The French didn't only invent the guillotine. They also bequeathed us something even more painful (though that's hard to prove): "Les trois sports", aka the Triathlon. A swimming-cycling-running succession of pure hurt, which Polar's latest RCX5 training computer seeks to measure using an array of sensors and accessories. You can buy it now for $350 in a basic pack, which includes the watch plus the WearLink+ Hybrid, an amphibious chest-strapped heart rate monitor. Alternatively, you can pick up a pricier bundle containing an extra sensor of your choice. The Bike bundle ($390) includes Polar's CS W.I.N.D. speed sensor that installs on a fork and spoke. The Run bun
