Several studies have examined the effects of yoga on physical fitness including flexibility, balance, spinal mobility and muscular endurance. Cognitive functions have also been assessed including executive function, attention, processing speed and memory.

After three months of yoga practice surface electromyographic signals during different poses suggested that downward facing dog poses are effective for strengthening abdominal muscles while chair and warrior one poses were strengthening the gluteus maximus muscles and all of these muscles could be strengthened by the upward facing dog pose.

After 10 weeks of yoga, a yoga group versus a nonyoga group of athletes showed increased flexibility and balance during different yoga poses including downward dog, upward dog, right foot lunge and the chair pose.

The Hatha yoga group featuring slow movements was more effective in improving flexibility than the fast movements in calisthenics.Yoga therapy

Cognitive functioning

At least one randomized controlled study, one systematic review and one meta-analysis have been conducted on the effects of yoga on cognitive functions including executive function, attention, processing speed and memory. In a randomized controlled study a Hatha yoga group was compared to a stretchingestrengthening comparison control group following an eight week period of 1 h classes three times per week. The yoga group showed significantly greater improvement on the executive function measures of working memory, shorter reaction times on switching trials and greater accuracy.

Prenatal yoga studies

Prenatal yoga has become increasingly popular and has raised questions regarding its safety and potential benefits on the pregnant women and their fetuses. The prenatal yoga studies reviewed here are focused on the intensity of yoga, the absence of physiological changes for the mother and the fetus during a number of poses (and therefore the safety of prenatal yoga), the beneficial effects on the mothers, and studies on alleviation of prenatal depression and anxiety and the resultant enhanced fetal growth, and the greater gestational age and birth weight of the newborn.

In a study examining the safety of prenatal yoga, maternal and fetal heart rate and temperature were taken during 26 different yoga poses. A comparison of the post session with the pre session data showed no change in pregnant women's heart rate, temperature or fetal heart rate and there were no falls or injuries during the total 650 poses. None of the participants reported fetal movement changes, contractions or vaginal bleeding, thus ensuring the safety of prenatal yoga even as late as 38 weeks gestation.

Turning to the beneficial effects of yoga on pregnant women, a systematic review of 10 randomized controlled trials suggested that those in the yoga groups had a lower incidence of prenatal disorders, lower levels of pain and stress, higher relationship scores and greater gestational age offspring. The reviewers also concluded that yoga was a more effective exercise than walking or standard prenatal exercises.

Perinatal depression reputedly affects approximately 20% of women and 10% of women are affected by perinatal anxiety. Because the literature is mixed on pharmacological treatment, depressed and anxious pregnant women are exploring alternatives including yoga. In a systematic review of the literature, 13 publications that met inclusion criteria suggested that yoga interventions reduced anxiety and depression. In a meta-analysis study six randomized controlled trials were identified, and the analysis involved comparison groups including prenatal care, exercise, social support and massage. Depression was significantly lower in the yoga versus the comparison groups. A surprising finding was that integrated yoga groups experienced a greater decrease in depression than the physicaleexerciseebased yoga groups, suggesting that the breathing and meditation components of yoga may add to the physical exercise of yoga poses. Even a single session of yoga has been noted to decrease state anxiety as well as cortisol levels in depressed pregnant women.

Up to 20% of women experience postpartum depression, in many cases a continuation of pre-natal depression. In a study in which postpartum depressed women were randomly assigned to a yoga or waitlist control group, 16 classes over eight weeks led to a greater decrease in postpartum depression and anxiety and an increase in quality of life. According to the authors,78% of the women in the yoga group experienced clinically significant change. In a study that provided Hatha yoga sessions (90 min) prenatally and assessed both prenatal and postpartum depression, the yoga group as opposed to the control group surprisingly experienced less depression during the postpartum but not the prenatal period.Yoga and cardiovascular system

Cardiovascular conditions

The recent literature on the use of yoga with cardiovascular conditions has focused on prehypertension, hypertension, and elevated cholesterol. High blood pressure is a notable risk factor for cardiovascular disease. •

Prehypertension

In a randomized controlled study, yoga, standard lifestyle modification and lifestyle plus yoga were compared for their effects on pre-hypertension (systolic BP 120-139 and/or diastolic BP 80-89). After three months of intervention the lifestyle plus yoga group showed a significant decrease in systolic blood pressure. In addition, 13 pre hypertensives became normotensive in the lifestyle plus yoga group as opposed to only four in the lifestyle group. In a study on mild hypertensives, a yoga group was compared to an active control group (nonaerobic exercise). The yoga group experienced a significant decrease in diastolic blood pressure, although the nonaerobic exercise group did not change. 

Hypertension and blood pressure

In a systematic review of randomized clinical trials 11 of 17 of the trials that met the inclusion criteria showed a significantly greater reduction in systolic and diastolic blood pressure as compared to pharmacotherapy, no treatment or usual care. The other six randomized controlled trials showed no significant yoga effects. In another systematic review and meta-analysis, yoga and exercise did not differ in their effects on systolic and diastolic blood pressure.

Cholesterol

Cholesterol altering yoga effects have also been prominent in this literature. In a randomized controlled trial attending a yoga program led to a significant increase in high density lipoprotein (HDL) as well as reduced blood pressure and glucose and an improvement in other lipid profile variables. Unfortunately, yoga was not compared to an active group and the yoga program included not only poses but also breathing exercises, meditation, group discussions and advice on stress management and healthy diet, confounding the question of yoga effects. However, when yoga was compared to a physiotherapy program, the yoga group showed significantly greater improvement in HDL, low density lipoprotein (LDL) and very low density lipoprotein (VLDL). In addition, unlike most other studies this research group also assessed stress, anxiety, depression and negative affect which were also more positively affected by yoga. When yoga was compared to exercise, a greater increase in HDL was noted in the yoga groups. This meta-analysis also showed improved systolic and diastolic blood pressure, heart rate, respiratory rate and waist circumference following yoga. In another systematic review and meta-analysis in which 37 RCTs were included, the yoga participants compared to non-exercise controls showed improved HDL, LDL, total cholesterol, triglycerides, systolic blood pressure and heart rate. These systematic reviews and meta-analyses, while suggestive, have limitations. They include a number of studies not adhering to inclusion criteria, small sample sizes and high attrition rates, highlighting the need for more robust randomized controlled trials.

Auto-immune conditions

Yoga has been used as a complementary treatment for several auto-immune conditions in recent studies. These auto-immune conditions include asthma, chronic obstructive pulmonary disease. Type II diabetes, multiple sclerosis, irritable bowel syndrome and chronic fatigue syndrome.

Asthma

Typically in the asthma studies forced vital capacity (FVC), peak expiratory flow rate (PEFR) and forced expiratory volume (FEV) have increased. In one of the asthma studies these measures increased in the short term and PEFR even increased at a 36 month follow-up following an 11 day hospital yoga program. In a systematic review and meta-analysis study on 14 randomized controlled trials, asthma symptoms, PEFR and FVC improved for the yoga groups as compared with usual care. When yoga was compared with psychological interventions there was a greater PEFR increase for the yoga group. Yoga has also shown better improvement on biochemical variables including a greater decrease in total leukocyte count in a randomized controlled study after six months of yoga.

Chronic obstructive pulmonary disease

In a systematic review and meta-analysis study on chronic obstructive pulmonary disease, five randomized controlled trials were included. These suggested that yoga significantly increased forced expiratory volume in 1 s and 6 min walking distance, suggesting improved lung function and exercise capacity.

Type II diabetes

Many yoga studies have been conducted with patients with type II diabetes mellitus. Typically the fasting and postprandial blood sugar have decreased following yoga. For example, in one study fasting and postprandial blood sugar decreased in both type II diabetes and normal volunteers after six months of yoga training. Another study showed a decrease in fasting and postprandial blood sugar as early as eight weeks of yoga. However, the yoga sessions included not only yoga poses but also breathing exercises and meditation, thus confounding the effects of the yoga poses. And, when yoga was compared to walking, no group differences were noted on fasting postprandial blood glucose, although the yoga group had lower weight, waist circumference and body mass index. In a systematic review on randomized controlled trials, 25 trials met criteria. These trials that included 2170 participants suggested improved glycemic control, lipid levels, oxidative stress, blood pressure and pulmonary and autonomic function. In addition there was a reduced need for medication and improved mood and sleep. Some have argued that these yoga effects on type II diabetes derive from parasympathetic activation and decreased stress including less HPA axis activation leading to better metabolic and psychological profiles, increased insulin sensitivity and improved glucose tolerance and lipid metabolism.

Multiple sclerosis

Multiple sclerosis (MS) is reputedly the most common autoimmune inflammatory disease of the central nervous system, affecting approximately 2.3 million people worldwide. The onset of the disease is typically at 20e40 years, there is a greater incidence in women, and individuals with MS experience several symptoms including fatigue, imbalance, spasticity, chronic pain, bladder and bowel dysfunction and cognitive, visual and speech impairments, depression, sensory disturbance and impaired mobility. Several studies have been conducted with multiple sclerosis. For example, in one study, after 12 weeks of biweekly yoga, significant improvement was noted in fatigue, balance, step length and walking speed. However, this study did not include a control group, treatment comparison or an active comparison group. Nonetheless, when yogawas compared, for example, to an aerobics group, the mean quality of life score was higher for the yoga versus the aerobics group. In a systematic review and meta-analysis, seven randomized controlled trials comparing yoga with usual care showed greater improvement for the yoga group on fatigue and mood. However, no short or long-term effects of yoga were noted when yoga was compared to exercise. When yoga was compared to walking, both conditions yielded similar reductions in total mood disturbance scores. When treadmill walking was compared to yoga, however, yoga had greater effects on reaction time during a cognitive task. When the effectiveness of individual versus group sessions were compared there was no significant difference between the conditions on fatigue scores.

Irritable bowel syndrome

Irritable bowel syndrome is the most common gastrointestinal disorder. In this six week twice per week Iyengar yoga study individuals with irritable bowel syndrome were compared with a waitlist control group. The attrition for this study was 24% and the attendance averaged 75%. The yoga group had a significant reduction in bowel syndrome symptoms including pain, constipation and nausea and the symptom reduction was maintained at the two month follow-up assessment. In a comparison between 16- biweekly sessions of Iyengar yoga and walking, positive effects were noted for both groups. Irritable bowel syndrome severity symptoms decreased for the yoga group, while overall G.I. symptoms decreased for the walking group. However, at a six month follow-up the walking group continued to benefit, while the yoga group showed no sustained improvement, probably because the walking group reported walking more often than the yoga group practiced yoga.

Chronic fatigue syndrome

Yoga has also been effective for patients with chronic fatigue syndrome in at least one study. In this study, fatigue scores decreased for the yoga versus the waitlist control group following biweekly 20 min sessions with the yoga instructor as well as daily in-home sessions for approximately two months.

Cancer and yoga

The yoga for cancer data are also inconclusive. Regarding pediatric cancer, one group of researchers had difficulty recruiting children and adolescents (32% enrollment), although attendance at the 6-week program was excellent (90%). After the six week program the children had a significant decrease in anxiety scores. In the other recent study on pediatric cancer the recruitment, retention and attendance rates were good for a 12 week yoga program (two times per week). The children showed an increase in quality of life, functional mobility, hamstring flexibility and physical activity levels at the end of the program. Both of these studies were repeated measures within subjects studies as opposed to randomized controlled trials, suggesting very tentative results.

Breast cancer

The lion's share of the recent yoga for cancer research has been conducted on breast cancer. In a randomized controlled trial comparing yoga and usual care, fatigue was reduced and in a similar trial, musculoskeletal pain was reduced. These trials were limited given that the yoga poses were combined with breathing exercises and meditation, as in many of the other randomized controlled trials. The same confound occurred in a yoga versus exercise study in which the yoga group showed greater physical activity and less sleep disturbance. In another yoga versus exercise study no group differences were noted on decreased body fat. In a yoga versus a stretching versus a waitlist control group, at the end of the six treatments the yoga group showed the greatest reduction in depressive symptoms and sleep problems. And in another yoga versus stretching versus waitlist control group study, at the end of the six week treatment period (3 times a week) and at a six month follow-up period the yoga group showed greater increases in physical functioning and greater decreases in cortisol levels.

Yoga and Breast CancerHowever, when yoga was compared to an aerobics exercise program (30 min a week for six weeks) similar effects were noted for both groups. These included increased muscle strength and performance on the 6 min walk test. Yoga has also been noted to decrease lymphedema in the upper extremities of women with breast cancer. This decreased arm volume was significant but the sample was small and this was a pre-posttest design without a control group. In another study that was a randomized controlled trial for yoga (again for 8 weeks), the yoga group had a greater decrease in tissue induration of the affected upper arm but there was no difference in arm volume/lymphedema. Further, at a four week follow-up period there were no longer any positive effects. This sample, however, was also small, highlighting the need for further arm volume studies. Both increased pro-inflammatoryerelated genes and increased antiinflammatory related genes have resulted from a 12-week Iyengar yoga versus a health education control condition which could explain the mixed results just described. Yoga, by virtue of its sustained high energy poses, and the rest periods in between, could result in mixed effects depending on the ratio of rigor to rest.

Colorectal cancer

The only other cancer publications during this recent period included a study on colorectal cancer in which fewer sleep disturbances were noted following the end of the yoga intervention (90 min once weekly for 10 weeks) suggesting long-term effects. However, this study featured high attrition and low adherence. Another miscellaneous study on cancer featured laughter yoga (thought to massage the internal organs) which was noted to decrease stress from chemotherapy. And, finally a survey was conducted about oncologists recommending yoga to their cancer patients. Only a small number of the respondents recommended yoga, claiming that more research was needed to document positive effects of yoga.