Par4QC The force of the weight is what is pulling on those tendons
Seems to be the case, when I went from 125gr to 105gr steel after a torn shoulder tendon, the fatique and sourness in that shoulder after a round of golf disappeared. It took me whole season however to get used to that weight and find the sweet spot again on the clubface. So even when I was hitting more off center with the lighter shaft and thus inducing more vibration, it was less stressfull.