At the end of the day, when you're cranky and brimming with excess corporate aggression, you could haul your sedentary self to the gym and blow it all out on the machines. Or you could hop into a boat and skim around Lake Merritt, watching brown pelicans dive for their dinner and gondoliers slowly propel their shapely crafts across the water. Rowing (with one oar) or sculling (with two oars) in a sliding-seat boat uses virtually every muscle in your body and pumps your heart efficiently. For those now limping along with shinsplints, courtesy of years of jogging, these water sports are nonimpact (at least, until you crash into a pier or a gondolier). And they can be as solitary or as social as you like -- the Lake Merritt Rowing Club has a fleet of singles as well as crew boats. No longer a sport reserved for overgrown Ivy Leaguers, rowing draws all body types and ethnicities. Gay rowers are welcome, too -- they've formed their own group at LMRC, the Bay Blades. The club's sheltered location produces relatively smooth water, although the algae occasionally becomes an oar-trapping obstacle. Another edge LMRC has over most clubs is its regular novice classes -- 10 hours of instruction for $100. After you've learned the basics, you can row with the intermediate crews or become a lone sculler, whichever suits your temperament. The only downside is that once you've tried hauling on an oar, a rowing machine seems like a mighty poor substitute.