EE HAD LOADED TWO ZINC CANS ONE ON TOP OF THE OTHER ONTO A HANDTRUCK TO MOVE THEM TO THE ZINC FEEDER APPROX. 20 FT AWAY. WHEN HE LEANED THE HANDTRUCK BACK THE CANS STARTED TO FALL FORWARD. HE REACHED OUT AND STOPPED THE CANS FROM FALLING BUT STRAINED HIS BACK IN THE PROCESS.