A survey of 2508 yoga class attendees and 271 yoga therapists in Japan (released March 2015 in BioPsychoSocial Medicine) found that nearly 30% of attendees experienced an adverse event (defined as a "undesirable symptoms or responses that occurred during a yoga class") during class.
Over half of the yoga class attendees (53.5%) had chronic diseases and 1063 (42.3%) were being prescribed medications at hospitals. In terms of age, 36.5% of the class participants were in their 60s and 16.3% in their 70s.
Study Population Diseases. Matsushita and Oka BioPsychoSocial Medicine 2015 9:9 doi:10.1186/s13030-015-0037-1
The most common events were musculoskeletal (muscle pain, joint pain, and muscle cramps), followed by neurological symptoms (dizziness, numbness), and respiratory symptoms (coughing, nasal congestion). Most of the events (63.8%) were mild symptoms that did not interfere with class participation.
Adverse events were more severe in participants over age 70 and those with chronic musculoskeletal disorders like osteoporosis. Eight cases required emergency transport: post-class subarachnoid hemorrhage (bleeding in the space between the brain and tissues surrounding the brain), subluxation (partial dislocation) of the hip joint, backward fall, sudden attack of abdominal pain, dizziness, arrhythmia, hyperventilation, and inability to move due to illness and increased anxiety. Fourteen cases required medical examinations: contusion and bone fracture from a fall due to loss of balance, fall due to illness, illness due to elevation of blood pressure, fall due to physical unsteadiness, severe pain of the hip joint, knee joint and abdomen, pain due to meniscal injury and Achilles tendon rupture, hyperventilation, dizziness, and palpitation.
There are a few notable limitations regarding the implications of this survey on yoga safety. One major issue, unfortunately common in this area of scientific literature on yoga safety, is that the type of yoga practiced, yoga sequence and postures, the presence/absence of warm-up (which is thought to decrease musculoskeletal injuries) are not specified in the study nor does the study document at which point the event occurs (e.g., which postures, early/late in class). Secondly, the study does not necessarily prove causation, meaning that the adverse events were associated during yoga class but it is unclear whether yoga actually caused the symptoms, in particular the more mild ones like coughing, which would require a more specific investigation. Third, the relative risk of yoga (compared to another form of exercise or movement), such as walking, is unclear (i.e., would walking have induced a similar rate of adverse events in this population?).
The study is helpful, however, in a documenting the types of injuries in a population with chronic diseases and pre-existing medical conditions and examines risk factors to maintain a safer practice. In particular, mental strain was associated with 4 times increased risk for adverse events, suggesting that if the idea of yoga class is more stressful than positive, then it may be safer to wait to practice at another time or to bring more awareness to your practice.
Below is the chart listing causes of adverse events in the opinion of the yoga therapist.
The study supports the importance of yoga instructors in assessing pre-existing medical conditions or injuries prior to practice (and for yoga students with medical conditions in letting instructors know about their conditions) in order to make safe modifications or adjustments to one's individual practice. A 2013 review by Cramer et al. of case studies and reports, ranging from 1969 to 2012, found that the vast majority (67 out of 76 reported events) of adverse events in yoga occurred in cases that involved pre-existing medical conditions, including glaucoma, osteopenia, and asthma and connective tissues disorders. The most common injuries involved the musculoskeletal system, including fractures, ligament tears, and joint injuries. The second most common injuries were orbital adverse events, including acute glaucoma, worsening of chronic glaucoma, and orbital vein occlusion. Glaucoma in particular is important to be aware of since inversion postures like headstand has been shown to increase intraocular pressure by twofold and should thus be cautioned against for those with glaucoma.
Further scientific studies of yoga safety will continue to help inform yoga teachers and students about creating a safe and healthy yoga practice.
Matsushita, T, Oka T. A large-scale survey of adverse events experienced in yoga classes. BioPsychoSocial Medicine 2015 9:9 doi:10.1186/s13030-015-0037-1
Cramer H, Krucoff C, Dobos G: Adverse events associated with yoga: a systematic review of published case reports and case series. PLoS ONE 2013, 8(10):e75515