Ah I see, yes that is quite simple.
Any tips for running with a backpack? I often commute by running, but hate running with a bag
I train with a back pack often - it's a rucksack from www.goruck.com
What I've found is key is that you need one that sits high and tight on the back...so it doesn't bounce and kill your shoulders.
Also, depending on the weight used, it's best if you alter your running style to where you "roll" the heel to the front to minimize impact, since running with weight can mess up your joints.