yes...ive actually been designing a cardio piece (diagram phase only)
just make sure that you at least try to have a patent pending if you decide to submit it to equipment companies. over the years there have been numerous lawsuits because of "stolen" designs. if you can mock up a prototype...thats great, but dont even consider trying to make anything for production.
every year there are one or two booths at the major fitness conventions that have a "new" revolutionary leg extension...or some shit like that. waste of time and $$$$. get an idea, patent it, get a lawyer and submit to major labels. if its a no-go, submit to the smaller guys....