In high school P.E., we did jumping jacks, “burpees,” pushups, pull-ups, sit-ups, toe-touchers, trunk-twisters and something called chain breakers. You put your fists together, jerk them halfway apart ...

"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links." The chain is one of the most important parts of any bike. After all, without a chain, a bike is just a ...