domingo, 26 de abril de 2015

Efficiency of Modified Yoga Positions to Treat Postural Pathologies Associated Pain: A Literature Review
José Luís Pimentel do Rosário*
State University of the West-Center–UNICENTRO, PR-Brazil
Keywords
Manual therapy; Muscular chain; Posture; Yoga
Introduction
Static posture refers to the alignment and maintenance of body segments in certain positions. Some postural misalignments may adversely affect the muscular efficiency, predispose individuals to pain and pathological musculoskeletal conditions, and provoke unaesthetic alterations [1,2].
According to Kappler [3], a good postural balance creates less stress on joints, requires less muscle activity to maintain balance and therefore, is the position of maximum effectiveness. An imbalanced posture should be compensated by changes in joint position, which in turn, must be maintained by an increase in muscle activity and cause injuries [3], as well as the imbalanced muscles [4,5]. Thus, the postural imbalance results in excess of energy consumption [3].
A number of authors have stated that if body segments are kept out of alignment for extended periods, some of the muscles involved are used in a shortened position, as a consequence. These muscles are usually seen as strong, while their antagonists are taken to be elongated and weak [6], and this is one of the effects of poor posture. These deviations can be unsightly, adversely affecting muscular efficiency, predisposing individuals to pathologic musculoskeletal conditions. One of the major symptoms of postural change is pain [1].
According to Lee [7], good posture creates the least amount of joint stress, and requires the least amount of muscle activity. Consequently, it is the position of maximum efficiency. The same author also described how a deviation from optimal positioning should be compensated by changes in the joint position, which in turn, must be maintained by an increase in muscle activity. Therefore, postural instability results in an excess of power consumption. This change in joint position described by Lee [7], is very similar to the concept of chiropractic subluxation. Generations of chiropractors have claimed that a large percentage of all diseases are caused by subluxation [8].
In 1947, the kinesiotherapist Françoise Mézières, the mother of therapies based in muscular chain [9,10], stated that human muscles are completely inter-related, and demonstrated that there is not just a single muscle that causes bad posture, but chains of muscles that can end up causing a pathology in a specific place from a generalized tension. Therefore, a localized muscular action provokes reactions at a distance, underlining that the root of the problem can be distant from where the patient feels pain [11].
The Muscular Chain Therapy (MCT) uses this postural concept, observed and elaborated by Mézières, in order to understand the posture. For the evaluation, MCT uses two yoga positions and five for the treatment. These yoga positions were modified, aiming to stretch at the same time, all the muscles of the chain to be worked. A number of existing scientific studies have approached MCT or similar techniques based on Meziérès muscular chains and modified yoga postures, with assistance of a therapist. These studies have produced results in treating various musculoskeletal conditions [12-20].
Considering the fact that poor posture causes joint positioning changes, and that this malposition can cause pain, the origin of which is far from the location, it is important to understand the functioning and application of the muscular chains, and to develop a therapy that successfully uses this theory in clinical practice.
Materials and Methods
The Medline and Lilacs databases were consulted for relevant articles from 2002 to 2012, with the key words “posture” and “postural”. The abstracts of articles were read in order to confirm, if they satisfied the inclusion criteria. Only articles and books in English, Portuguese, French, Italian or Spanish were considered, and some type of muscular chain technique must have been used or described, as in the following description.
Muscular Chains Therapy
Muscular chains are formed by gravitational muscles that work synergistically in the same chain, and it is very well explained by the theory of Anatomy Trains [21], and of course, the maintenance of the standing position against the action of gravity [22]. The concept of muscular chains is based on the observation that the shortening of a muscle creates compensation in the adjacent and also distant muscles. In this study, the fascial treatment was not added, in order to emphasize the muscles. Therefore, the MCT is a global stretching technique that uses postural positions for stretching several muscles simultaneously, rather than treating an isolated muscle [1]. These muscles belong to the same muscular chain [22]. Basically, we have two main chains: anterior and posterior, which have a lot of similarities with the superficial frontal line and Superficial back line [21], respectively.
The Posterior Chain includes the following muscles: Gastrocnemius and Soleus; Flexor Hallucis Brevis; Flexor Hallucis Longus; Short Flexor of Fingers and Flexor Digitorum Longus; Adductor Hallucis; Abductor Hallucis; Hamstrings (Semitendinosus; Semimembranosus and Biceps Femoris); popliteal; Gluteus maximus. It also includes the following: Paraspinals: Iliocostalis Lumborum; Iliocostalis Thoracis; Iliocostalis Cervicis; Longissimus Thoracis; Longissimus Cervicis; Longissimus Capitis; Spinalis Thoracis; Spinalis Cervicis; Spinalis Capitis; Semispinalis Dorsi; Semispinalis Cervicis; Semispinalis Capitis; Multifidus; Rotatores; Interspinales; Intertransversarii [22,23].
The Anterior Chain is divided in two: The Inspiratory Chain and the Hip Internal Rotator Chain.
The Inspiratory Chain includes the following muscles: Scalenus; Sternocleidomastoid; Pectoralis Minor; Intercostals; Diaphragm [22,23].
The Hip Internal Rotator Chain includes the following muscles: Iliacus; Psoas Minor; Psoas Major; Adductor brevis; Adductor longus; Adductor magnus; Gracilis; Pectineus [22,23].
The Arm Chains can be divided in three: the Shoulder Adductor Chain that may be considered part of Anterior Chain; the Shoulder Elevator-Adductor Chain that may be considered part of the Posterior Chain; and the Arm Internal Rotator Chain which is neutral, because it is associated to both Anterior and Posterior Chains, and can also be stretched in Anterior and Posterior postures.
The Arm Internal Rotator Chain includes the following muscles: Pectoralis Major; Brachial Biceps and Brachialis; Pronator Teres and Pronator Quadratus; Flexor Digitorum Profundus; Flexor Digitorum Superficialis; Flexor Pollicis Longus and Adductor Pollicis; Abductor Pollicis Brevis; Flexor Pollicis Brevis; Opponens Pollicis [22,23].
The Shoulder Elevator-Adductor Chain includes the following muscles: Subscapularis; Deltoid; Upper Trapezius [22,23].
The Shoulder Adductor Chain includes the following muscles: Pectoral Major; Coracobraquialis; Subscapularis [22,23].
This muscular chain concept differs from the segmental stretch, which treats each shortened muscle separately, usually those directly involved in the joint with decreased range of motion. MCT applies a long duration stretch, which lasts approximately 15 minutes per postural position, while coupled with eccentric physical exertion for the posture maintenance, featuring an active form of stretching [1,23]. Clinically, the MCT has been efficient treating postural deviations and providing greater flexibility [23].
Assessment with MCT is described according to Rosário et al. [24].
Assessment
Examination of the anterior chain: The anterior muscles that can raise the lordosis are the diaphragm, the iliopsoas and the pubic adductors. They pull the lumbar spine forward, placing the pelvis in anteversion. Therefore, it was necessary to rectify the lumbar in order to test this chain. The Tadasana – Mountain Pose – is used to assess the Anterior Chain (Figure 4). Patients who have either shortening or tension in this chain exhibit compensatory changes.
Assessment Steps
1. Place the individual standing, with their heels together.
2. Rectify lumbar lordosis by retroversion.
3. Observe the compensation, which may be one of the following:
- Leaning the torso back;
- Bending the knees. A small flexion is normal;
- Chest blocked in an inspiratory position;
- Protrusion of the head and shoulders.
Examination of the posterior chain: The posterior spinal muscles flatten and push the lumbar spine back, leading to pelvis retroversion, with a tendency to keep the sacrum in a horizontal position. It is necessary to flex the trunk, in order to assess this chain. The flexion alone can provide some clues about posture. Since this chain tends to invert the lumbar curve causing a kyphosis, it is important to request a small lumbar lordosis with the hip flexion, in order to put this chain in full tension. Consequently, the trunk will be raised, but a loosening of hip flexion will be avoided. When it exists, shortening becomes obvious at this stage. The Shaktyasana–The Shakty goddess pose–is used to assess the Posterior Chain (Figure 5).
Assessment steps
1. The subject must lean forward with the knees straight and the heels together. Note if the curvature of the spine and the spinous processes are all clearly visible.
2. To complete the test, align the lumbar spine, requesting a small lumbar lordosis.
3. A shortened individual will extend the trunk, opening the hip angle of flexion. Another possible abnormality is the opening of the tibio-tarsal angle, which is the angle formed between the foot and the tibia.
Comparison of chains: The most compromised chain is the one presenting the highest compensation in the test. This chain is the first to be treated.
Examination of the arm chains: If the anterior chain is the most compromised, this test should be done in a standing position, with rectification of the lumbar spine. If the posterior chain is the most compromised, the test should be performed seated, holding a small lordosis. After this positioning, it is essential to confirm that the thoracic curve is not flattened and to add adduction and depression of the scapula, external rotation of the arm, forearm supination and extension of the wrist and fingers.
After aligning the posture, it is necessary to observe the compensation generated by both abduction, and then adduction of the upper limbs. If abduction generated more compensation than adduction of the upper limbs, it was given priority in terms of treatment. If adduction compensated more, adduction was the priority.
Treatment
Treatment consists of two 15-minute postures. Before treatment, the patients were taught how to separate their breathing by region: apical; lower ribs and diaphragmatic breathing, in order to help the maintenance of posture. The selection of posture was based on the assessment described above. If there were more alterations in the posterior chain, two postures of the posterior chain were performed. If there were more alterations in the anterior chain, two postures of the anterior chain were performed. If the two chains exhibited similar alterations, treatment involved one posture of each chain. The therapist should choose a lie down posture in the following circumstances:
1. More work was needed on breathing.
2. Pain or disability prevented the patient from remaining standing or sitting.
3. If the work was focused on the head, neck or upper limbs.
Postures with load (sitting or standing) should be selected in the following cases:
1. Focus on the trunk or lower limbs.
2. To provide a stronger stretch or improve muscle strength.
All postures must be performed actively by the patient, which helps to promote proprioception and eccentric stretching. It is possible to perform at least two postures in one session. Sessions are conducted once or twice a week, depending on whether the problem to be treated is chronic or acute. The muscles involved in each of the modified yoga positions are those found in the posterior and anterior Muscular Chains. Note that acute cases may involve less therapy time and a greater session frequency [10,25].
The following is a description of postures according to Rosário et al. [24].
Supta Baddha Konasana: Reclining Bound Angle Pose (anterior chain) (Figure 1)
- The patient is positioned in the supine decubitus, with the arms against the body;
- The patient puts the soles of the feet together;
- As a rule, the total external rotation of the femur should be sought. If the patient has excessive external rotation of the femur, a neutral position of femur rotation can be adopted;
- Neck traction, while maintaining physiological neck lordosis;
- The tension point of the posture can be found by bringing the heels forward, extending the knees, leading to more difficulty in keeping the patient’s lower back flat against the table.
Viparita Karani: Inverted Legs Pose (posterior chain) (Figure 2)
- The patient is positioned in the supine decubitus, with the arms against the body;
- The patient puts the soles of the feet together;
- As a rule, the total external rotation of the femur should be sought. If the patient has excessive external rotation of the femur, a neutral position of femur rotation can be adopted;
- Neck traction while maintaining physiological neck lordosis;
-The therapist flexes the patient’s hip holding them by the heels. Alternatively, the therapist can use a support for the heels (Figure 2), in order to free the hands for treatment;
- The tension point of the posture can be found by bringing the heels forward, extending the knees, leading to more difficulty in keeping the patient’s lower back flat against the table.
Tadasana: Mountain Pose – against the wall (anterior chain) (Figure 3)
- Check the distance from the wall. The closer to the wall, the more difficult the exercise is.
- The knees are slightly semi-flexed and rotated laterally.
- The pelvis is in slight retroversion with the dorsal and lumbar regions against the wall.
- Thoracic and cervical curves maintained in physiological position; lumbar rectified.
- Upper limbs: place the shoulder blades against the wall, with the arms abducted 30° in neutral rotation, the elbows extended, supinated forearms, wrists in a neutral position and fingers relaxed.
Tadasana: Mountain Pose – free version (anterior chain) (Figure 4)
- Similar to the previous position, but without the support of the wall. The therapist supports the patient’s occipital.
Shaktyasana: The Shakty goddess pose (posterior chain) (Figure 5)
- Similar to the posture standing in the center, but maximum hip flexion is possible, without reversing the physiological curves of the spine.
Dandasana: Staff Pose (posterior chain) (Figure 6)
- The patient sits with a hip flexion that imposes difficulty in maintaining the physiological curves of the spine, without ever reversing them.
- The therapist supports the patient’s occipital with his hand.
- The knees are bent and the soles of the feet are together.
The starting position would be Baddha Konasana (Bound Angle Pose), moving to Dandasana (Staff Pose).
Evolution of postures
During the 20 minutes of posture, the therapist must seek to maintain the symmetry of the patient. The difficulty of the posture is gradually increased, until the patient can go no further. The name of the evolution of the posture is applied to this process, and it must follow certain rules:
- At no time is it permissible to reverse the physiological curves;
- All the postures need gradual extension of the lower limbs;
- In the final minutes of the postures, it’s important to make a dorsiflexion. In standing postures a ramp is used;
- The postures of the posterior chain need a gradual increase in hip flexion;
- The evolution of arm chains in all postures is a gradual increase of the adduction of the shoulder blades, shoulder external rotation, forearm supination, wrist and finger extension;
- There is only evolution in adduction or abduction of the arms in the lying postures. In the standing postures, the arms remain adducted and close to the body at all times.
Results
Beyond the obvious indication of posture treatment, there are some musculoskeletal problems treated by therapies related to muscular chain. The present work had a review of articles that used the Muscular Chain concept and at least one of the Yoga postures previously described, or similar to one of them for treatment. Canto et al. [13] studied the efficiency of MCT in individuals with lower back pain, in terms of the level of pain and functional disability. Thirty-five individuals were assessed with a visual analog pain scale and the Roland Morris functional disability questionnaire, at the time of the first and tenth treatment session. In total, 85.7% of the participants reported a decrease in the level of pain at the end of treatment, and 77.1% of the subjects recorded a lower score on the Roland Morris questionnaire.
Moreira and Soares [17] studied a group of five women aged between 20 and 30 years. The women were submitted to physical therapy to correct their posture, and to reduce the pain caused by postural abnormalities. The patients were radiographed one week after therapeutic discharge. The postural improvement was evidenced by the retraction of the shoulder. Despite the small number of patients, the radiographic image is a high point of the study. Based on this study, it is possible to see that some of the complaints of musculoskeletal pain may be related to postural problems. Rossi et al. [20] assessed the effect of an application of the lying hip extension posture on 11 photographic postural variables. Of these variables, only 4 recorded significant improvements, and these four were all related to the head. Rosário et al. [24] obtained results in 3 of 6 variables with eight postural reeducation sessions, and there was no improvement in the shoulders and head. This highlights the fact that therapists place emphasis on postural correction, which may be more influential in a chosen segment. These studies revive the discussion, with a focus on posture and not on pain, about the time required for postural corrections and relief from the related pain. Rossi et al. [20] obtained the postural result with one posture, and the present study recorded pain reduction with one session and two postures.
Marques et al. [16] assessed the effect of postural treatment on fibromyalgia. Twenty patients that had been diagnosed with fibromyalgia were treated for six sessions on average. Of the 20 patients, 18 reported some improvement, and 65% rated it as excellent or good, whereas 25% reported it as fair and only 10% reported no improvement.
Although fibromyalgia is listed as a rheumatologic disease, these data are similar to the results of the present study.
Basso et al. [12] decreased the pain of 20 patients with temporomandibular disorders, using 10 muscular chain treatment sessions. Gil et al. [14] decreased back pain in pregnant women in 8 weeks. Heredia and Rodrigues [26] relieved the pain of patients with epidural fibrosis in post-operative lumbar disc herniation with 15 sessions, also using analog scales.
Teodori et al. [27] conducted an interesting case study. Changes in plantar pressure distribution and the location of the center of force were assessed in a subject with a history of right ankle sprain, using a pressure platform, with free bipedal support and with the eyes open. Asymmetry was found in the distribution of plantar pressure applied to the subject in one postural reeducation session, and was followed by an assessment of the pressure platform, immediately after the intervention, and after 7, 14 and 30 days. The results clearly showed a recovery of symmetry, which continued for 7 days. After this period, there was a gradual recovery of asymmetry, although the initial values had not been attained after 30 days. Although a case study, if the data of this author is correct for the general population and most musculoskeletal pain is related to posture, one MCT session, as performed in the present study, would have the effect of pain resolution for seven days, and would remain in effect for 30 days or more, in cases of chronic pain.
do Rosario et al. [23] argue that this type of postural treatment technique does not act on posture simply by stretching, since a 15-minute posture provided similar results for hamstring flexibility, as a 30-second hamstring stretch. Body awareness and the active maintenance of better joint positioning, reducing an existing subluxation, can exert their influence on postural adjustment and consequently, solve related pain. Whatever the reason for the effect is, previous studies have shown that MCT causes a great improvement in the efficiency of a musculoskeletal pain source.
Conclusion
With the data obtained in the present study, it is possible to state that MCT, using modified yoga positions, is an efficient technique in terms of improving posture, reducing pain, and solving related musculoskeletal problems.
Further studies are required to understand how MCT, using modified yoga positions has the above impact, what musculoskeletel conditions that can be treated effectively by this method, as well as those that cannot, and the optimal time and frequency of application for each of these pathologies.
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Open Access
How might Yoga Work? An Overview of Potential Underlying Mechanisms
Marcy C. McCall*
M. Sc. Kellogg College, University of Oxford, UK
Introduction
Popular and academic interest in yoga for treatment of health conditions are increasing at an alarming rate while over 30 million people claim to practice yoga for health benefit worldwide [1]. The practice of yoga originates from 5000 BCE in India to combine specific postures (asanas), breathing techniques (pranayama), meditative techniques (dhyana), chants (mantras) and wisdom teachings (sutras) to encourage union with body and mind [2]. Yoga therapy is the “process of empowering individuals to progress toward improved health and well-being through the application of the philosophy and practice of Yoga” [3]. Today, nearly 14 million Americans (6.1% of the population) say that a doctor or therapist has recommended yoga to them for their health condition [4]. In the United Kingdom, national healthcare services promote yoga as a safe and effective way to promote physical activity, improving strength, balance and flexibility as well as a potential benefit for people with high blood pressure, heart disease, aches and pains, depression and stress [5].
Over 2000 health and yoga-related journal articles are published online (www.ncbi.nlm.nih.gov/pubmed). In 2012, 274 new yoga titles were added to the PubMed database for healthcare research. A recent summary (2012) indicates that there is relatively strong evidence to suggest that yoga may have beneficial effects for painassociated disability and mental health [6]. A preceding overview (2010) shows unanimously positive evidence emerged for depression and cardiovascular risk reduction with yoga, with little supporting evidence to suggest benefit for patients with epilepsy, asthma or various pain conditions [7]. A further clinical review suggests that psychological symptoms and disorders (anxiety, depression, sleep), pain syndromes, autoimmune conditions (asthma, multiple sclerosis), immune conditions (lymphoma, breast cancer), pregnancy and weight loss can all be positively affected by yoga [8]. From an evidence-based healthcare perspective, the hypothetical underlying mechanisms to explain potential effects of yoga are in the early stages of investigation. In response to the Medical Research Council’s guidelines for evaluating complex interventions [9,10], a coherent theoretical basis should be established in advance of further research development.
Purpose of this Review
As evidence suggests, yoga has a potential role in the prevention and treatment of numerous health conditions. The theoretical basis for health effects is important to clinicians, researchers and yoga practitioners. The purpose of this literature review is to synthesize the current hypotheses and scientific evidence for underlying mechanisms of yoga intervention.
Methodology
Inclusion criteria
Type of articles: Any clinical investigation, review or evidence synthesis that explores potential underlying mechanisms for yoga’s effect in a health-related context is included. Authors must name yoga as the primary focus of their research. To improve the quality of data, only peer-reviewed articles published on-line within public medical research databases after January 1, 2006 are included. Hypotheses that are presented without sufficient scientific evidence are set aside and presented as emergent hypotheses.
Type of mechanisms: Any yoga mechanism or description that includes underlying effects of practicing yoga or explanations supported with scientific inquiry or preliminary evidence is included. Health outcomes such as blood pressure, reducing body weight or decreasing stress are insufficient for inclusion, though may be included if underlying mechanisms of these outcomes are discussed.
Type of yoga: Any type of yoga is included for review. A standardized definition of yoga in research is not available at this time. For the purposes of this review, a broad and conventional definition is a pragmatic choice, where the described yoga intervention must include one or more of the following characteristics: (breathing techniques), asana (postures) and dhyana (meditation) and/or other yoga teachings.
Exclusion criteria
Articles that discuss interventions similar to yoga (i.e., massage, tai chi, talk therapy) are excluded. Research protocols or papers that discuss yoga mechanisms only in their introduction or study rationale are not included.
Search strategy
Databases: An on-line search of three scholarly databases includes the Cochrane Library, PubMed and Scopus databases. Conferences and websites of yoga institutions and references from found articles are also searched. Hand-searches in yoga-specific journals and books also performed to ensure a comprehensive search.
Online search terms and limitations: A rapid systematic search employs free-text terms: [yoga] AND [(mechanism OR pathway OR effect) AND (clinic* OR review)]. The literature search is current as of 1 December 2012.
Results
Description of included articles
The title-search identified 454 potential articles, 110 abstracts were screened and 24 full-text articles assessed for eligibility. Eighteen original articles are included in this literature review (Figure 1). A variety of outcome effects are presented in the literature, including treatment and prevention of cardiovascular disease (CVD), diabetes, obesity, arthritis, cancer, epilepsy and erectile dysfunction. Psychological wellbeing, relaxation, decrease in depression and anxiety, delayed aging, improved pain management and sleep quality were also discussed. Five of the articles introduce potential mechanisms that lack empirical evidence and will be discussed separately as emerging hypotheses. Table 1 lists the characteristics of included studies.
The characteristics of yoga intervention are not explicitly reported in the majority of cases, although asana practice appears most commonly cited (17 articles). The Oswal study [11] examines the effect of pranayama and dhyana components of yoga only. Six articles were excluded after initial screening because of insufficient empirical evidence to support theories, or yoga mechanisms are not the focus of the paper, or the paper includes interventions other than yoga (Table 2).
One of the 18 included reports identifies an adverse effect of yoga [12]. In this case, a female practitioner developed thrombosis of the vertebrobasilar artery due to an intimal tear and suffered a subsequent stroke. The nature of this injury is attributed to adopting an unusual neck posture [13].
Quality of included articles
One included article is a systematic review of underlying mechanisms for yoga [14] and receives a high-quality rating (AMSTAR=9) [15]. One randomized control trial [9] (n=30) reports double blinding and shows reasonable effort to minimize bias and appears to follow the CONSORT [16] guidelines for transparency and effective reporting procedures. Three controlled trials [17-19] are included, though the quality of evidence is low due to selective recruitment and lack of randomization with no mention of blinding techniques. Furthermore, in two instances the reporting of results does not match the authors’ hypotheses [18] and conclusions [17]. The remaining articles (13) are literature reviews or clinical reports and do not report on methodological considerations such as search protocols, inclusion or exclusion criteria of studies or rating the quality of evidence.
Overview of mechanisms
The empirical evidence supporting underlying mechanisms for clinical effects of yoga is limited. A current systematic overview or review that thoroughly assesses the quality and weight of evidence to support or reject hypotheses has not been found. Research interest for mechanisms that examine pathways originating in the endocrine system, nervous system and cardiovascular, respiratory and physical parameters of health (BMI, muscular strength, psychomotor skills, etc.) are most prevalent. Mechanisms that affect metabolism, circulation (BP, atherosclerosis) and behavioural or social tendencies are frequently cited. Figure 2 depicts a summary of evidence as expressed in empirical and hypothetical findings.
Empirical evidence
Endocrine system: The strongest evidence in both quality and quantity suggests yoga has a positive impact on hormone regulation. Salivary levels of cortisol have been measured and notably decreased in numerous reviews and trials [8,14,19,20]. Lowering cortisol is associated with decreasing perceived stress, decreasing anxiety, increasing feelings of well-being and improving pain management [21]. Enhanced serotonin production for erectile dysfunction [20], oxytocin released during visualization techniques to regulate bone mass [11] and higher levels of melatonin to improve immunity and sleep quality [12,22] are other potential effects of yoga practice.
Nervous system: An explanatory framework that attributes benefits of yoga through direct influence on the sympathetic and parasympathetic activity in the autonomic nervous system is common. Evidence suggests the respiratory effects of pranayama, visualization and calming techniques in dhyana as well as physical movement in asanas reduce sympathetic activation, increase levels of gamma-aminobutyric acid (GABA) [23], regulate the hypothalamicpituitary- adrenal (HPA) axis to improve outcomes in mood disorders [18], stress [24], well-being and provides an anxiolytic effect [22].
Physical health: Physical health includes cardiorespiratory fitness, kinesiology, and biomechanics including balance, flexibility and anthropometric characteristics. Yoga interventions to increase strength and balance have demonstrated a capacity to decrease falls and risk of injury in a geriatric population [25]. Exercise training effects in lowering resting heart rate, oxygen consumption rate, decrease in basal metabolic rate (BMR) and decreasing body mass index (BMI) and fat mass indicate preventative effects for cardiovascular disease, diabetes and obesity [8,12,14,17].
Metabolism: The metabolic effects of yoga have been most intensely studied for glycemic control. Evidence for improved glucose tolerance and insulin sensitivity suggests that regular asana practice may replace drug therapies in type 2 diabetics [14]. Measureable improvements of clinical significance after yoga intervention are noted in fasting plasma glucose (FPG) and postprandial plasma glucose (PPPG) [17,26,27]. Balaji et al. [21] note increased hepatic lipase and lipoprotein lipase at the cellular level affects the metabolism and subsequent increase in uptake of triglycerides by adipose tissues.
Circulatory system: The circulatory pathways of health-related outcomes include lowering blood pressure and improving arterial function. Three authors discuss the potential circulatory benefits that include: lowering blood pressure, enhancing cardiovagal function and slowing atherosclerosis to prevent cardiovascular disease [14] increasing blood flow with the prompting of visual techniques [11] and restoring baroreceptor sensitivity [10].
Behavioural/social: A decrease in food consumption, eating speed and positive food choices following a yoga treatment program is shown to be effective for binge eating [28]. Enhancing sleep quality to improve psychological well-being is noted in two studies [14,19]. Reducing social isolation, fostering networks that reinforce physical activity and self-care could lead to improved pain management [24] and healthier physical and psychological responses to stress [21].
Antioxidant: Oxidative stress results from an imbalance in the prooxdiant- antioxidant equilibrium and is associated with a number of diseases [29]. Numerous findings identify an increase in levels of total antioxidant status (TAS) and other naturally occurring antioxidants in human cells such as glutathione (GSH) and plasma vitamin E following yoga intervention [14,17,30]. Preventative and treatment effects for cardiovascular disease, cancer, arthritis, diabetes and Alzheimer’s have also been indicated in these research findings. One 3-month clinical trial with diabetic yoga practitioners achieved a 20% reduction in oxidative stress following long-term regular sessions [17].
Inflammation: Yoga’s effect on decreasing inflammatory markers is a recent addition to research. With a focus on pain management and effective treatment of depression, the partial role of reducing proinflammatory cytokines such as IL-6, interleukin-2, C-reactive protein is attributed to yoga’s capacity to stimulate the vagus nerve [18,21,26]. The vagus nerve in turn decreases heart rate, blood pressure or both to improve responses to stress and which may have further effects on decreasing obesity and improving immunity [31].
Psychology and cognition: In two articles, increased feelings of satisfaction, self-confidence and self-control are linked to decreased perceived stress and increased well-being following yoga practice [14,20]. Another author states that “if yoga therapy offers an awareness of physical and mental states, benefits for pain management for back pain and cancer-related therapies including breast cancer may result [21]”, though the empirical evidence is insufficiently robust to confirm predictions.
Emerging Hypotheses
The following group of mechanisms belong to hypothetical areas of effect that depend on limited or indirect research for evidence.
Immunity
Two papers identify immunology for cancer treatment and stress reduction as a possible mediating factor and benefit of yoga practice [8,32]. Field [8] suggest yoga stimulates the vagal nerve that in turn reduces cortisol, the detriment of natural killers (NK) cells in the human body. This hypothesis was tested in women with breast cancer [33]. Results indicate that both lymphocytes and NK cells were increased following treatment and authors suggest the same effect may be triggered by yoga practice. Kulkarni et al. [32] propose further investigation ofx the molecular action on cellular, neuro-humoral and immune systems to reverse stress following yoga intervention.
Nerve conduction
For pain reduction, improved nerve conduction through ‘Gate theory stimulation’ and enhanced deep sleep to decrease ‘substance P’ as indicated through massage therapy may also demonstrate key benefits of yoga therapy [8], though empirical evidence is speculative.
Bioelectromagnetism
Various health effects and biological interactions are being explored through analysis of electrical and magnetic currents within our internal, cellular structures and external, environmental surroundings (i.e., low-frequency magnetic fields) [34]. As an effective agent to optimize health, delay age and treat various chronic illnesses, yoga’s pranayamic breathing and meditation may positively influence the transduction pathways, including bioelectromagnetism [35]. Empirical evidence to support this theory is not currently available.
Discussion
There are several published theories and hypotheses for yoga’s effect on health outcomes in healthcare databases. Some of these theories seek to inform biomedical perspectives including neurological and biochemical underpinnings, while some theories compare yoga to massage, or explore alternative concepts such as bioelectromagnetism. Consensus on the biological plausibility or causal pathways of how yoga might work is not indicated in this review. The degree of evidence to support the current hypotheses is relatively weak, and though 2000 yoga articles are published online, only 18 appear to be relevant to this research question and inclusion criteria. As a complementary therapy, yoga is becoming popular in both research and the wider community and it is important to address the fundamental questions regarding yoga’s impact on health outcomes. That is, not only does it work but if it does, how does it work?
Yoga as a complex intervention includes components with varying degrees of physical movement, mind-body exercises and in-depth philosophical teachings. Even though yoga literature emphasizes the psychological aspects of practice, current evidence focuses on conventional underlying effects of disease including hormone regulation and metabolism. Perhaps empirical study from new or integrated perspectives could include changes in behaviour or philosophical beliefs to increase the understanding and breadth of yoga as a health intervention. Some preliminary analysis of multiple yoga effects are offered in review papers [12,14], and will be helpful in evolving the discussion for causal pathways in disease-specific outcomes. A component-outcome analysis may also assist in improving evidence and dialogue.
Limitations of this review
The content of this review is largely limited by the quality and availability of publications in online health databases from three countries, the Netherlands (Scopus), United Kingdom (Cochrane Collaboration) and United States (PubMed). An in-depth search that includes other sources of information may yield different results. This search is current as of December 2012 and due to the pace of new research in this field, may be out of date by the time of publication. Still, the framework and rapid search offers an important structure to advance the quality and knowledge base for underlying mechanisms in yoga.
The author chooses to include clinical trials and reviews to increase the pool of evidence, though some low quality studies did not include adequate randomization may expose results to bias or confounding variables. As the purpose of this review is to summarize the potential underlying mechanisms of yoga therapy for health benefit, no conclusions should be drawn regarding the accuracy of hypotheses or efficacy of treatment for outcome effects.
Recommendations for future research
Previous authors state that immune function is underrepresented in yoga research [8] and the findings of this agree that immunology is a potential area for future consideration. In addition, oxidative stress, effects of behavioural, social and psychological experiences of yoga need to be better understood from a western medical point of view. The internal and external validity of future studies could be improved to address current worries of bias, limited generalizability and exposure to confounding variables. These methodological considerations should include the implementation of high-quality randomized controlled trials that measure disease-specific health outcomes, the use of well-defined characteristics of intervention and parallel testing of hypothetical underlying effects with components and specific outcome measures.
Conclusion
The effects of yoga on the endocrine system, nervous system, and physical health are documented with high frequency in the literature. The strongest empirical evidence suggests yoga’s capacity to regulate hormones which is a factor in providing health benefit, with a decrease of cortisol and increase of serotonin and melatonin levels following regular practice. Psychological, behavioural, religious or kinaesthetic effects of yoga seem deemphasized in the evidence. Emerging theories that warrant further investigation include biomarkers of immune function, oxidative stress and evidence for facilitating nerve conduction to relieve pain and stress. The extensive and varied components of yoga intervention (asana, pranayama, dhyana, philosophical teaching) indicate yoga is a complex intervention, therefore, to improve the clinical understanding of how yoga might work as a whole, empirical investigation into the components of yoga and testing of their specific outcomes is prospect for future study.
Acknowledgements
The author acknowledges Dr. Carl Heneghan and Dr. Alison Ward for their academic supervision and mentorship.
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