Back to school is just ahead for New Jersey kids. But before sending them out the door, parents should check their backpacks.

Is it too heavy? Are they carrying it correctly? Not doing so could cause injuries parents and children may not know about.

Backpack-related injuries force nearly 5,000 children to the emergency room each year.

Jeannie Baer, a New Jersey chiropractor and member of the American Chiropractic Association, says a child's backpack should be no more than 10 percent of a child's total body weight. This is what she calls the green zone.

But she says a significant number of kids ages 8-12 run around with backpacks weighing more like 15 and 18 percent of their body weight. This is the yellow zone.

The red zone means the backpack weighs 20 percent or more of your body weight and that's where you're going to suffer injuries.

Baer says the most common injuries include muscular pains and strains and repetitive stress injuries associated with the day-to-day carrying around of the backpacks. Occasionally, a more serious injury occurs if a child has a compass, protractor, pencil or pen that protrudes out of the backpack, puncturing and injuring a child.

Kids who carry extremely heavy backpacks can also suffer from neck, upper and lower back, shoulder pains, postural changes and muscular tightness and tension.

She says these backpack injuries and pains can continue to a person's later years as well.

"I do see older kids or college age kids and sometimes folks in their late 20s and early 30s who have some postural issues and postural changes that have occurred because of their backpack carrying," says Baer.

But the good news is that there are ways to reduce the strain and pain of a backpack on your body. Make sure you're carrying some of the books in front and make sure you're not carrying items that you don't really need in your backpack to get it out of the yellow zone and into the green zone.

You should also be wearing the backpack on both shoulders. That is key. Slinging it over one shoulder is going to cause tremendous pain on your neck, shoulder, back and muscles.

So when shopping for a backpack as part of your child's back-to-school necessities, Baer says "primarily your first goal is to get a two-strap backpack. It should have two straps so it can be worn on both shoulders. I cannot emphasize that enough."

Baer says the shoulder straps need to be padded. The padding is needed to distribute weight over some of the bumpy parts of the child's bones. She adds it's important to look for padding along the backside of the backpack, too.

She also stresses that the straps should be adjustable so you can adapt the height that the backpack is hanging from your shoulders and down the back.