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Journal of Complementary and

Integrative Medicine

Volume 6, Issue 1 2009 Article 15

Using the Biopsychosocial Model to

Understand the Health Benefits of Yoga

Subhadra Evans Jennie CI Tsao

Beth Sternlieb Lonnie K. Zeltzer

University of California, Los Angeles, [email protected]

University of California, Los Angeles, [email protected] of California, Los Angeles, [email protected]

University of California, Los Angeles, [email protected]

Copyright c2009 The Berkeley Electronic Press. All rights reserved.


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Using the Biopsychosocial Model to

Understand the Health Benefits of Yoga

Subhadra Evans, Jennie CI Tsao, Beth Sternlieb, and Lonnie K. Zeltzer

Abstract

Yoga is widely practiced as a means to promote physical, psychological and spiritual well-

being. While a number of studies have documented the efficacy of yoga for functioning in healthy

individuals and those experiencing illness or pain, biopsychosocial effects have not been detailed.We propose an analogue between the physical, psychological and spiritual effects of practice as

espoused in yoga traditions, and the biopsychosocial model of health. To this end, we present a

review and conceptual model of the potential biopsychosocial benefits of yoga, which may provide

clues regarding the possible mechanisms of action of yoga upon well-being. Physical systems acti-

vated through yoga practice include musculoskeletal, cardiopulmonary, autonomic nervous system

and endocrine functioning. Psychological benefits include enhanced coping, self-efficacy and pos-

itive mood. Spiritual mechanisms that can be understood within a Western medical model include

acceptance and mindful awareness. We present empirical evidence that supports the involvement

of these domains. However, additional well-conducted research is required to further establish the

efficacy of yoga for health states, and to understand how posture, breath and meditative activity

affect the body, mind and spirit.

KEYWORDS: yoga, health, biopsychosocial

This report was supported in part by The Sue Stiles Foundation for Integrative Oncology (PI:

Lonnie K. Zeltzer).


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Introduction

Yoga is an ancient tradition practiced to promote the well-being of body, mind

and spirit. The beneficial effects of yoga are believed to occur through asana(poses), pranayama (breath) and dhyana (meditation) and traditionally, yama

(ethical behavior), niyama (self discipline), pratyahara (sense withdrawal),dharana (concentration) and samadhi (deep meditative awareness). Today, yoga is

widely used as a means of exercise and relaxation. Despite the ancient origins of

yoga as a spiritual and metaphysical practice, the medical use of yoga to promote

physical fitness and ameliorate physical complaints may only have gainedprominence in the last century, both in India and abroad (Alter, 2004). It is

therefore important to understand the contemporary use of yoga for medical

purposes, including the development of a model that incorporates a broad range ofeffects upon health. The purpose of this paper is to provide an overview of the

biopsychosocial benefits of yoga, including directions for future research in whichmechanisms of action can be further explored.

Recent surveys point to the ever-increasing popularity of yoga in

alleviating pain, stress and illness. Estimates suggest that approximately 5% of

adults in the US practice yoga (Barnes, 2004). A recent study of complementary

and alternative medicine (CAM) preferences among children at a tertiary painclinic found yoga to be amongst the three most popular treatments (Tsao, 2007).

Despite its popularity, limited research has explored the empirical efficacy of

yoga. Even in studies that have addressed yogas effectiveness, the larger questionof how yoga works remains outstanding. To date, mechanisms behind the

therapeutic effects of yoga remain unclear and a systematic model for

understanding levels of action on the entire person has not been offered in themedical community.

The intention of this paper is to understand the relationship between yogaused for healthful purposes and the biopsychosocial model of healthcare which

explains mind/body relationships in pain, stress and illness. Rather than providing

a systematic review of the efficacy of yoga for a single aspect of health, a numberof which already exist for cancer, pain and psychological functioning (Bower et

al., 2005; Evans, 2008; Kirkwood et al., 2005; Monro, 1995; Pilkington et al.,

2005), we offer a model conceptualizing a range of biopsychosocial benefits,

which may together impact well-being. We believe the use of such a model isintegral in establishing the direction of future yoga research. In order to promote

the understanding and ultimate use of CAM therapies within conventional health-care settings, mechanisms of action should be charted by considering benefitsacross functioning, including biological, psychosocial and spiritual aspects of

well-being. To this end, we present such a conceptual model of yoga on health

outcomes (see Figure 1) that can be integrated into current medical science.

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Evans et al.: Action of Yoga on Health

Published by The Berkeley Electronic Press, 2009


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Databases that were searched included PubMed, PsycINFO and CINAHL;

yoga studies referenced in published papers were cross-referenced, and any

studies not in databases, but mentioned in papers were included where possible.

Pilot studies, randomized controlled trails (RCTs), controlled trials and single-armrepeated-measure designs which examined the biopsychosocial impact of yoga on

health, illness or pain were reviewed. Keywords used in the literature searchincluded yoga, mindful, health, pain, illness, disease, psychology, spiritual,

quality of life, mechanisms, and biopsychosocial.

Applying the Biopsychosocial Model to Yoga

Yoga currently consists of numerous traditions, and while most incorporate

posture, breath and meditation, they can vary greatly in execution and focus. Webriefly consider two popular styles practiced within the US to illustrate such

differences. Iyengar yoga is frequently used in studies of yoga for chronic painand emphasizes alignment, holding postures for periods of time, and sequencingof postures. The practice is typically individualized to a students ability, motility,

and health needs through the use of props and uses specific therapeutic sequences

for students with health problems. An extensive teacher training program ensures

replication of poses and sequences (Mehta, 2006). Ashtanga Yoga involvessynchronizing the breath with a progressive series of postures and the emphasis is

on an energetic flow of postures, which are often executed and repeated in quick

succession. The use of breath and quick progression of poses is designed toproduce internal heat and improved circulation and strength (Haaz, 2007).

The ultimate goal of these traditions is to achieve mental, spiritual and

physical well-being by establishing balance within the internal and externalenvironment (Taimni, 1961). This goal, when applied to the promotion of health,

is compatible with the goal of Western medicine: to establish homeostasis in thebody. Current conceptions of health use the biopsychosocial model, which

addresses a persons physiology, psychology, environment and behavior to

understand how social and psychological factors interact with biology to influencepain, illness and health (Gatchel et al., 2007). The purported action of yoga on

well-being is possible when considered from a biopsychosocial model, whereby

an individuals mind, body and wider social environment all impact health states.

In some diseases, such as rheumatoid arthritis, psychosocial factors includingstress and lifestyle choices may explain as much as 20% of a patients disability

(Drossaers-Bakker et al., 1999; Escalante & del Rincon, 1999). The combinationof body, mind and breath awareness used in yoga is likely to have acorresponding impact on psychophysiological functioning. Indeed, as explored

below, yoga appears to produce homeostasis across multiple aspects of an

individuals functioning and physiology.

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Journal of Complementary and Integrative Medicine, Vol. 6 [2009], Iss. 1, Art. 15

http://www.bepress.com/jcim/vol6/iss1/15

DOI: 10.2202/1553-3840.1183


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Figure 1. Conceptual Model of the Biopsychosocial Benefits of Yog

PsychosocSelf-efficac

Coping

Social suppPositive Mo

SpiritualCompassionate understanding

Mindfulness

Yoga

Structural/PhysiologicalMusculoskeletal functioningCardiopulmonary status

ANS responseEndocrine control system

Enhanced FunctioningEnergy & sleepQuality of Life

Strength & fitnessReduced pain, stress & disability




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Biopsychosocial Benefits of Yoga

Scientists have long recognized the healthful benefits of exercise, especially for

disease, illness and pain states. Exercise, fitness, and musculoskeletal andcardiopulmonary functioning are intimately connected. Physical activity has also

increasingly been linked to improved mood (Greenwood & Fleshner, 2008). Inaddition to positive effects on structural and psychophysical outcomes, exercise

likely impacts brain chemistry to regulate somatomotor-sympathetic circuits

(Kerman, 2008).

We propose that yoga shares many of the physical and psychologicalbenefits of exercise, in addition to specific effects not shared by regular exercise.

In yoga, the practice of not seeking the fruit of actions, but to practice for its own

sake (Mehta, 2006) is in contrast to many forms of physical activity, which oftenrely upon a comparison to others or pushing oneself beyond limits to define

progress. The non-competitive focus on personal development cultivated by yogais believed to pave the way for psycho-spiritual achievements such ascompassionate understanding, or acceptance, and mindful awareness. Other

achievements that have been suggested to follow yoga, but not other forms of

physical activity, pertain to physiological functioning - including control over

bodily systems. Maintaining postures is thought to lead to strengthening andrelaxation of voluntary muscles and eventually to control over the autonomic

nervous system (ANS) (Vahia et al., 1966). Preliminary support for this notion

exists in research demonstrating voluntary control over heart rate after a 30 dayyoga intervention (Telles et al., 2004). Empirical evidence for the biological and

psycho-spiritual benefits of yoga is further discussed below, and while some

findings are similar to those seen for regular exercise, other benefits such as ANScontrol and increased mindfulness appear to be specific to yoga.

Structural/physiological benefits: It is thought that yoga quiets the body as well

as the mind through vascular and muscular relaxation (Monro, 1995). Empirical

research demonstrates support for this view, as yoga has been associated withbenefits across a number of physiological systems. From a basic physical activity

perspective, yoga may be particularly suited to people with chronic health

conditions. When practiced correctly, yoga is unlikely to irritate inflammation,

and yet involves movement to improve strength (Greendale et al., 2002; Haslocket al., 1994), flexibility (Greendale et al., 2002) and range of motion, along with

attention to alignment (DiBenedetto et al., 2005; Garfinkel et al., 1994).While more static yoga poses may only possess the metabolic cost of light

intensity exercise (Clay et al., 2005), other findings have indicated that intensive

poses or sequences, such as surya namaskar (performed for longer than 10

minutes), are in fact associated with sufficiently elevated metabolic and heart rate

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responses to improve cardio-respiratory fitness (Hagins et al., 2007). In a RCT of

40 healthy 12-15 year-old boys randomly assigned to a yoga intervention for one

year, significant improvements were found in body weight, cardiovascular

endurance and anaerobic power compared to usual activity controls (Bera &Rajapurkar, 1993). A recent repeated-measures study suggested that practice of

surya namaskar represents a promising form of aerobic exercise as it involvesstatic stretching as well as a slow, dynamic component of exercise with optimal

stress on the cardiorespiratory system (Sinha et al., 2004). Another study

examining a 6-week yoga practice for 20 adolescents found that yoga had an

effect on the bodys glycolytic enzymes similar to endurance training (Pansare, etal., 1989). Others have reported the positive impact of yoga on metabolic

outcomes, including cholesterol and fasting plasma glucose (Bijlani et al., 2005),

as well as a significant reduction in girth circumference (Khatri et al., 2007).However, a number of studies did not include control groups (Bijlani et al., 2005;

Pansare et al., 1989; Sinha et al., 2004) and further research is required toestablish the metabolic cost of energetic versus less energetic forms of yoga.

A number of findings point to the musculoskeletal and cardiopulmonarybenefits of yoga. It has been argued that the extension and flexion of muscles

during yoga poses is associated with activation of antagonistic neuromuscular

systems as well as tendon-organ feedback resulting in increased range of motionand relaxation (Riley, 2004). Yoga interventions for individuals with arthritis and

other musculoskeletal conditions have found improvement in a range of physical

outcomes, including pain, strength, joint tenderness, range of motion anddisability (Evans, 2008). The cardiopulmonary effects of yoga have also been

studied. Consistent with yoga theory that the cells of the body represent pearls of

life and that yoga practice supplies ample fresh blood and energy to each cell(Mehta, 2006), a study focusing on mechanisms of action found that slow

breathing techniques used during yoga were associated with increased oxygendelivery to tissues in 10 yogis compared to 12 controls with no yoga experience

(Spicuzza et al., 2000). A study comparing the pulmonary functioning of 60

athletes, yogis and sedentary controls found similar lung functions for the yogisand athletes, which were significantly enhanced compared to the controls

(Prakash et al., 2007). As discussed below, yoga practice has also been associated

with improved respiration and heart rate variability measures. A recent review

concluded that yoga has cardiopulmonary benefits for healthy individuals andpossibly those with musculoskeletal and cardiopulmonary conditions (Raub,

2002). In this review, likely physiological mechanisms were identified, includingincreased skeletal muscle oxidative capacity, decreased use of glycogen and slowincrease in lung capacity. Empirical research is required to further test these

mechanisms.

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Studies linking yoga with autonomic nervous system (ANS) functioning

have found reduced stress responses, including blood pressure, heart rate, and

respiration (Bharshankar et al., 2003; Granath et al., 2006; McCaffrey et al., 2005;

Sarang, 2006), especially for illness states such as coronary artery disease(Sivasankaran et al., 2006) and hypertension (McCaffrey et al., 2005). In addition,

a 10-week course of yoga for patients with refractory epilepsy found enhancedparasympathetic activity and a decrease in seizure frequency following yoga in a

group of 18 patients compared to 16 exercise control patients (Sathyaprabha et al.,

2008). A recent study reported that heart rate variability (HRV), a measure of

cardiac autonomic activity, increased in a group of 11 yogis following a class ofIyengar yoga compared to a placebo session and a group of regular activity

controls (Khattab et al., 2007). An increase in HRV parameters is consistent with

healthy functioning and a reduced risk of heart disease. Monitoring breath duringyoga may be especially relevant for ANS functioning. Voluntary control of breath

has been associated with increased HRV (Lehrer et al., 1999), and it is possiblethat breath awareness during yoga may produce autonomic control similar to thatseen during biofeedback. This research provides preliminary support for the

positive effects of yoga on regulation of arousal systems.

Yoga may have differential short-term versus long-term effects on the

ANS. During active poses, heart rate and respiration may increase consistent withphysical activity (Sinha et al., 2004). However, during and following savasana,

the restful meditative pose that concludes most yoga classes, parasympathetic

activity consistent with relaxation and a reduction in physiological arousal isapparent (Sarang, 2006). Yoga practice also appears to result in increased control

over ANS responses such as heart rate. For example, after a month of yoga

practice, a group of 12 healthy participants had a lower resting heart rate after theintervention compared to a matched group of 12 regular activity controls; the

yoga group was also able to significantly lower their heart rates when giveninstruction to do so (Telles et al., 2004). Although larger RCTs are required to

replicate these findings, the study suggests physiological benefits of yoga

consistent with regular exercise in the form of lower resting heart rate, in additionto yoga-specific psychophysiological control. It is also possible that different

systems of yoga produce differential effects on the ANS. Fast moving yoga poses

as seen in Ashtanga yoga may lead to short-term physiological arousal, whereas

restorative practices commonly cultivated in Iyengar yoga may be associated withshort- and long-term parasympathetic nervous system dominance. Further

research is needed to elucidate the specific and differential activity of the ANSduring and following various traditions of yoga.

Yoga also appears to impact the endocrine system. It is hypothesized that

asana practice massages the internal organs, resulting in enhanced blood

circulation, glandular functioning and ultimately the balance of hormone

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production (Monro, 1995). Specific poses, such as savasana, may modulate brain

chemistry, particularly the hypothalamus (Bose et al., 1987), which links the

nervous and endocrine systems and is involved in the action of stress hormones.

Empirical studies examining neuroendocrine changes following yoga havegenerally focused on cortisol, a measure of stress response system activation.

Most studies have reported a reduction in cortisol with yoga practice (Kamei etal., 2000; Vedamurthachar et al., 2006; West et al., 2004). Although these results

are compelling and suggest a lowered stress response following yoga, only one

study used a randomized controlled design (Vedamurthachar et al., 2006). This

studys exclusive use of participants with alcohol dependence and SudarshanKriya Yoga, a practice of yoga focusing on breath rather than posture, also limits

generalizability. Increase in nighttime plasma melatonin, a hormone associated

with sleep quality, has been reported following yoga in a small group ofexperienced meditators (Tooley et al., 2000) as well as in 30 healthy men aged

25-35 years randomized to a 3 month exercise control group or a yogaintervention (Harinath et al., 2004). These findings provide support for a possiblemechanism linking sleep quality and yoga (Khalsa, 2004) and lend preliminary

credence to yoga theory maintaining that yoga practice enhances and normalizes

endocrine function. Further scientific studies are required to understand the full

range of endocrine functions that may be impacted by yoga.

Psychological benefits: Yoga has a number of positive effects on psychosocial

functioning which have been reported in healthy, pain and stressed individualsspanning a wide age-range. Psychological effects include increased self-efficacy,

coping, social support and positive mood. In a healthy group of 194 participants

enrolled in a 3 month community-based yoga program, significant pre-postimprovements on depression, anxiety and self-efficacy scales were reported (Lee

et al., 2004). In a group of 12 caregivers to older dementia patients, a six-weekpractice of yoga and meditation revealed significant pre-post improvements in

depression, anxiety and self-efficacy (Waelde et al., 2004). An RCT of

adolescents with irritable bowel syndrome was found to reduce anxiety andadaptive coping following four weeks of yoga home-practice compared to wait-

list controls (Kuttner et al., 2006). An RCT examining yoga (unspecified

tradition) for headache also reported improved coping and headache symptoms

after a 4-month treatment of yoga compared to standard treatment controls(Kaliappan, 1992). In another RCT, Woolery et al, (2004) reported reduced

depression and anxiety after a 5-week Iyengar yoga practice in mildly depressedyoung adults compared to waitlist controls. A recent single-group outcome studyfound reduced depression, anger, anxiety, and neurotic symptoms in 17 patients

with unipolar major depression in partial remission who completed an Iyengar

Yoga intervention (Shapiro, 2007). Reductions in low frequency heart rate

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variability were also evident post intervention, indicating a biological reduction in

stress responsivity.

Yoga has also been linked to social benefits, consistent with the notion

that exercise performed in a group can promote social well-being, which in turn isimportant for functional status in chronic disease (Weinberger et al., 1990). Yoga

classes have been associated with social benefits in a range of populations,including a RCT of yoga for a multiethnic group of breast cancer survivors

(Moadel et al., 2007), general cancer patients (DiStasio, 2008), and a pilot study

treating osteoarthritis of the knees (Kolasinski et al., 2005).

Two reviews examining yoga for depression and anxiety have underscoredthe promise of yoga for improving mood. Out of five RCTs of yoga for

depression, beneficial effects were reported in four (Kirkwood et al., 2005). All

eight randomized studies of yoga for clinical anxiety disorders reported areduction in symptoms following yoga (Pilkington et al., 2005). Findings did not

appear to vary as a function of symptom severity, suggesting that benefits may beavailable to individuals with mild depressive symptoms and anxiety through toclinical level symptomology. It has been argued that increased mastery of poses,

emotional release, tolerance of vulnerability related to opening of the body

posture, and a sense of relaxation in restorative poses all contribute to the positive

effects of yoga on mood (Woolery et al., 2004).The mood enhancing effects of yoga could arise from a number of

sources. Similar to exercise, yoga may have biochemical benefits that are related

to psychological functioning, as well as provide resources for coping and self-esteem which impact psychological well-being. A recent study found a 27%

increase in the neurotransmitter GABA, low levels of which have been linked to

mood disorders, in a group of 8 yoga practitioners compared to 11 controls whospent time reading (Streeter et al., 2007). These findings point to possible

biochemical mediators in the effect of yoga on functioning.Consistent with the biopsychosocial model, positive psychological

functioning is likely to lead to improved physical functioning, especially in

patients experiencing chronic pain and illness. For example, positive coping,including higher pain control and rational thinking, have been linked to improved

pain scores in young rheumatoid arthritis patients (Schanberg et al., 1997).

Health-related self-efficacy, or the tendency to persist in health behaviors despite

obstacles, has also been related to decreased pain behavior (Buckelew et al.,1994) and fewer somatic symptoms in chronic pain patients (Bursch et al., 2006).

The observed improvements in mood, adaptive coping, social support and self-efficacy following yoga suggest that the healthful effects of yoga may at leastpartially be mediated by enhanced psychological functioning.

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Spiritual benefits: Related to the psychological benefits of yoga are the spiritual

underpinnings of yoga. Spirituality has emerged as a core domain in quality of life

assessments in patient populations, including oncology patients (Whitford et al.,

2008), and is increasingly considered an integral part of health (McBrien, 2006).Working definitions of spirituality include a system of beliefs or values (which

can be religious or not), life meaning, purpose and connection with others or atranscendental phenomena (Sessanna et al., 2007). Yoga practice involves a

system of beliefs, values, life meaning and a connection with others that can be

practiced either as a religious path or secularly. We explore two such spiritual

contributions of yoga: compassionate understanding, oracceptance, and mindful

awareness. It is worth noting that in Western science, concepts such as

acceptance and mindfulness may overlap with psychological functioning and are

often accepted within mainstream psychology, such as in Acceptance andCommitment Therapy (ACT; Fletcher & Hayes, 2005).

A guiding principle of yoga is to foster the resilience to work with, oraccept, negative forces in life (Raub, 2002). An individual with debilitated healthwould be encouraged to accept his or her limitations, yet continue to pursue a full

practice of yoga, using props to support poses and ultimately to complete life

tasks despite physical challenges. Yoga can therefore be associated with the

development of skills in mastering difficulties in life, which may extend todealing with suffering and pain (Raub, 2002). Regular practice of yoga may act to

redefine an individuals experience of pain or difficulty, encouraging acceptance

of pain, and the continuation of functioning despite pain (Iyengar, 2005). Thisnotion is compatible with Western medicine, where acceptance of pain is viewed

as important for those with chronic conditions to persist in regular activity (Mason

et al., 2008). In a study examining the effects of yoga on healthy women,measures of life satisfaction increased while other personality variables including

excitability, aggressiveness and somatization decreased in a group of 25 womenpracticing yoga compared to a control group of 13 women who read in a relaxed

position for the same duration (Schell et al., 1994). These findings point to a

possible reorientation in understanding or acceptance of oneself through yoga.Further research is required to elucidate whether yoga allows individuals with

medical conditions to reach a level of acceptance or peace regarding their health

status, abilities and limitations.

Although untested, a possible derivative of acceptance through yoga is acorresponding ability to see benefit within hardship. Benefit finding, or the

tendency to look on the bright side in the face of hardship is being studied inpatient populations within health psychology. Women with breast cancer oftenreport personal or social development resulting from the experience (Sears et al.,

2003), which when used in expressive writing, is associated with reduced physical

symptom reports and fewer medical appointments compared to writing about facts

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(Low et al., 2006). It is possible that compassionate understanding towards

oneself and others fostered through yoga would facilitate an increase in such

benefit finding. Future research examining yoga for medical conditions should

include measures of acceptance and benefit finding.Yoga is also associated with mindful awareness, a concept that has been

integrated in empirically validated approaches including cognitive-behavioraltherapy (Brown & Ryan, 2003). Mindfulness is an openness or receptive

awareness to what is occurring in the present. Meditation and yoga are thought to

modify the influence of stress on the mind by strengthening attention or

mindfulness (Monro, 1995). Mindful activity through yoga has been found toimprove mood and stress (Netz & Lidor, 2003). In this study, 147 female teachers

enrolled in yoga, Feldenkrais (awareness through movement), dance or swimming

class, and a computer class served as the control group. Mood improvement wasevident only in the yoga, Feldenkrais and swimming groups, leading the authors

to suggest that mindfulness in activity plays a role in benefit. Yoga generallyinvolves mindful techniques, particularly in relation to ones breath and thephysical body, including posture, balance and symmetry. This focus on body,

mind and breath in the present moment can then free attention to explore ways of

minimizing stress, disability and pain. Understanding of the body is thought to

lead to healthy lifestyle choices and control over physiological systems (Khalsa,2003). Empirical evidence for this notion exists. Heightened attention to

alignment has been reported following yoga in a single arm study of 21 patients

with hyperkyphosis (Greendale et al., 2002). Mindful awareness has further beenassociated with a range of positive health outcomes, including improvements in

stress, reductions in cortisol levels, production of pro-inflammatory cytokines

consistent with immune enhancement as well as lowering of blood pressure/heartrate in cancer patients (Carlson et al., 2007).

Enhanced Health Outcomes Following Yoga

Multiple research studies have documented the health benefits of yoga, withimprovements found across varied aspects of functioning. Recovery of energy

levels and sleep are apparent in individuals with chronic illness and stress (Bower,

unpublished manuscript; Oken et al., 2004; Telles et al., 2007; Yurtkuran et al.,

2007), those with insomnia (Khalsa, 2004) as well as healthy individuals (Booth-LaForce et al., 2007; Manjunath & Telles, 2005). Increased strength and fitness

have been reported for healthy individuals and those with chronic conditions(Dash & Telles, 2001; DiBenedetto et al., 2005; Garfinkel et al., 1998; Greendaleet al., 2002; Haslock et al., 1994). Reduced pain and disability and increased

quality of life have also been reported in RCTs for various conditions, including

migraine and headaches (John et al., 2007; Kaliappan, 1992), rheumatoid arthritis

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(Garfinkel et al., 1998), osteoarthritis (Garfinkel et al., 1994) and chronic low

back pain (Williams et al., 2005). Reviews of RCTs of yoga for health conditions,

including cancer (Bower et al., 2005), chronic pain (Evans, 2008), anxiety

(Kirkwood et al., 2005) and depression (Pilkington et al., 2005) have concludedthat yoga is a promising intervention. As also identified in these reviews, research

remains limited by a range of methodological issues, including small samplesizes, lack of randomization and control groups, blinding of assessors and use of

unvalidated tools. An additional problem limiting much of the literature is a lack

of clear description regarding yoga asanas, teacher training and yoga tradition

utilized. Despite these issues, the balance of evidence indicates that yogapromotes health-related functioning in healthy individuals and those experiencing

illness or pain.

Conclusions

The bulk of evidence indicates that yoga holds promise in acting favorably uponmultiple and widespread aspects of an individuals health. It seems scientifically

possible that through yoga, individuals can regulate their body, mind and spirit in

such a manner as to produce benefits in biological, psychosocial and spiritual

domains. Although we discussed separate effects on physiological, psychosocialand spiritual systems, in reality, yoga is likely to affect multiple systems

simultaneously. For example, changes in brain chemistry such as GABA levels

and stress hormones such as cortisol may be associated with reductions indepressive or anxious symptoms and enhanced physiological functioning.

Likewise, increased mindful awareness may promote coping within the

psychological domain, providing a psychospiritual mechanism for enhanced well-being.

For the most part, we have limited knowledge of how various systems ofyoga work. Many traditions of yoga exist, but not all published studies document

the tradition employed or provide detailed descriptions of poses used. This lack of

information is perhaps one of the more substantial concerns regarding the currentstandard of yoga research. Without detailed information regarding yoga

interventions, replication of findings and an understanding of action on the body

and mind is limited. Different traditions of yoga have been likened to different

forms of psychotherapy such as cognitive behavioral, interpersonal andpsychodynamic approaches (Bower et al., 2005). In this sense, not all forms of

yoga are interchangeable and some traditions may vary widely in emphasis andapproach. This variation may be especially problematic when documenting thephysiological and in particular, the metabolic effect of yoga on the body. While

some traditions such as Iyengar yoga focus on postural alignment and awareness,

a tradition that would theoretically benefit the musculoskeletal and

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parasympathetic systems, other traditions such as Ashtanga yoga stress an

energetic flow of postures likely associated with short-term autonomic and

metabolic activity similar to that seen in other forms of moderate physical

activity. Given the possible differential action of these styles of yoga, it is notsurprising that conflicting findings exist regarding the physiological effects of

yoga practice, particularly the metabolic cost of yoga activity (Clay et al., 2005;Hagins et al., 2007). Future research is required to understand the action of

specific styles of yoga, at which point interventions could be designed for specific

populations. For example, Iyengar yoga appears to be particularly beneficial for

patients with musculoskeletal conditions (Evans, 2008).An additional note regarding the design of yoga interventions concerns

potential risk and safety issues. While there is likely to be only minimal risk of

adverse events when teachers are sufficiently trained and experienced in workingwith the population studied, risk of complications is magnified when teachers are

not carefully selected. This is particularly the case when working with patientpopulations who have specific physical and psychological limitations.Interventions with patients require careful assessment and selection of poses and

breathing exercises that are part of a clear yogic tradition, and which involve a

lineage of teachers to ensure maximal effects for patients and minimization of risk

and injury. It is therefore recommended that researchers work with experiencedand trained yoga teachers who have in-depth knowledge of the population they

are working with. Any publications generated from this research should also

include a clear description of poses used, training undertaken by teachers and thetradition of yoga employed.

We have explored a number of key benefits underlying the relationship

between yoga practice and well-being. However, the empirical evidence remainslimited, primarily in methodological design, including small sample sizes, lack of

control groups, lack of randomization, and unclear description of what constitutedthe experimental period or number of sessions. An over-reliance on uncontrolled

and non-randomized designs prevents conclusions about the contribution of yoga

independent of confounding variables. In addition, much of the empirical yogaliterature has emerged from India, and it is unclear to what extent the findings are

generalizable to populations in the US and other industrialized countries.

Similarly, it is unclear whether research conducted outside India is representative

of yoga as it is practiced and known in India.Further research into mechanisms of action is also required. Facilitated

dialogue between those versed in yoga and Western medicine and research willenable greater understanding of how yoga may promote health. A number ofbenefits are expressed in yoga texts, but have yet to be studied scientifically. For

example, many purported benefits relate to the action of particular poses,

including lymphatic circulation through inversions and modulation of the adrenals

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which can be stimulated through backbends and pacified in forward bends

(Iyengar, 1966; Iyengar, 2001). However, research has yet to document the effects

of specific poses on corresponding physiological systems. The action of

inversions on the adrenal system, for example, requires empirical validation.Future research should attempt to integrate yoga theory and the biopsychosocial

theory within highly rigorous and well-conducted research studies.Future empirical studies of yoga should incorporate the same stringent

research standards as those used in psychological and medical science. Thus,

well-designed large RCTs of yoga need to describe attrition rates and adherence

in class and home practice, establish intervention details such as total duration,number of sessions per week and length of each session, and the dose required for

benefit. The selection and description of appropriate control groups is also

necessary. Developing a legitimate sham yoga group has practical and ethicalchallenges and most RCTs have used a standard care control group. After initial

studies have documented the feasibility, safety and preliminary efficacy of yogafor particular conditions, control groups need to account for possible placeboeffects related to patient expectations, the social benefits of being in a class and

attention from the group facilitator. Although blinding of participants to group

status is difficult, ensuring experimenters and raters are unaware of group

assignment is necessary. As discussed, additional considerations includeidentification of the yoga tradition studied, and specification of teacher training

and poses used.

Yoga is a holistic practice impacting well-being through various systemsin a seemingly complex yet integrated manner. Although individual aspects of

yoga may prove interesting to study, it is possible that the benefit of yoga is

greater than the sum of its physical, psychological and meditative parts.Attempting to reduce benefits to simply stretching limbs, or relaxation techniques

may undermine yoga as a complete system for operating on multiple aspects ofthe person to achieve health and well-being. Moving forward, yoga research

should incorporate biological, psychosocial and spiritual outcomes if we are to

understand the therapeutic benefits of yoga for medical and healthy populations.

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