I use a Gerbing (Cabelas) 7v vest and/or 7v waist band in cold weather. The pads inside the vest are in the core area and the vest needs to be worn tight with only a light base layer top underneath to really feel the heat on your back and kidney area. I wear the waist band the most because I get better contact in my lower back. I'm not sure it would help your tricep area. The chemical warmer pads like Hot Hands might work better if taped or banded to the upper arm. I think they might even make them in a larger size that are supposed to adhere to your body.
The older I get, the stronger gravity becomes.