It's not all about planks and crunches—there are plenty of lower-intensity moves that will engage your muscles, raise your heart rate, and improve your posture. Like the routine below, which doesn't even require you to stand up. Do this circuit 3 times in a row, spending 30 seconds on each move. Be sure to use a sturdy chair that doesn't have wheels.
Don't let the name fool you: There's no jumping here since you're fully supported by your chair. This move serves as a great warm-up that's easy on your joints. Start sitting with legs glued together in front and arms by sides. In one swift movement, reach legs and arms out to a star position, then quickly bring back in. Be sure not to slouch, and use your core to keep your torso upright the whole time.
Sit up at the very front of the chair, with your entire body facing one side. Then lift your arms out in front and bend 1 leg up and in towards your chest and hold. If this is challenging enough for core and balance, stay here 15 seconds, then switch sides. If you're up for a bigger challenge, elevate both legs while squeezing knees, ankles, and big toes together and hold, sitting up tall on sit bones. If you can, straighten your legs.
Sit facing forward, and extend 1 leg out long to the side of the chair. Bend the other leg and extend it out to the side as well. Bring your hands behind your head and lean toward your bent leg. Reaching longer leg away from your body, use obliques to control side bend over and back up, squeezing sides. Avoid bending so far over that feet come off the ground.
Sit sideways on a chair with both feet firmly planted on floor. Wrap your hands over your core and sit up as tall as you can. Take a nice big inhale and on the exhale roll back until your spine is in the shape of a "C." Make sure your feet stay planted on the floor and you only feel the work in your abs—avoid using your back. Keep your collarbones open, shoulders back and down, and your neck nice and long.