yard work

Why is it that yardwork takes so much out of us? I decided to be constructive this weekend and do yardwork.
I started working around our fire pit. I raked, gathered branches, burned, picked up glass. This process took about 2 hours or so all the while the dogs are running and playing. Then I moved to a flowerbed by our back door. The flowerbed basically only has aloe vera and roses in it but the weeds had taken over and since it is by the door that we always use I wanted to start there. I set out pulling weeds, using a little hand rake. I pulled and pulled thinking that the weeds were multiplying as I pulled. I finally finished the weeding and then hauled pine mulch to put over the sand to make it look nice and to hopefully keep the weeds from coming back as readily. The finished product looks really nice but man is my back killing me. My arms are sore, the back of my legs are sore, my lower back is sore. I must be getting old, I just can't handle that many hours of yardwork anymore. So today I am home, sleeping, resting and doing absolutely nothing. Unfortunately I have another flowerbed in the front yard I want to do next weekend. I will take it slower and gradual so I don't wear myself out this time. My body just can't take the pain!