If you opt to use your infant car seat as a carrier, realize that it can be a killer on your wrists, elbow, lower back, and neck if you tote it by the handle or if you string it on your forearm like a handbag. "The greater the horizontal distance from the weight you're carrying to your torso, the more stress on your joints, discs, ligaments, and muscles," says Mary Ellen Modica, a physical therapist at Schwab STEPS Rehabilitation Clinic in Chicago, Ill. "It's equivalent to walking around with three or four full paint cans in one hand--something most people wouldn't do, but yet, they'll carry a car seat that way."

Instead, "Carry the car seat in front of you so that you have both hands on the handle," advises Diane Dalton, orthopedic clinical specialist at Boston University's Sargent College of Health and Rehabilitation, in Boston, Mass. With the weight of the seat and your baby centered and close to your trunk, the force on your body will be reduced, Dalton says. Another option: Leave the infant seat in your car and transfer your baby to a soft infant carrier or a stroller, or use a travel system.

Or simply carry your baby in your arms, and your child will benefit. Infants transported that way use their head, neck, and shoulder muscles and establish stronger trunk stability. "Those upper muscles may develop sooner in babies who aren't carried around in a car seat," says Patrice M. Winter, a physical therapist and consultant in northern Virginia.