Not all that long ago, people owned one generic pair of gym shoes, which they used for all sports and activities. Those days are long gone. Athletic footwear is a $16 billion business in the United States today. That figure is expected to grow rapidly over the next few years, as Americans buy multiple pairs of athletic shoes designed for different activities. But is it really necessary to have a closetful of sneakers, or is this all just marketing hype?Not all that long ago, people owned one generic pair of gym shoes, which they used for all sports and activities. Those days are long gone. Athletic footwear is a $16 billion business in the United States today. That figure is expected to grow rapidly over the next few years, as Americans buy multiple pairs of athletic shoes designed for different activities. But is it really necessary to have a closetful of sneakers, or is this all just marketing hype?