Yoga is emerging as a widely practiced complementary and integrative therapy. This paper brings to light the utility of yoga as a non-invasive means of treating many disorders and improving the overall quality of life. Its efficacy in various neurological disorders has been described in this review; however, these studies had certain shortcomings. These reflect areas where significant gaps in research exist and provide direction for those wishing to exploit the great potential that this field promises.
The goal of this review paper was to evaluate the credibility of yoga as a complementary treatment and management modality in different neurological disorders. Although our review provided some insight into the benefits of yoga in various neurological disorders, most of the studies reviewed were only in the initial stages of understanding the clinical (or symptomatic) benefits of yoga. Furthermore, most of these trials had inadequacies in their study designs. Therefore, until studies involving double-blinding and randomization with larger samples are employed, these benefits cannot be substantiated to draw proven conclusions of the benefits of yoga. Once that has been achieved; however, the next phase would be to observe and understand the actual physiological changes and the modifications in pathology occurring with the practice of yoga. Until that time, a discussion or classification of the benefits of yoga would be highly speculative. However, it is of utmost importance to understand these shortcomings in the study designs used till date, for guiding investigators wishing to pursue this cause further. A critical analysis of the studies reviewed is presented.
As with any emerging treatment modality, establishing the most effective method is difficult. In commencing this review article, the first problem recognized was the broad classification of yoga. Many studies used the term yoga liberally without specifically identifying the type of yoga under investigation. There are four classes of yoga with numerous subtypes under each. Among the various articles reviewed, only a few provided detailed descriptions of the yoga programs enlisted. A meta-analysis requires a thorough description of each program for optimal comparison of study results. The sequence of yoga postures can be ascertained from a sequence of posture names, but more detailed descriptions are essential to future studies seeking to replicate or generalize the results. A standardization of yoga exercises for research purposes would reduce interpretative confusion and normalize the field. As the use of therapeutic effects of yoga continues to be assessed, it is imperative that a detailed description of the type of yoga used is defined.
Studies of neurological disorders, like epilepsy, have shown improvements attributed to yoga. However, it is important to recognize that behavioral modification and altered lifestyle may have accounted for the improved outcomes. The study by Sirven et al
] exhibited that the percentage of individuals who benefited from yoga was among the highest in all CAM modalities, but the number of individuals actually following the regimen was not very high. It would be interesting to see whether the effects would be amplified with a strict regimen followed closely by all subjects.
Bastille et al
] demonstrated the benefits of yoga among post-stroke patients, but the measures tested were not very sensitive. For instance, the Berg Balance Scale (BBS) was not very sensitive to changes that may occur in some people with high-level balance deficits, a finding previously reported in another study.[63
] An example of this was observed in one of the subjects of the study. The subject had a mean BBS baseline score that was just 4 points from the maximum possible score before the intervention began. Thus, in future studies, it is recommended that other measures, which are more sensitive to changes in postural stability, such as the Dynamic Gait Index[64
] or measures of postural sway, be used. Furthermore, the Timed Movement Battery appears to be an appropriate measure of timed mobility, but this does not provide any information about the factors that may be influencing speed of movement. In addition, limited information is available to determine the clinically meaningful changes in TMB scores. The inclusion of additional impairment measures is recommended to clarify the relationship between changes in impairments and changes in speed of performing movement tasks. This will elucidate the effects of yoga on flexibility, muscle force, endurance, and motor function in people with chronic post-stroke hemiparesis. Most importantly, all such studies measuring the benefits of yoga-based exercise programs should be done with larger samples and control subjects to offer better statistical support.
In the study by Oken,[47
] yoga and aerobic exercise were effective in relieving fatigue in MS patients. However, the mechanism of action of these improvements is unclear and may not relate directly to either yoga or aerobic exercise. Socialization, placebo, and self-efficacy effects may have influenced the results. Both interventions had an element of socialization that may have contributed to some benefits. Prior investigators have also commented on the lack of an adequate social control group in similar exercise intervention studies as a placebo effect may account for some of the findings.[65
] One study has already shown that psychological benefits of an aerobic exercise intervention in a group of healthy young adults could be increased simply by informing subjects that the exercise program was specifically designed to improve psychological well-being.[66
] The issues of placebo effect and self-efficacy, both of which may have a significant impact,[67
] are difficult to adequately control in non-blind behavioral interventions. Additionally, the absence of statistically significant effects on the mood and cognitive measures needs to be interpreted cautiously, because there is a possibility that enhanced mood contributed to these improvements in quality of life and fatigue. This issue is still open to further investigation.
An important observation made in this review is that most of these studies were conducted in India where the philosophy and practice of yoga originated. The samples reviewed mostly focused on one geographical region where yoga is particularly ingrained in the culture. Generalizing these findings to other parts of the world and to different populations remains difficult. Only a very small number of studies have actually addressed variables of interest specific to minorities in the United States (Blacks, Hispanics, and Asians). These populations are distinct in their respective vulnerabilities to physical inactivity and specific disorders like type 2 diabetes etc.[69
] Future studies, such as double-blind controlled ones, should assess the therapeutic value of yoga in US minority populations as well.
In the preliminary study for CTS, the yoga-based regimen was more effective than wrist splinting and no supplementary treatment control in relieving some symptoms and signs.[58
] However, as with most of the studies done with complementary therapies, this study was limited by small sample size and lack of generalization. The participants in the study continued to observe improvements in their CTS symptoms even after the yoga treatment was terminated. Further studies are needed to ascertain whether a single course of yoga intervention with occasional reinforcement can be effective for long-term relief. Since health problems such as CTS are the leading cause of lost earnings in the workplace, continued evaluations of outcomes are needed to assess long-term effects of yoga on CTS symptoms, lost time from work, and patient satisfaction.
Another aspect, which remains to be determined, is the optimal intensity and duration required to maximize the effectiveness of yoga programs. Because the metabolic equivalent of yoga is low, it can be said that increasing the frequency will increase the benefits; however, these factors cannot be judged as many articles did not clarify the intensity or usage level of the yoga program studied. Moreover, most of the studies focused only on the short-term health benefits of yoga with very few including follow-up data; thus, a more comprehensive understanding is still needed in the maintenance aspect of yoga to achieve long term effects. It remains to be determined whether more intensive training can improve the likelihood of adopting and maintaining an active yoga practice in long run. It is necessary to have well-designed studies with larger sample sizes to determine the validity of yoga as an effective therapy for neurological disorders. Furthermore, since yoga is a physical activity, it remains difficult to perform large scale randomized controlled trials and even more difficult to sustain blindness over the course of months. Despite the many shortcomings in the literature, the potential of yoga in treating neurological disorders remains vast. Yoga as a prophylaxis can be used as an important tool for health promotion and disease prevention with minimal cost.