Sohee Lee, a trainer at New York City’s Peak Performance fitness center, reaches for a pair of dumbbells when she only has 10 minutes to spare. “Most women can handle 10 to 15 pounds in each hand,” she says. Hold them at your shoulders and do 7 squat presses—it should take you between 20 and 40 seconds. Then take the rest of that minute to rest and recover. Then switch to plank jacks: Start in plank position and jump your legs out wide, then back in—like you’re doing a horizontal jumping jack with your legs. Again, do seven reps, and spend the remainder of that minute resting. Repeat the sequence 10 times.