In Fred Wesley's book, he describes the ups and downs of playing in James Brown's band. Some of Wesley's least favorite times would be when Brown called for a rehearsal just so he could have an opportunity to mess around on the keyboard. The rhythm section would be forced to come up with a groove, upon Brown's approval, the horns would have to riff, and Brown would then attempt to play the Hammond organ. These rehearsals could last for hours, sometimes after shows or in the recording studio. "My Brother," I believe, is a product of this type of rehearsal.
If it were not for Fred Wesley's trombone solo on "My Brother," this track would probably have been thrown away, but instead it ended up being one of The J.B.'s greatest hits. The groove is established and then followed by a less than extraordinary organ solo. After two minutes into the jam, funky Fred Wesley is called upon to step up to the microphone and attempt to redeem this recording.
When put into this fight-or-flight situation, Fred Wesley is forced to rely on survival techniques and turns on his machine. He churns out 4-bar phrases quicker than an assembly line (and his riffs only come in Black). One can argue that Wesley recycles certain riffs throughout the solo, but given the situation in which this may have been recorded, many other trombonists simply would not have been able to produce. These riffs and rhythms are the core of who Fred Wesley is, what he breaths and speaks.
The machine-like rhythms of Wesley's playing require great attention to the technique. Once again, air support is biggest factor to replicate his rapid-fire riffs. A player like Trombone Shorty uses air support to extend his playing range, while Fred Wesley uses air support to create his rhythmic assault.
Think of your air support as the stream of water that comes out of a sink faucet. Your tongue acts as your fingers would when you swipe them through the stream of water, they interrupt the flow, but the water pressure is too great that the stream is never broken. To achieve this effect, your tongue and throat muscles must remain relaxed to allow the air stream to continuously flow. Only then can you go play in the stream.
Recommended Reading: Hit Me, Fred: Recollections of a Sideman by Fred Wesley Jr. Published by Duke University Press.