Gyms are crowded with cardio machines comprised of rolling belts, whirling petals, gliding footplates, and handlebars. Each one promises a great cardio workout, intense muscle toning, exceptional calorie expenditure, and maximum effect with varying degrees of impact.  Dozens of programmable training options dizzy the mind before you even hop on a machine.  Which one is best?  We looked at four popular cardio machines: the elliptical trainer, treadmill, stair-climber and stationary bike to find out, which one offers the best workout.

Mike Ceja, certified sports therapist and personal trainer at Lloyd Athletic Club in Portland, OR says, "The 'best' cardio machine depends on your fitness level, goals, and what your body allows.  Each machine offers something different. If you're going for best for cardio training, calorie burning, and total-body toning, it's the elliptical trainer.  If you want a machine that best simulates the body's natural stride and exercise pattern, that's the treadmill because people were made to walk. Want a machine that works the body to its maximum capacity? That's a stair-climber.  Recumbent and stationary bikes provide the lightest impact and are best for people with knee problems, injuries or who aren't ready for upright machines like a treadmill or elliptical.  The best machine is the one that's best for the individual."

Elliptical trainers. They provide all the cardiovascular benefits of walking or running but without the bone and joint-jarring impact. Elliptical trainers can provide a total body workout, especially with proper core alignment and handle-bar/ski pole use.  Ramp up the resistance and incline to increase the amount of effort and calories you expend. Program it for "weight loss," "fat burning" or "interval training" and this machine may be the best one for high-performance cardiovascular exercise and overall muscle and core toning.  Average number of calories burned in an hour (for a 150 pound woman)? 770. 

Treadmill. A study at the Dublin City University picked the treadmill for "best fat burner." The number of calories you expend depends on how fast you walk or run and how much incline you use. Ceja likes treadmills for exercise beginners because they make people move more than some machines, even at a slow pace. "Treadmills can only go so fast, but that can be limiting for advanced athletes." Walking for 60 minutes at 4 miles/mile burns on average 280 calories. Running an 8-minute mile for 60 minutes burns about 880.

Stair climbers. The faster you go and the more resistance you use, the harder you'll work. Stair climbers provide a challenging cardio workout but Ceja says most people can't sustain a long training session on a stair climber. "When I set a stair-climbing machine to perform at maximum capacity, I'm exhausted within a few minutes." Ceja says stair climbers are best for advanced athletes looking to push themselves or for cross-training. Stair-climbers can be tough on knees, ligaments and joints. A 60-minute workout burns about 500 calories.

Stationary bikes. They provide the best cardio workout you can get sitting down. They're great for both serious athletes and people that need an easier-on-the-body fitness program with minimal impact on joints and bones. Peddling at a moderate pace for an hour burns about 490 calories.  Kick it up in a high-intensity spinning class and you'll burn about 800.