We received tremendous feedback from participants in The Wall Street Journal Fitness Challenge, a six-week program developed by Arnie Kander, an NBA sports performance coach. Haven’t signed up yet?

Fitness experts share goal times for holding a plank by age, why the exercise is so helpful for core strength, and some ...

Add Yahoo as a preferred source to see more of our stories on Google. Using proper form while exercising improves performance overall and lowers the risk of knee or back pain. (Getty Images) (vitapix ...