(FORTUNE Magazine) – A 97-POUND WEAKLING on the TV screen peers into a mirror, wishing, no doubt, that he was endowed with Schwarzenegger-size muscles. Suddenly, a disembodied voice tells the skinny kid that he does not have to be such a wimp. The scene is not from one of those commercials that clutter late-night TV movies. It is the opening of a 22-minute videocassette that Soloflex Inc. mails to prospective buyers of its $850 exercise machine. Soloflex is one of many companies that have turned to videocassettes to sell everything from sophisticated cameras to package tours. Says Ronald Kaatz, media concepts director for J. Walter Thompson USA in Chicago: ''These advertisers are at the starting line in a tremendous race.'' The explosive growth of videocassette recorders has transformed them into an attractive advertising appliance. Companies like Soloflex and Air France send ''video brochures'' to prospective iron pumpers and jet setters who request them by calling toll-free numbers in advertisements. Soloflex lets prospects keep the tapes. Air France asks viewers to return its 15-minute travelogues within ten days or pay $29.95. Soloflex spent $150,000 to produce its tape; the copies cost $6.50 to make and mail. Jerry Wilson, owner of the private Oregon company, says nearly half of those who receive the video buy a machine, vs. only 10% who peruse printed brochures. Hollywood studios have been putting trailers for other films on videocassette movies for several years. Coca-Cola is testing a new idea. It has put a soft- drink commercial at the start of the foreign cassette version of Ghostbusters, a hit movie produced by Columbia Pictures, a Coke subsidiary. Other advertisers produce special-interest cassettes to sell in video stores. Glenmore Distilleries Co. made the Mr. Boston Official Video Bartender's Guide, a $14.95 cassette distributed by a subsidiary of Lorimar Telepictures. The tape features bartenders at six watering holes around the U.S. demonstrating how to create exotic cocktails. Mr. Boston liquors and other Glenmore brands figure prominently in the lessons. Diane Cline, president of DMC Video Communications in Rowayton, Connecticut, produced a 30-minute video for Cuisinart on how to use a food processor. The $19.95 tape sells alongside Cuisinart machines in department stores. Cuisinart claims it has sold 40,000 copies since late last year and says the tape is boosting processor sales. Esquire Magazine Group has added another twist to video marketing. It sells a series of $14.95 and $29.95 video guides on subjects such as how to dress for success. The tapes promote the Esquire name and also tout the products of advertisers, including Vidal Sassoon and Neiman-Marcus. Sassoon paid $20,000 to be on one tape. That is nearly as much as it costs to reach a much larger audience with a four-color ad in Esquire magazine, but some advertisers figure the cassette crowd is worth it.