a trainer teach you the proper rowing technique to prevent injury.
The industry group American Fitness Professionals and Associates has an online guide to rowing machines that further details the options.