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Cardio exercises, like using the stair master, can help build the muscles around your hips and butt.  Incorporating the stair master as a form of cardio can help increase the size of your hips.  Studies have shown that the stair master recruits about 24% of your glutes and hip muscles. Use the stair master 1-2 times a week for at least 30 minutes per session. To make this exercise more challenging and target your hips and butt, lean forward when stepping and do not hold onto the side rails.  This forces your body to use your butt muscles more significantly. Also take large steps - almost as if you were taking two at a time.  This actives a large portion of those muscles. Another cardio machine that can help tone your butt, hips and increase the size of your hips is the elliptical.  It gives you the opportunity to really work those muscles.  The elliptical machine recruits about 36% of your butt and hip muscles.  This is slightly more than the stair master. Use the elliptical for at least 30 minutes.  However, to get a well rounded workout, try doing 15 minutes of the stair master plus 15 minutes on the elliptical. To help target your hip and butt muscles, really focus on pressing down your foot, heel first.  Also ease your hips backwards a bit, so that your butt is popping out a bit.  This position helps specifically target those muscles. Running is a great cardio exercise.  In general, it's a great way to target your butt and hips.  However, using a treadmill allows you to use the incline function making this machine a great way to increase your hip size.  Walking or jogging on the treadmill recruits the highest amount of your hip and butt muscles - almost 50%. Walk or jog on the treadmill for at least 30 minutes.  Again, doing a combination of multiple cardio exercises can help work your butt and hips in different ways giving a better overall workout. To really target those hips, increase the incline on your treadmill.  This places more stress on your glutes and hips and also give your bottom half more definition. Another option is to walk sideways on a treadmill. Set the treadmill on an incline and start at a slow pace. Cross your legs over one another to walk sideways. This will give your hips the tension they need to induce muscle growth. If you want to burn a lot of calories while toning your hips, consider taking a spin class.  It's a great exercise to help strengthen and tone your hips, butt and thighs.  Spin classes recruit many of the muscles around your hip and butt.  The up and down positioning and varying resistances help make this a great exercise to increase your hip size. To help really target those hips, sit farther back on the bike seat and really focus on pushing down hard on those pedals.  You may even want to increase the resistance. If you're in a standing position on your bike, really stick your butt out far behind you.  This position is another one that will require you to stabilize your body with your butt and hip muscles. Your exercise plan should include at least one day of rest per week, to prevent plateaus and give your body time to recover. Mix up your workouts and their intensity to keep yourself motivated.

Summary:
Use the stair master. Hop on the elliptical. Walk or jog on the treadmill. Take a spin class. Give yourself time for recovery.