The following series of exercises from classical pilates provides a quick core workout:

Hundred

Rollup

Single Leg Circles

Rolling Like a Ball

Single Leg Stretch

Double Leg Stretch

Scissors

Two-Leg Lower Lift

Criss-Cross (Bicycle)

Spine Stretch Forward

Corkscrew

Saw

Dart

Rest Pose

Single Leg Kick

Side Kicks Front and Back

Side Kicks Up and Down

Small Leg Circles

Inside Leg Lifts

Inside Leg Circles

Teaser

Seal

Pushups

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