While recently having attended a performance of a famous group of artists of acrobatics, I started to think about training in some general terms, not just specifically in the D/s context. Given those extraordinary control about their body that these acrobats have (and probably inspired by their tightly clad bodies), that flow of thought just occurred to me. Oh and yes, I obviously also had to think of the kind of positions they would be able to have sex in, but that's not the issue that I want to write about right now ;)
So let's first look a bit at the acrobatic artists: They train their bodies to bend into positions that seem impossible. They obtain a feeling for (and control of) balance that is truly amazing.
What will bring them to one of the [world] famous acrobatic companies? They will probably endure hard training starting at a very young age. Many of them will not be doing this entirely voluntarily, but more because their parents/trainers keep on insisting that such valuable talent has to be "made use of", improved, etc. Certainly none or almost none of the artists will be able to sexualize/eroticize that kind of pressure, submission, ...
Looking back to the D/s training, especially in those areas that I'm interested in, I think there's some analogy. It, too, is about achieving higher control about certain aspects of the body. Being able to control the gag reflex in the case of deep throating. Being able to sustain quite unnatural position of the feet in case of high heel training. Being able to handle an increased breathing rhythm and constant pressure to the body, maybe even reshaping the torso in the case of corset training.Other people also like to engage in anal training, being able to stretch the sphincter to a desired above-average level. Or, lets look at posture training, where the trainee has to learn how to walk and manage to keep a book on top of the head, without making it fall.
So in both cases we're dealing with the fundamental strive to alter/enhance some physical aspect of the body. I think in both cases (to a varying degree) the main motivation can be described as: To be able to be better than other people, to be different from them, to be special. To please others (and oneself) by demonstrating the abilities of the enhanced body. To be respected/recognised by the enhanced abilities. I think it's just logical that training of something for the purpose of sexual enhancement of the body can also in response become sexually rewarding - whereas training for something asexual, will just be regularly rewarding.
The closest connection between training acrobats and sex related training is probably visible in the case of certain contortion fetishists. Here the mere act of being able to bend the body is what is fetishised. I can hardly imagine that for a couple where e.g. he is a contortion fetishist and she is a contortionist, she wouldn't be more motivated to proceed/advance with the contortion training, because she notices his sexual reaction. This doesn't even mean that we are talking about a D/s relationship at all. Obviously a combination was possible (and isn't it an extremely interesting one?).