More and more of our experiences come to us through machines, particularly those tiny ones called microchips. As digital technology continues to improve, the distinction between data and experience will blur further. But, as media analyst Jerry Mander wrote in his 1978 book, Four Arguments for the Elimination of Television, if people actually believe that watching a public-television documentary on the rainforest is equivalent to being in the rainforest, then the environment is in even deeper trouble than we thought.

The contrast between direct and machine-processed experience shows up even at my health club. There, I work out on a rowing machine that measures my "distance rowed" in meters via an electronic monitor—even though the machine and I are not moving an inch. Nearby, others jog on treadmills set to mimic the rolling hills of the Boston marathon, making only numerical progress. And the cross-country ski machine spews out alpine statistics without a snowflake in sight.

Because I have sculled for years on actual rivers, in actual boats, rowing indoors offers a comparison with "the real thing." Serious outdoor rowers do train for endless hours on rowing machines. There is even the World Indoor Rowing Championships, which draws 1,700 athletes to Boston each winter, where they knock themselves out on the machines while going nowhere. It does have a slightly demented aspect. "This is such a crazy event," a competitor once blurted out to me. "Compared with this, arm-wrestling is an intelligent, sensible activity."

Rowers worldwide train on the Concept-II ergometer ("erg"), a machine that nicely simulates the rowing motion: Pulling a handle attached to a bicycle chain spins a flywheel whose fins drag against air resistance. Because air, like water, is a fluid, accelerating this flywheel feels somewhat like pulling an oar through water. And erg performances can correlate with outdoor results. For example, the 1998 men's world champion in single sculling, Rob Waddell of New Zealand, was also the 1998 world rowing-machine champion.

In fact, the machines have certain advantages over the real thing. River frozen? No problem. Snow, rain, high winds, dark of night? Irrelevant: My workout happens indoors at my club. And ergs are convenient. To row my single scull, I must get to the boathouse, carry my oars and shell down to the dock, fasten the oars in the oarlocks, shove off, row my workout, return to the dock, remove the oars, lift the boat out of the water, dry off its hull, and then stow the oars and shell. With the ergometer, I simply go to the club, jump on the erg, row, and get off. An hour on the machine consumes far less real time than an hour in the boat.

The erg also has something boats generally lack: a speedometer. Training in a single scull, I have only an approximate idea of how far I have rowed or how fast I am going. But the machine's electronic performance monitor spews out exact measurements. On every stroke, a microprocessor converts the flywheel's acceleration into an equivalent distance "rowed" in meters. The monitor also reads out stroke rate per minute, time elapsed, 500-meter split times—if you wish, even caloric output. Precise computation of distances rowed allows indoor races like the 2,000-meter sprints at the World Indoor Rowing Championships, where Mr. Waddell set a world record of 5:39.5 last year.

That record time has real significance in the rowing world, because it rests on reliable, replicable measurements—in other words, on data from a machine. Outdoor times are less meaningful. Although rowers enjoy talking about their times over given distances and course records at certain regattas, everyone takes these numbers with a grain of salt, because wind, weather, current, and a host of other factors invariably influence the times recorded.

Still, the nature of floating bodies makes rowing a racing shell a finer, more complex art—and, consequently, a far richer experience—than rowing an ergometer. On the water I am afloat in a thin, light, very unstable boat, and balancing that boat—getting the shell to "set up"—is essential to effective performance. Balance is irrelevant indoors, because the machine sits on solid ground. Furthermore, in a boat I must carefully control my motion on the sliding seat that moves fore and aft: Hurtling my mass toward the stern will generate momentum that counteracts forward progress. The ergometer, too, has a sliding seat, but, there, the only thing I am moving is digits on a monitor, so I can roar up the slide with abandon.

Size and strength are advantageous in shells, up to a point: While I want to apply maximum force to the oar, my body weight also represents most of the load in the boat and can become ballast. In contrast, rowing machines exact no penalty for bulk. One year, a 250-pound former pro football player who had never gripped an oar made the finals at the rowing-machine championships: He was simply a big, strong guy in excellent shape. On the ergometers, behemoths typically outperform smaller rowers, who have counterattacked with a T-shirt motto seen at rowing-machine events: "Put an erg on the water and it sinks."

The most important difference between boats and machines may, in fact, be psychological. The exact readouts of an erg's performance monitor are both a blessing and a curse. True, the numbers provide a useful benchmark, a way to objectively assess myself and measure progress. But there is such a thing as too much data. The satanic electronic display gives out ruthlessly accurate information on every single stroke: There is, unfortunately, no way to fool myself. If my last stroke was even a tenth of a second off my targeted pace, I learn about it instantly. This can be discouraging, even misleading. Digital data can come to dominate my awareness. Glued to the screen, captivated by its "information," I may miss what is happening in my own body, mind, and surroundings.

On the water, we cannot afford so narrow a focus. We must pay attention to wind, water, current, other boats, bridge abutments, bends in the river. Happily, rowing machines offer a predictable, controlled, man-made environment in which to row without such distractions. Boats teach us something different: how to navigate through unstable conditions, how to win amid the vicissitudes of nature and competition—as in real life. Thus, rowing on water teaches us more about thriving on the rivers of commerce, or mastering the fickle currents of human nature, than machines can ever do. The ergometers effectively train mind and body, but to nourish the soul and spirit, we must shove off from the dock, get out on the water, and learn how to win while afloat.