Then

there's another problem: kids that weigh as much as a

large sack of flour - and won't sit still.

"If a

child jumps into your arms and you're not expecting it,

your risk for injury is greater because you aren't

thinking about your movements," says rehabilitation

engineer Gerald Wiesman.

With more

people having children in their 30s and 40s, the

likelihood of preexisting "wear and tear" on

the spine also sets the stage for problems. New parents

are especially at risk because they are not conditioned

for the physical rigors, says Helen Horstmann, M.D., an

associate professor of orthopedic surgery.

"More

than lower back pain, parents tend to feel the strain in

the area between their shoulders...The pain comes from

bending over and doing repetitive activities - lifting

and placing the baby in a crib, high chair, or

playpen," says Dr. Horstmann, who has six children

herself.

The fatigue

that goes along with 2 a.m. feedings likewise contributes

to injury. When parents are more tired than usual, their

muscles don't respond the same way.

For both

men and women, age is not nearly as important as fitness,

Mr. Wiesmann emphasizes. "If you stay as fit as you

can, avoid awkward or extreme postures, and hold heavy

weight as close to your body as possible, you can avoid

most problems."