The history of yoga is contested, genuinely interesting, and considerably shorter in its current form than most classes imply.
The textual tradition
Early foundational texts describe a system concerned overwhelmingly with mental discipline and philosophical goals.
Physical postures appear in them barely at all. Where posture is mentioned, it generally refers to a stable seated position for extended meditation.
The eight-limbed framework that classes frequently reference places posture as one component among ethical restraints, observances, breath regulation, sense withdrawal, concentration, meditation and absorption.
Which means the physical practice was originally a small part of a much larger system with different aims.
The medieval developments
Texts from a later period describe more elaborate physical and breath practices, associated with traditions concerned with the body as a vehicle for transformation.
These include a modest number of postures, most of them seated or supine, and considerable attention to breath and internal techniques.
Still nothing resembling a modern flowing sequence.
What happened in the twentieth century
This is the part that surprises people.
Scholarship on the period identifies substantial influence from European physical culture — gymnastics, callisthenics and military training systems that were widely taught in India during the colonial period.
A number of standing postures now considered classical do not appear in any earlier textual source and closely resemble movements from those systems.
The teachers who developed the modern physical practice were working in a context of Indian physical culture revival, nationalism and engagement with western fitness.
Which does not make the result inauthentic. It makes it a twentieth century synthesis rather than an ancient transmission, and those are different claims.
Why this is contested
The scholarship has been criticised, sometimes on academic grounds and sometimes on the basis that it diminishes an Indian tradition by attributing parts to European influence.
The counterargument is that synthesis and adaptation are what living traditions do, and that a tradition being recent does not make it less valuable.
Both positions are held by serious people and I do not think the question is settled.
The appropriation question
Worth addressing directly since it is raised constantly and rarely usefully.
The practice was actively exported by Indian teachers who travelled and taught deliberately, which complicates any simple framing.
The reasonable criticisms concern the stripping of philosophical and ethical content, the use of decorative religious imagery without engagement, and the commercial structure that has grown around it.
Which are specific and addressable, unlike a general claim that the practice should not have travelled.
What it means for a class
A modern class is a physical practice with roots in several traditions, taught in a format developed relatively recently.
That is a perfectly good thing to be. It is stretching, strengthening, breathing and attention, and those have value.
The claims that go beyond that — about ancient origin, about specific physiological effects, about spiritual attainment — are separate and deserve separate scrutiny.
The physical caution
Injury in yoga is real and underdiscussed, concentrated in shoulders, knees, hamstrings and the lower back.
Deep backbends, forced hip openings and weight-bearing on the shoulders are where most reported injuries occur.
A teacher who adjusts students physically without asking, or who encourages pushing through pain, is a reason to find a different class.
Anyone with an existing injury or condition should speak to a physiotherapist or doctor about what is appropriate before starting, rather than relying on a class to accommodate it.
The styles and where they came from
Worth mapping, since the names mean specific things.
Several major modern styles trace to a small number of twentieth century teachers, and the differences between them reflect the emphases of those individuals.
Flowing sequences linking posture to breath, held static postures with props and precise alignment, fixed sequences practised in order, and heated rooms with set scripts all originate in specific lineages within roughly the same period.
Which means style differences are a matter of recent pedagogical choice rather than of ancient schools.
Teacher training
The commercial structure worth understanding before paying for anything.
The widely referenced two-hundred-hour qualification is a registry standard maintained by a private organisation, not a regulated professional credential.
Which means the term teacher covers an enormous range of actual competence, and there is no protected title.
Training in anatomy, contraindications and injury recognition varies considerably between programmes and is frequently minimal.
Asking a prospective teacher what training they have in working with injuries is a reasonable question, and the answer is informative.
Breath work in class
Worth a note since it appears in most classes with varying degrees of instruction.
Basic breath regulation alongside movement is generally uncontroversial and reasonably safe.
More intensive practices involving prolonged breath retention have genuine physiological effects and are taught in some classes without screening.
Anyone with high blood pressure, a cardiac condition, glaucoma or who is pregnant should ask specifically before participating in those, since the standard contraindications are well established and not always communicated.