I did this workout last night with a friend, and we both thought it was pretty tough! I adapted it from several workouts I saw on FitSugar. Since it doesn't require any weights, it's a really convenient workout to do anywhere. You could do this while traveling, or at home.
I have exercise descriptions below, but please comment if you have any questions or if something is unclear.
Sumo Squat Series
Targets lower glutes and inner thighs
Begin in a wide stance with your legs turned out and your toes pointed outward. With your hands at your chest, perform 10 squats in this position, keeping your hips pulled back, and making sure your bent knees do not move beyond your toes.
Hold your last squat and slowly pulse up and down in a one-inch range 10 times.
Maintain your squat and lift your right heel, and pulse up and down in a one-inch range 10 times before switching sides.
Elbow Plank with Alternating Arm Reach
Targets entire front of the body, and the arm reach forces your abs to work harder to stabilize your torso
Start in an elbow plank. With your abs pulled toward your spine, reach your right arm forward, keeping your torso as still as possible. Bring your elbow back to the mat. This completes one rep.
Repeat on the other side and continue alternating sides for 20 reps total.
Crunchy Frog
Strengthens and tones the entire abdominal wall
Begin sitting, balanced just behind your sit bones, and rock back slightly to lift your feet off the floor. Gently pull your knees to your chest. Exhale, pull your navel to your spine, and lean back slightly as you open your arms to the sides and straighten your legs. Inhale and return to the starting position to complete one rep. Do 20 reps total.
Half Banana
Targets the abs while being gentle on the lower back
Start lying on your back with your arms reaching toward the ceiling. Exhale and roll up toward sitting while lifting your left leg up. Pause at the top and reach for your toes before rolling down slowly back to the mat. This completes one rep. Repeat, lifting the right leg as you roll up toward sitting. Continue alternating sides for a total of 20 reps.
Donkey Kick Pulse Series
Targets the glutes
Begin on all fours and lift your right leg off the floor until your knee is in line with your hip. Flex your foot and squeeze your glute to raise your heel an inch toward the ceiling. Continue these small, concentrated pulses for 15 reps, then continue with your left leg.
Come back to all fours, and lift your right leg off the floor until your knee is in line with your hip. Open your right knee out to the side, keeping your foot flexed, and pulse your leg one inch to the left. You are not trying to lift the knee up, but try to keep it level as it moves behind you. Continue with these small, concentrated pulses for 15 reps, then repeat on the other side.
Pilates Swimming
Targets the back and upper glutes
Lie on your stomach with your arms reaching overhead, pulling your abs away from the floor to protect and lengthen your lower back. Lift your legs, arms, and head off the mat. Keeping your knees straight, lift your entire right leg and left arm a few inches away from the floor. As you lower your right leg and left arm, lift your left leg and right arm away from the mat to complete one rep. Continue alternating sides in a slow controlled manner, keeping your torso stable, for a total of 20 reps.
Squat with Side Leg Lift
Targets glutes and core
Stand with your feet shoulder-width apart, feet parallel. Bend your knees, lowering your hips deeply so your thighs are parallel to the floor, keeping weight back in your heels. Rise back up, straightening the legs completely, and lift the right leg out to the side, squeezing the outer glute. Lower the right leg to complete one rep; repeat the squat again, lifting the left leg as you stand. Do 20 reps, alternating sides.
Down Dog Abs
Targets the whole body - works your upper body while also focusing on the abs. Also provides a nice stretch for the calves.
Start in a Downward Dog pose, actively pushing your weight into your heels while reaching your tailbone to the sky. Lift your left leg up, squeezing the left glute. Exhale and rock your weight forward over your hands, drawing your left knee toward your nose while pulling your abs to your spine to round your back. Inhale and lift your leg up as you push your weight back into your heels. This completes one rep. Do 10 reps, then switch to the other side.
Elbow Side Plank with Twist
Targets obliques and inner thighs
Start in side elbow plank on your right side, with your feet stacked one on top of the other. Place your right hand so your fingers point away from you. Place your left arm behind your head, and inhale to prepare. Exhale, and pull your navel to your spine while rotating your ribcage toward the floor, bringing your left elbow to your right hand. Return to the starting position to complete one rep. Do 10 reps, then switch sides.
Beach Babe Push-Up
Targets chest and triceps, as well as glutes and abs
Begin in plank with your knees on the mat. Extend your right leg straight behind you so it is parallel with the floor. Engage your abs, and keep your left heel in line with your hips by engaging your glutes. With your right leg extended, exhale to bend the elbows, lowering into a push-up. Try to lower your chest until it touches the ground. Inhale to straighten your arms, keeping your leg lifted. This counts as one rep. Do 5 reps on each side.
Twisted Mountain Climber
Targets shoulders, quads and abs
Start in a traditional plank - shoulders over hands and weight on your toes. With your core engaged, twist to bring your right knee forward under your left elbow. Return to your basic plank to complete the rep. Switch legs, bringing left knee forward to the right elbow for your second rep. Do 20 reps, alternating sides.
Split Squat
Targets glutes, hamstrings and core
Stand with your feet shoulder-width apart, feet parallel. Extend your right leg straight behind you, in a reverse lunge. Make sure to prevent your left knee from going past your left toes. Straighten your legs, engage your core for stability, and balance on your left foot, while lifting your right knee up to your chest. Repeat for 10 reps total, then switch sides.
Forearm Plank
Targets entire front of the body
Start in an forearm plank. Keep your abs pulled toward your spine, and your legs in line with your back. Don't hunch your back or stick out your butt. Hold this position for 1 minute.
Butterfly Crunch
Targets the abs
Lie on your back with your knees open and the soles of your feet together (in a butterfly position). Lengthen your arms overhead so they are resting on the floor. Exhale and bring your hands and knees toward each other performing a full-body crunch. Your shoulder blades should be off the mat as you perform a small reverse crunch, lifting your pelvis a bit off the mat. Hold the position for a few seconds, and really feel your abs squeezing. Slowly lower your arms and feet back to starting position to complete one rep. Do 15 reps to complete a set.
Marching Bridge
Targets the back and glutes
Lie on your back with your hands by your side, with your heels about 12 inches from your pelvis. Press your heels into the floor to come into a bridge position with a neutral spine. Press your right heel into the floor, and keeping your knee bent, raise your left leg until your hip is at 90 degrees. Lower your left leg down, pressing through your glutes so your pelvis doesn't lower to the floor along with the leg. This completes one rep; switch sides and lift your right leg for your second rep. Do 20 reps, alternating legs.
Alternating Side Lunges
Targets the glutes and inner thighs
Start with your feet directly under your hips. Step your right foot wide to the side, coming into a lunge with your left fingers touching your right foot. Your right knee shouldn't go beyond your right toes. Keep your chest lifted and your weight in your heels. Push into your right foot to return to standing, then lunge sideways to the left to complete one rep.
Bicycle Crunches
Targets abs and obliques
Lie flat on the floor with your lower back pressed to the ground (pull your abs down to also target your deep abs). Interlace your fingers, and put your hands behind your head. Bring your knees in toward your chest, and lift your shoulder blades off the ground. Straighten your right leg out to about a 45-degree angle to the ground while turning your upper body to the left, bringing your right elbow toward the left knee. Make sure your rib cage is moving and not just your elbows. Now switch sides, and do the same motion on the other side to complete one rep (and to create the "pedaling" motion).