The postures and sequences taught in contemporary classes have a traceable history. It is shorter than usually assumed and involves several sources that were combined deliberately.
Hatha texts describe fewer postures than expected
Medieval hatha yoga manuals describe a modest number of positions, many of them seated, alongside extensive material on breath, locks, cleansing practices and internal work.
The postures serve those other practices rather than forming a system of their own, and the texts give them correspondingly limited space.
Standing postures, which occupy much of a modern class, are largely absent from this literature.
Physical culture supplied new material
The late nineteenth and early twentieth centuries saw wide international interest in gymnastics, wrestling training, calisthenics and systems of exercise built around sequences and drills.
These methods circulated in India as elsewhere, taught in schools and gymnasia and associated with health, discipline and national revival.
Teachers developing yoga instruction in that period worked in an environment where such training was familiar, and several had direct experience of it.
The synthesis happened in identifiable settings
Influential teaching in the early twentieth century combined postural work with breathing, sequencing and a philosophical framework drawn from classical texts.
Instruction there was often organised into flowing sequences and adapted to individual students, and several teachers who later taught internationally trained in this context.
Their students went on to develop distinct systems, which accounts for much of the variety among widely practised styles today.
International transmission changed emphasis again
As practice spread internationally, postural work was foregrounded and other elements were reduced, since posture translated most readily across languages and settings.
Class formats, studio economics and fitness contexts pushed further in that direction, producing sessions defined almost entirely by physical sequences.
Cleansing practices, extended breath work and the ethical framework survived mainly in teacher training and in lineages that retained them deliberately.
Knowing the history clarifies current claims
Describing a modern sequence as thousands of years old overstates the continuity, while calling it merely gymnastics understates the classical material it carries.
Scholarly work on this history is well developed and draws on manuscripts, photographs, training manuals and the recollections of the teachers involved.
The accurate description is of a living tradition that has repeatedly absorbed new material, which is how most durable practices have persisted.