Whether Buddhist in origin or not, the kata also incorporates Taoist 'Immortality' ritual aspects and emphasizes forced breathing in conjunction with a distinctive pelvic movement whereby the pelvic bone is retracted on the in breath and pushed forward on the out breath.
The Goju ryu version of the kata performed by Master Morio Higaonna emphasizes dynamic tension and this is tested - sometimes severely - by heavy slapping. This may not be healthy (and in my opinion, it isn't) as the body is simultaneously starving the muscles of oxygen (through the tension) while also depriving the body as a while of oxygen (through the slowed, forced breathing). Author Mark Bishop draws attention to the fact that several high ranking Okinawan karateka have died at relatively young ages (and consider that Okinawan people currently have the highest average life expectancy anywhere in the world) of complications relating to their heart condition. He himself eventually quit the practice of the kata for this reason and I have also read that this practice is rejected by Chinese martial artists who execute their similar form without the forced breathing and dynamic tension. This kata is seen to represent the 'hard' aspect of Goju, with Tensho being the softer side.
Master Morio Higaonna performing Sanchin