Ann Chisholm , owner and coach at Tropos Fitness Club in Victoria, British Columbia, stands before a crowd of about 20 women huddling in a circle under an outdoor tent, eager to learn about strength training despite the rainy weather.

“What are three common weaknesses in endurance athletes I see in the gym?” she asks them.

The group shouts out guesses. The first two are easy. Glutes ! Adductors ! —Chisholm agrees.

What’s the third one? Hip flexors ? They’re up there, but there is something more important, Chisholm says.

This is the last session on the last day of FeistyFest , a three-day movement and educational festival for women held in September in Breinigsville, Pennsylvania, and none of the previous groups guessed the third one correctly, Chisholm says, before revealing the answer: “Power explosiveness!”

You can think of your explosive power as those first couple of seconds of your movement, the initial burst, Chisholm says.…