Despite this H20 resistance, the Flex won't track your butterfly strokes (or doggie paddles), but it will keep count of your steps, calories burned, sleep and distance walked.

ENGADGET

Strength training can involve a number of approaches including using free weights, such as dumbbells or barbells, resistance or elastic bands that allow you to flex using your arms and legs, as well as ankle weights or vests and other special exercises that use your body weight to simulate resistance against gravity.

FORBES: Why Strength Training May Help You Live Longer