Car buffer style, I'm a fan -
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Also if you can find one on the cheap, the Thumper equine massager -
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That was the best messager I've ever used.
Some creative tools here, esp that Black & Decker, LOL
Sometimes I use a bathing brush, which works pretty flexible and effective. Scrubbing your back or hammies isn't a problem, as long as it has a long handle.