Abstract
Objectives:
Yoga is a popular form of exercise in the Western world, and yoga's effects on pulmonary function have been investigated previously. The purpose of this article is to review this research systematically and determine if regular yoga training improves pulmonary function in apparently healthy individuals.
Methods:
Using the Alternative Health Watch, the Physical Education Index, Medline,® and the SPORTdiscus databases; and the keywords
Results:
Yoga improved pulmonary function, as measured by maximum inspiratory pressure, maximum expiratory pressure, maximum voluntary ventilation, forced vital capacity, forced expiratory volume in 1 second, and peak expiratory flow rate, in all (N=9), but 1, study.
Conclusions:
Overall, pulmonary function appears to improve with a minimum of 10 weeks of regular yoga practice, and the magnitude of this improvement is related to fitness level and/or the length of time the subjects spend practicing pranayama (i.e., breathing exercises). In other words, greater improvements in pulmonary function are more likely to be seen in less-fit individuals and/or those that engage in longer periods of pranayama. Additional studies examining various yoga practices are warranted to gain a more comprehensive understanding of the effects of yoga techniques on pulmonary functions.
Introduction
Methods
The research articles for this review were identified by accessing the Alternative Health Watch, the Physical Education Index, Medline,® and the SPORTdiscus databases, as well as through reference lists of relevant journal articles. Each of these databases were searched using the key words
Using the aforementioned techniques, 57 studies were identified and considered for initial evaluation. These studies were separated into two categories: experimental and nonexperimental. Among these, only experimental studies involving clinical trials using yoga as the independent variable were included in this review. The clinical trials were subsequently broken down by health status (apparently healthy versus populations of patients with diseases) and only studies involving healthy individuals were selected for this review.
Results
The literature search identified 9 studies on pulmonary function in healthy subjects. Among these, 2 investigated the effects of regular yoga practice on respiratory muscular strength, 2,3 3 on ventilatory capacity, 4 –6 and 7 on overall pulmonary function. 3 –9 The specific yoga interventions are included in Table 1. Although only 1 study specified the style of yoga practiced, 7 all provided the exact duration of each specific yoga technique (e.g., pranayama, asana, dhyana, or dhauti), thereby allowing readers to make fairly educated assumptions about the style of yoga utilized in the intervention. Finally, all, but one yoga intervention, 10 produced positive changes in pulmonary function.
p<0.05; ** p<0.01; *** p<0.001; **** p<0.005.
— indicates no control; ↑, increase; ↓,decrease.
d, day; wk, week(s); min, minute(s); VC, vital capacity; S, significant; NS, not significant; hr, hour(s); FVC, forced vital capacity; FEV1, forced expiratory volume in 1 second; PEFR, peak expiratory flow rate; MVV, maximum voluntary ventilation; MEP, maximum expiratory pressure; MIP, maximum inspiratory pressure; PA, physical activity.
Discussion
Regular yoga training has been shown consistently to improve respiratory muscular strength and overall pulmonary function. 2 –9 Herein, this article reports the effects of yoga on: (1) respiratory muscular strength, as measured by maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) 11 ; (2) ventilatory capacity, as measured by maximum voluntary ventilation (MVV) 12 ; and (3) overall pulmonary function, as measured by forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), peak expiratory flow rate (PEFR), and vital capacity (VC). 12 Table 1 summarizes the results from studies investigating the effects of regular yoga training on these measures of pulmonary function in healthy individuals.
Respiratory muscular strength
Research conducted with various populations (e.g., 8th grade students to male medical students) revealed improvements in respiratory muscular strength following 3–6 months of regular yoga training. 2,3 For example, Madanmohan et al. 2 observed an average increase of 37% and 26% in MEP and MIP, respectively, in 27 male medical students who performed 30 minutes of yoga, 6 days per week, for 12 weeks. Although the results of this study should be interpreted with caution because no comparison group was utilized, in a later study, Madanmohan et al. 3 obtained positive results even when a control group was used. In that study, greater amounts of training over a longer period of time resulted in even greater improvements. Specifically, 45 minutes of yoga, practiced 6 days per week, for 6 months improved MEP and MIP by 57% and 117%, respectively, in 40 8th grade male and female students. In contrast, the sedentary control group did not have any improvement in either of these parameters. The positive results observed in both studies may be attributed, in part, to the breathing techniques (e.g., nouli, a rolling manipulation of the rectus abdominus, and mukh bhastrika, a bellows-type of breathing) practiced during the yoga sessions. As seen in Table 2, the medical students practiced nouli, 2 which has been purported to produce better neuromuscular control and enhance rectus abdominal and transverse abdominal strength and stability. 2,14 Similarly, the 8th grade students practiced mukh bhastrika, 3 which has been purported to strengthen the inspiratory and expiratory muscles through forceful and rapid breathing. 13
sec, seconds.
The dramatic improvements observed in the latter study may have resulted from the increased length of the intervention (6 versus 3 months) and/or the increased duration of practice (45 versus 30 minutes). Nevertheless, the results of the latter study are not generalizable to most adolescent males and females, as the researchers reported that the Indian subjects tended to have lower body mass indices, compared to their European counterparts. Thus, to advance the understanding of the effects of yoga training on respiratory muscular strength in adolescents, more research using adolescents with body weights and dietary habits typically seen in Western countries is warranted. From the limited data, it can be surmised, however, that yoga practice is likely to increase respiratory muscular strength in healthy populations of varying ages, and the degree of improvement appears to be related to the length of the intervention, as a longer intervention will be likely to produce greater improvements.
Ventilatory capacity
Research findings have also demonstrated that yoga improves MVV, an index of ventilatory capacity. 4 –6 Makwana et al. 6 observed positive training effects on MVV in 25 experienced male yoga participants who practiced yoga for 90 minutes per day for 10 weeks. Significant improvements in MVV were observed in the treatment group, but not in the study's sedentary control group (32% versus 2%). Surprisingly, in a study devoting more time each day to yoga practice and involving a longer intervention, less-substantial improvements in MVV were reported. 4 In that study, 30 male army soldiers, ages 25–35, performed 60 minutes of asanas and pranayama every morning as well as 60 minutes of asanas, pranayama, and dhyana every evening for 3 months. Results were compared to a control group that engaged in heavy physical activity for 3 hours per day. Although the average MVV for the control group remained unchanged, the average MVV for the treatment group increased by 10%. These results are quite surprising for two reasons: (1) The control group engaged each day in intense physical activity for a longer period of time than the treatment group and did not have any improvement in MVV, and (2) the treatment group had only modest changes in MVV. Although yoga training resulted in improvements in MVV in both studies, the former study reported much greater improvements in MVV than the latter study did, although the former involved less time for yoga practice each day (90 versus 120 minutes accumulated per day) as well as a slightly shorter intervention (10 weeks versus 3 months). Although the cause of this wide difference requires further investigation, it appears, based on the very limited findings, that regular yoga training will increase ventilatory capacity and that the magnitude of this increase may be affected by the fitness level of the person who practices yoga.
Overall pulmonary function
Yoga has also been shown consistently to improve results of overall pulmonary function tests in males and females of varying ages. 3 –9 In addition to the improvements in MVV, Harinath et al. 4 also observed increases in FVC, FEV1, and PEFR by 33%, 18.75%, and 6%, respectively, in a yoga group, but no changes in any of these measures in a physically active control group. These results supported the findings of an earlier study that used the same length of time (i.e., 3 months) and subjects with similar characteristics, (i.e., physically fit and active males). 8 In that study, 40 males, who had a history of being physically active, practiced 90 minutes of asanas, 60 minutes of pranayama, 15 minutes of dhyana, and 60 minutes of devotion per day, as well as attending two 60-minute yoga lectures per day. Twice each week, these participants also practiced kriyas (i.e., cleansing practices). Three months of intensive yoga training increased FEV1 by 18% and PEFR by 60%. Not surprisingly, the latter study reported much greater increases in PEFR than the former study did. These differences were probably the result of the greater number of minutes devoted each day to yoga practice (225 versus 90 minutes) in general, or to pranayama (60 versus 30 minutes) specifically, in the latter study compared to the former study. Nevertheless, the results of both studies should be interpreted with caution, as they both used fit men and required the subjects to practice yoga for at least 90 minutes each day of the week, a duration that may not be feasible for most Westerners.
It appears that shorter training sessions and intervention periods may also be effective for producing positive results on pulmonary function tests. For instance, Yadav and Das 9 investigated the effects of yoga using a shorter, more-realistic training duration. Sixty women practiced yoga 5 days per week for 12 weeks. Each 1-hour session consisted of 15 minutes of pranayama and 45 minutes of prayer, asanas, and meditation. After 6 weeks of yoga training, FVC and FEV1 improved by 13%, while PEFR did not change. After 12 weeks of yoga training, however, improvements in all three pulmonary function tests were seen. Specifically, FVC and FEV1 each increased by 26%, and PEFR increased by 10%.
The effects of yoga training on overall pulmonary function in other populations, including adolescents, 3 college-age individuals, 10 and smokers, 7 have also been investigated, albeit to a limited extent. Mandamohan et al. 3 observed that FEV, FEV1, and PEFR improved by 20%, 15%, and 24%, respectively, in adolescents practicing yoga for 6 months and remained unchanged in a sedentary control group. Furthermore, Birkel and Edgren 7 reported positive effects of yoga on VC in 287 college students of varying health status. After engaging in a variety of yoga styles and participating in pranayama for 50 minutes per session, two times per week, for 15 weeks, VC improved by 9% in students who smoked and by 10% in students who did not smoke. Although the nonsmoking students had the greatest gains in VC, it is important to note that regular yoga training enhanced the VC of both groups investigated. Unlike previous studies, this study included subjects of varying fitness and activity levels (i.e., athletes as well as active and sedentary nonathletes) and, thus, the improvements in VC have resulted, at least in part, from physical activity that the subjects may have engaged in outside of the yoga class. Despite this threat to external validity, this particular study used a sample, ranging in physical activity levels, health status, and ages (18–45), that is fairly representative of a normal sample population and provided the subjects with a reasonable amount of training in terms of minutes of yoga practiced per session over a fairly typical investigation period.
To the best of the current authors' knowledge, only 1 study reported no improvements in pulmonary function. 10 Ten healthy, untrained college-age students volunteered to participate in 90 minutes of yoga 4 days per week. Each session consisted of 10 minutes of pranayama, 15 minutes of warmup poses, 50 minutes of asanas, and 10 minutes of savasana (relaxation in corpse pose). Interestingly, FVC and FEV1 did not change as a result of the 8-week Hatha yoga practice. One explanation for the lack of improvement in pulmonary function may that there was a small number of participants (N=10). Nevertheless, based on the other 7 studies discussed in this review, regular yoga training appears to improve overall pulmonary function of adolescents and young-to–middle-age adults.
The positive performances on pulmonary function tests, such as FVC and VC, may have been caused by a number of physiologic adaptations. First, specific yoga asanas may help increase the flexibility of the shoulders, rib cage, and back. 7 Furthermore, by focusing on one's breath during pranayama, one consciously overrides the stimulus to the respiratory centers, leading to more conscious control over respiration. 2 During focused breathing, the lungs are emptied and filled more completely, which has been suggested to cause an increase in FVC and VC. 9 Specifically, the more often the lungs are completely filled and emptied, the greater improvement in FVC and VC can be expected. This logic may help explain why the studies that used longer and more intense training sessions, especially the studies that devoted more time to pranayama, produced greater improvements in FVC. Finally, yogic cleansing practices help cleanse the nasal and sinus passages, which may also improve pulmonary function. 9 These physiologic adaptations may help explain how yoga improves measures of pulmonary function significantly in healthy individuals as well as in some special populations.
Conclusions
Western versions of yoga, most notably Hatha yoga, have evolved from ancient Hindu teachings and focus on the physical aspects of yoga rather than the spiritual aspects. As illustrated in Table 1, all but one of the studies investigating the effects of yoga training on pulmonary function yielded positive findings despite using different methodologies and testing different populations. The duration of training (i.e., 10 weeks to 6 months), the amount of training in terms of time (i.e., 30 minutes to >2 hours per day) and frequency (i.e., 2–7 days per week), the style of yoga practiced with respect to breathing exercises and yoga postures, and the study population tested (trained versus sedentary, children versus adults, and nonsmokers versus smokers) resulted in varying degrees of improvement. Therefore, it is difficult to identify the specific training amounts and durations as well as the styles of yoga required to produce maximal pulmonary training adaptations. Based on the limited literature, it appears that yoga training will improve various aspects of pulmonary function. The magnitude of this improvement results, in part, from the total amounts of training in terms of minutes per session, days practiced per week, and overall duration of the training program. At a minimum, 10 weeks of yoga training, performed at least 2 days per week, for 1 hour is likely to produce some improvements in pulmonary function. Furthermore, it appears that longer individual sessions, greater frequency of training sessions per week, and/or longer intervention duration produce even greater results.
This review, however, identified several conflicting results, especially when examining the different styles of yoga practiced. Two studies used a Westernized version of yoga practice, 7,10 whereas other studies examined a more traditional or classical version of yoga. 2 –6,8,9 Classical yoga teaches that the asanas are the least important part and that pranayama and lifestyle changes (e.g., stress management, cleansing practices, and meditation) provide the most benefit. 15 Overall, it appears that Hatha yoga can provide pulmonary benefits to healthy populations, and it should be included as part of a regular fitness program. Research is lacking, however, on the effects of different styles of yoga on pulmonary function. Future studies should examine the effects of specific pranayama practices and asanas that are used to improve pulmonary function and capacity.
Footnotes
Disclosure Statement
No competing financial interests exist.