School starts next week in Boise, and kids will be cramming iPods, notebooks, Kindles, phones, a change of shoes, snacks, and maybe even a book into those backpacks.

How heavy is too heavy?  If the backpack weighs more than a certain amount, it can knock kids off balance and lead to back problems later on.  Here's the magic number.

Backpacks shouldn't weigh any more than ten percent of your kiddo's body weight, according to the experts.  So if your son weighs 60 pounds, his backpack shouldn't be any heavier than 6 pounds.  If he's an offensive lineman on the high school football team, his backpack can hold a phones and iPads and a handful of dumbells and he'll be okay.  It's all relative.

Constantly looking down at smart screens can cause enough problems with posture, so kids don't need heavy backpacks messing with their backs and shoulders.

Here's the great news in all of this.  If you're a college student headed to Boise State this fall, this provides the incentive you need to go ahead and gain the freshman 15!  More weight equals more backpack carrying capacity.  So eat the pizza at 1am and own the power.