RUNNING-SHOE MANUFACTURERS peek at each other's homework all the time. Need proof? Compare the eight kicks on the pages that followthis year's best in showand you'll see that they share some notable breakthroughs. More shoemakers are using mesh in the uppers, which helps your feet breathe better, even during sweltering summer workouts. You'll also find plenty of fusion welding, a process new to the athletic footwear market that involves bonding materials with heat and glue (rather than stitching) to increase durability without adding weight. And many designers are lightening up, going easier on the shock-absorbing air/gel/fluid cushions under the heelsgood stuff that can weigh down shoes when overused. These and other innovations have been rolled out in a range of models, so whether you need a swift racer for your next 10K or beefed-up trainers for pre-marathon regimens, you'll have no trouble finding a pair to kick your style.