You can use the bed for any exercise you'd do on the floor. Try doing crunches, alternating crunches and knee lifts or leg lifts. The bed is also an excellent place for doing planks -- as long as the bed is big enough for you to fit on it -- and curl-ups, in which you start sitting and then lie back, flexing your back so your shoulders stay off the bed. Sit back up to complete the repetition. During every exercise, keep your abs tight and strong to stabilize yourself on the bed's surface.
If you have a pair of dumbbells, you can lie on your back in bed and do chest presses: Start with the weights straight over your chest; then bend your elbows and lower the weights down and to the side until your elbows just brush the surface of the bed. Press the weights back up to complete the repetition. You can also do chest flys -- swinging the weights out to the side with your arms slightly bent -- and, if there's enough space, turn over and do pushups on the bed. Think "abs tight" to keep your body straight from head to heels, and don't be afraid to do pushups on your fists, wrists straight, if you find the palms-down position to be uncomfortable.
Use your bed and a single dumbbell to do bent-over rows. Stand beside the bed and bend your near knee, placing it on the bed; bend your upper body forward at a 90-degree angle, keeping your back flat, and support yourself with one hand on the bed. Hold a dumbbell in your other hand and let it dangle straight below your shoulder. Pull the dumbbell straight up, keeping your elbow close to your body. You can also do back extensions to work your erector spinae: Lie facedown on the bed, tighten your abs and lift your chest off the bed.
Sets and Repetitions
For chest and back exercises, start with one set of eight to 12 repetitions. Once you can do more than 12 repetitions with good form, use heavier dumbbells or move on to a more difficult variation of the exercise. For core exercises, the American Council on Exercise recommends doing one to three sets of 10 to 25 repetitions.
Stretching and Repetitions
Stretching in bed is a relaxing way to start or end your day. Lie face-up with both knees bent, feet flat on the bed; hug both knees toward your chest to stretch your lower back. From this position, cross one ankle over the other knee and let the knee of the crossed leg wing out to the side to stretch deep in your hips. Then extend one leg at a time straight up, pulling it gently back toward your upper body to stretch your hamstrings. Flex your feet, as if you were pointing your toes toward your forehead, to stretch your calves.