12K run commute home. Still amazingly warm out. Finally pulled the trigger on buying a running specific backpack to carry my work stuff and clothes back home with me, and it made a huge difference in the pain I was experiencing around my right shoulder and neck when running any length of time. Having that additonal waist strap took the pressure and bounce off the nerve bundle that was bothering me, and it was just the right shoulder area. The left was fine. Bonus that there is a blinky light built into the backpack for extra safety in these long night days.