Weighty Proposition: America becomes a nation of iron-pumpers.

If it wasn’t so heavy to ship, the dumbbell could well become the promotion business’s next big premium item. Working out with free weights is now the No. 1 fitness activity among Americans, with 41.3 million having pumped iron at least once in 1998, according to the Sporting Goods Manufacturers Association, North Palm Beach, FL.

If one factors in exercisers using fitness machines, weightlifters outnumbered the 55 million people who went fishing last year – an unprecedented lapping of what has long been America’s top recreational pursuit.

And if you’re unwilling to pay the freight for a dumbbell mail-in offer, consider a tie-in with a health club chain. Some 29.5 million Americans held club memberships in ’98, up from 28.3 million the previous year and 70 percent more than in 1987.

So what’s the deal? Are guys madly toning up their pecs to impress the ladies? Au contraire. It’s the women who are sending the numbers through the roof. They accounted for 45 percent of free-weight users in ’98, a total of some 18.6 million people. When American Sports Data, Hartsdale, NY, first conducted the fitness study for SGMA in 1987, only 22.7 million Americans pumped free weights, less than a third of them women.

SGMA pegs weight training’s growing popularity to scientific advances in sports training methods, the growth of personal training, new research showing the benefits of resistance exercise, and encouragement by the media for people to lose weight.