Some women aren’t comfortable lifting free weights and barbells, but they still need to mix resistance training with cardio to get in optimal shape, says Robin Cortez, the San Diego-based director of team training for Chuze Fitness, which has clubs in California, Colorado and Arizona. An array of machines provide good alternatives for women “who are intimidated by barbells and bumper plates and squat racks,” Cortez says.

Resistance training is any type of exercise that helps increase muscular strength as well as endurance. Muscles are exercised while employing some kind of resistance, which could be free weights, weighted gym equipment, bands and your own body weight. Resistance training is useful to maintain tone and build strength and endurance.

Also, as women age, they naturally lose lean muscle mass which plays a crucial role in the number of calories their bodies burn at rest each day, says Jenny Harkins, a certified group fitness instructor and owner of Treadfit, a fitness brand based in the Chicago area.

"Oftentimes, we hear women say they have put on weight because their metabolism is slowing down as they get older," Harkins says. "What is actually dropping is their basal metabolic rate, most likely from a drop in lean muscle."

The only way to improve your body's efficiency in burning calories is to drop body fat and increase lean muscle mass, which you can do by engaging in strength training. Here are 10 user-friendly gym machines women can use to get in shape:

• Smith Machine.

• Water Rower.

• Glute Machine.

• Hack Squat.

• Total Gym Core Trainer.

• Treadmill.

• Stationary Bike.

• Seated Reverse Fly Machine.

• Assisted Pull-Up Machine.

• FreeMotion Dual Cable Cross.