Their workouts used to take them miles apart. He'd jog left at the mailbox on a Saturday morning, she'd walk right. They had both been looking for a fun social activity they could do together to increase their circle of friends and to put a new spark into their marriage. Then they tried something one weekend on a friend's advice. They skipped their Saturday-morning workouts and went dancing that evening instead. And guess what? They've been burning calories cheek to cheek every Saturday night ever since. This tale is a composite of stories we hear all the time: Moving feet draw people closer."It's the ultimate togetherness workout," says Phil Martin, a lecturer and dance instructor at California State University, Long Beach. "You move in a physical harmony that works toward an emotional harmony. You also tend to bring back a lot of fond memories. The dance floor can be a great place to give a tiring relationship a second wind." Not just the heartstrings get pulled by the likes of a good fox-trot, however: the heart itself gets a loving tug. "Studies show that steps such as the Cha-Cha, Polka, Samba, Viennese waltz and East and West Coast swing easily can raise the average person's heart rate enough to achieve an aerobic-conditioning effect, Martin says. "You tend not to realize it, though, because you're having too much fun.""Surveys show that fewer than 15 percent of Americans have been successful at sticking to the kind of three-workout-a-week schedule currently recommended for good cardiovascular health, says Bryant A. Stamford, Ph.D., director of the health promotion and wellness center at the University of Louisville and co-author of Fitness Without Exercise (Warner Books, 1990).