Got 10 minutes and one kettlebell? Then you’ve got time for girevoy — one of the most effective strength-and-cardio workouts around. A half-dozen fit, determined-looking women, each holding a 53-pound kettlebell in one hand, stand side by side under the watchful eye of a panel of judges. In one powerful motion, each athlete swings her kettlebell from knee to shoulder height, pauses, explosively presses it overhead, and lowers it back to the starting position. Then, without resting or putting the weight down, she does it again. And again. For 10 minutes. Then the men go, holding a 70-pound kettlebell in each hand.