Adverse effects rate
This is the first study reporting adverse effects of yoga in German yoga users. Previous studies have been conducted internationally, and have reported injury prevalence ranging from 2.4% (Australia) [24] to 62% (Finland, 110 participants surveyed) [23]. The differences in reported injury prevalence rates are significant, and are likely to be due to the survey format and the time frame in which participants experienced adverse effects.
Analysis of the injuries from yoga users in our study has also revealed that on average 0.60 injuries were reported every 1000 h of yoga practice, with large differences between the yoga styles. Power yoga, a physically demanding yoga style using flowing sequences of yoga postures, was found to be the most associated with adverse effects and was associated with 1.50 injuries per 1000 h of practice in our study. Similar rates of injuries have been reported previously [23]. A common factor with the yoga types associated with the most adverse effects in our study was that they emphasized postures over other aspects such as meditation or breathing exercises (or at least promoted more vigorous physical postures). Focusing on physical postures at the expense of other fundamental components of whole-practice yoga has been criticized as reductionist and incompatible with traditional practices [28], and emphasizing the importance of non-physical aspects of yoga to align with traditional practice may be one way to reduce the risk of adverse effects.
Compared to other types of sports and exercises, however, the overall injury rate of yoga per 1000 practice hours appears to be relatively low. Previous studies reported incidence rates from 2.5 injuries per 1000 h for general cardiovascular fitness activities [29] or running [30], to 3.7 injuries per 1000 h for soccer [31], to 5.0 injuries per 1000 h for tennis [29] and 8.0 injuries per 1000 h for skiing [29]. Strongman or strength athletics were reported to result in 4.5–6.1 injuries per 1000 h, and highland games in 7.5 injuries per 1000 h of practice [32]. These figures suggest that yoga appears to be as safe or safer when compared to other exercise types.
Types of adverse effects
The present study found that the vast majority of adverse effects from yoga affected the musculoskeletal system. These findings are mostly in line with findings from previous studies, which mainly reporting muscle or joint pain or strains [22, 24]. The present study however also found several serious adverse effects, ranging from joint injuries to bone fractures and disc prolapse, which may not be amenable to full recovery, potentially affecting longer-term health and well-being.
This study was the first to assess whether participants had recovered from their reported injuries. Findings from our study suggest that nearly one in four participants with acute injuries resulting from their yoga practice - and more than half of those with chronic adverse effects from their yoga practice – reported that they did not fully recover from their injuries. A previous study found that the number of yoga injuries requiring medical attention has been rising in the past decades [25], and emergency departments reported injuries to muscles and soft tissues, fractures, contusions and dislocations. While the number of severe injuries associated with yoga is relatively small (4.6% requiring medical treatment) [24], these findings suggest further attention on yoga-associated adverse events is warranted, and further studies are needed to identify the circumstances leading to those severe injuries, as well as to examine and identify effective ways in which such injuries can be avoided.
While the vast majority of adverse effects reported in our study were musculoskeletal, some participants in this study also reported adverse effects affecting other areas, including one case of a cerebral hemorrhage. Other adverse effects that have been reported in case reports and cross-sectional studies included injuries to the eyes, for example in participants with preexisting glaucoma [17, 20]. It is possible that adverse effects other than musculoskeletal injuries may not have been recognized as such by participants, and have been underreported due to the unclear association to yoga practice (for example due to the delayed manifestation of symptoms). It may be prudent to encourage physicians to include yoga in the list of physical activities undertaken when collecting patient histories, to ensure that any relevant yoga-related outcomes can be more accurately captured.
Predictors of adverse effects
One of the identified predictors for injuries among participants of our study was the specific yoga style practiced by participants, with vigorous forms of yoga being associated with higher risk of injuries. Vigorous yoga forms often combine postures into a series of movements, which could result in higher load on muscles, ligaments and joints compared to slow and more meditative yoga styles [20]. These more vigorous styles of yoga may also include higher frequencies of specific yoga postures found to be the cause of a large number of injuries, including hand stands, head stands or shoulder stands, forward and backward bends. This finding is supported by another study, [24] which reported the same exercises as the most common triggers of yoga adverse effects. Such exercises probably place large weights on body parts, for example the wrists for reversed positions or the knees in positions that require prolonged kneeling or flexion. As a result participants without sufficient preparation or training may experience pain or even injuries to the affected joints. Some studies even suggest that yoga practice may lead to meniscal damage [33], which is a risk factor for osteoarthritis and related disability [34]. However, a cross-sectional study conducted in Australia did not find higher rates of knee or other joint problems in yoga users as compared to yoga non-users [35], and such disparate findings indicate further research is warranted. Given that the joint load has been estimated based on correct execution of the exercise, with the assumption of a normal weight practitioner with no preexisting physical impairment, further studies are also needed to examine the joint load in everyday practitioners.
Another factor associated with increased risk of adverse effects among participants in our study is the presence of preexisting medical conditions or illnesses, including predispositions for certain injuries. This result confirms findings from previous studies [22, 24], showing that poor physical health and chronic disease significantly increase the risk of injuries during yoga.
Another important finding for our study is that yoga self-study without prior or current supervision is more likely to lead to adverse effects than supervised yoga practice. Self-study is an important part of yoga practice, and is often promoted in clinical trials to increase the total practice frequency [7,8,9, 11,12,13, 36]. However, there is also a plethora of self-practice DVDs and videos, or online courses available for those who want to learn and practice yoga by themselves. Physically demanding yoga postures and motion sequences may require surveillance by experienced instructors to ensure correct execution. Self-practicing individuals may execute postures incorrectly, or push themselves too hard to follow the instructors, thus increasing the risk for injuries. These results suggest that some form of regular or formal supervisory guidance may be beneficial for reducing adverse events associated with yoga practice. An interesting finding related to this point form our study is that participants practiced in class for only 84.9 min per week but for 166.3 min at home. This is most likely the case because not all participants actually attended any classes, with some practicing only at home.
Props, such as blocks and belts have been heavily discussed in the literature as being either beneficial [37] or hazardous [19]. Props were introduced into modern yoga practice to allow practitioners to access the benefits of yoga postures regardless of their physical condition or experience [37]. In our bivariate analysis the use of props slightly increased the frequency of acute adverse effects. However, in the logistic regression no associations between the use of props and injuries were found. As such the use of props cannot be considered hazardous in general, however precautions should be applied when practicing with props, such as ensuring correct handling of props (including securing the props when they are not used), and not applying props to push and exceed bodily limitations, to reduce potential yoga-associated adverse events.
It could also be expected that injury rates differ by motivations for yoga practice, particularly if those who are motivated for fitness reasons are drawn to more vigorous forms of yoga. In this survey, more than 60% of participants were currently practicing yoga for general prevention or stress management and only 1.5% for fitness reasons; however, motivation for yoga practice was not associated with injury rates (data not shown). Comparable to other forms of physical activity, the risk of injuries did not differ between genders [32].
Limitations
While the sample in our study comprised predominantly female participants with higher educational degrees, and is thus not representative of the general population, it may be representative of yoga users given that women are more likely to practice yoga in general. For example the reported ratio of female to male yoga users in the US was 3:1 [1], and almost 9:1 in Germany [4], indicating that the proportion of women in this sample is a relatively close reflection of their proportion in yoga practitioners in Germany. A further potential limitation of the survey is that it is based on self-reported data with no limitation regarding the time point of injury, and as such not all injuries may have been recollected and reported. On the other hand, not limiting the time period allowed the calculation the lifetime prevalence of yoga-associated adverse effects. Assessing a period prevalence instead might have resulted in a too low number of events to be able to calculate relationships. Additionally, since a snowball system was used for recruitment, the response rate cannot be determined. The increased risk of acute adverse effects with increasing yoga philosophy study is counterintuitive and difficult to interpret.
Practical implications
The findings of this study have a number of practical implications for a safe yoga practice. Firstly, individuals with preexisting chronic conditions need to be cautious, and should preference yoga classes led by certified and experienced practitioners. Specialized yoga therapy classes might be preferable over standard yoga classes. It might also be wise for patients with preexisting chronic conditions to further consult with their general practitioner or specialist before taking up yoga practice. It is also recommended that individuals with specific conditions avoid specific positions (e.g. those with hypertension or glaucoma should avoid inversion poses, individuals with joint problems should avoid extreme twists etc.). Our findings also highlight the importance of qualified yoga instructors, who appear to reduce the risk of adverse effects in yoga users. Beginners should learn and practice yoga under supervision, and only self-study when they feel confident and are capable to execute postures correctly and safely. Finally, props may be used to improve safety, for example to support individuals in exercises requiring balance, however they should be used sparingly and not solely as a means to overcome physical limitations.
