We've always known that same-sex bonding is good for the soul. Turns out it's good for your silhouette, too! So grab a few girlfriends and try this quick at-home regimen from Equinox Fitness Club's Stacey Lei Krauss. Start with level one, then after six weeks, challenge yourselves with level two.

WHAT YOU NEED: a group of three or more friends, a stopwatch/timer and one six-pound medicine ball per person (find them at any sporting-goods store).

1. CARDIO

6 minutes total

LEVEL 1: Holding your medicine balls at waist level, march in place.

LEVEL 2: Holding your medicine balls overhead, jog forward five steps, then back five steps; repeat.

2. AGILITY DRILLS

6 minutes total

Do each of the following drills for one minute apiece:

1. Ball toss-up:

LEVEL 1: Throw the medicine balls just above your heads; catch; repeat.

LEVEL 2: Squat, then throw the medicine balls as high as you can, pushing through your heels and standing as you throw; return to a squat position to catch; repeat.

2. Push-ups:

LEVEL 1: Do on bent knees.

LEVEL 2: Do on toes.

3. Twist squats:

LEVEL 1: Stand with the medicine balls at hip-level, then twist to the right as you squat and touch the ground with the balls. Alternate sides.

LEVEL 2: Rather than touching the ground with the balls, lightly bounce them; stand; then toss the balls above your heads; catch. Alternate sides.

4. Bicycle crunches:

LEVEL 1: Lie on your backs, hands behind your heads. Twist your upper bodies right and left while your legs "pedal" back and forth.

LEVEL 2: As you pedal, lower outstretched legs until they're about an inch above the ground.

5. Side hops:

LEVEL 1: Place medicine balls on the floor and step back and forth over them.

LEVEL 2: Hop back and forth over the balls, keeping your feet together.

6. Balance training:

LEVEL 1: Stand holding the balls at chest level. Lift your right legs (bent at the knees) and tuck feet into your standing legs. Close your eyes.

LEVEL 2: Holding the pose, slowly press the balls overhead; lower; repeat.

3. CARDIO

6-10 minutes total

LEVEL 1: Do these two drills for three minutes each.

1. Jog in place, holding the medicine balls overhead.

2. Shuffle to the right five times, then to the left five times. Alternate for the allotted time.

LEVEL 2: Do the same two drills, but repeat them for five minutes each.

4. PLAY CATCH

6-12 minutes total

Toss a ball:

LEVEL 1: Grab a partner and a ball, and do the following tossing drills for one minute each.

1. Toss ball high and easy.

2. Toss right-handed.

3. Toss left-handed.

4. Toss underhand.

5. Toss hard from chest, with elbows wide.

6. Toss even harder, increasing speed and force.

LEVEL 2: Do each of the six drills above for two minutes apiece.

5. COOL DOWN

6 minutes total

LEVEL 1: March in place for five minutes, then stretch for one. A great core stretch: Stand with legs wide, hands on hips. Now, keeping shoulders back and legs straight, slide right hands down to touch your right knees, hold for one second, then slide up. Alternate sides.

LEVEL 2: Jog in place for four minutes, march for one, then stretch for the last 60 seconds.

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