Along with strength, balance, and endurance, flexibility is considered an important physical dimension for active and healthy aging. In this regard, Nelson and coworkers reported that “to maintain the flexibility necessary for regular physical activity and daily life, older adults should perform activities that maintain or increase flexibility on at least two days each week for at least 10 min each” [1
]. Yoga was shown to beneficially affect physical function and well-being in seniors and can thus be considered an appealing and easily applicable activity for this population [2
]. Sauna, on the other hand, delivers a warm and relaxing environment, where the body and mind can be trained simultaneously. From a risk–benefit stand point, and in the light of stress, sleep, and mental benefits, only very few adverse events were reported [3
]. Culturally, the sauna is very popular in Scandinavia, particularly in Finland, but it also strongly belongs to a worldwide spa culture. Many fitness and sports clubs provide saunas that are easily assessible.
Even though the potentially beneficial effects of both sauna and yoga are independently well studied and reported, there is hardly any literature concerning training on health-related surrogates of physical fitness, such as flexibility when employing a sauna with moderate temperatures. Training in a warm environment, however, was reported to improve the range of motion (ROM) [4
], accompanied with reductions in perceived pain [6
]. One acute study led by Leung and colleagues [7
] interestingly reported acute responses after Qigong training in a Sauna: Leung et al. [7
] observed higher heart rates of 30–40% above the pre-exercise level, whilst blood pressure, on the contrary, remained stable or even slightly decreased after a single Qigong session.
Thus, sauna yoga might serve as a comprehensive body–mind exercise approach which aims to improve spine and shoulder flexibility, accompanied with exercises that strengthen the muscles in the trunk and lower extremities by using slow-paced stretching and strengthening exercises in a quiet and mildly warm environment. One sauna yoga session lasts 30 min and is performed in a sauna room with a temperature of approximately 50 °C. To the best of our knowledge, however, no longitudinal intervention study investigating the effects of combining the sauna with yoga on health-related physical fitness parameters was published.
Against this background, the present two-armed randomized controlled trial investigated the effects of sauna yoga on flexibility as a primary outcome and strength, balance, and quality of life as secondary outcomes. We hypothesized that one weekly sauna yoga session over eight weeks would lead to superior improvements in flexibility compared to yoga performed in an ambient room temperature. As a secondary hypothesis, we assumed that strength, balance, and quality of life does not superiorly improve after sauna yoga.
The aim of this two-armed randomized controlled trial was to gain new insights into the potential effects of sauna yoga on relevant physical health outcomes (flexibility, strength, and balance) in healthy and relatively active older adults. To the best of our knowledge, no previous studies addressed this issue in a controlled study with parallel study arms, assessing both physical dimensions and quality of life. It was hypothesized that sauna yoga can beneficially affect spinal, shoulder, and hamstring flexibility, whereas only little effects on lower-extremity strength and static balance performance were expected. The results of this study indicated that, after only eight session over eight weeks, flexibility using the CSR test notably improved in favor of the INT group, whereas shoulder flexibility and lateral spinal flexibility were not relevantly affected. Interestingly, small but meaningful changes in favor of the INT group with slightly significant results were also found for lower-extremity strength and static balance with closed eyes. Thus, our previously postulated hypothesis was only partly confirmed.
In the light of previous research on yoga training, significant improvement in flexibility could have been expected. However, only few studies have been undertaken in the elderly population. In comparison to the study of Gonçalves, Vale, Barata, Varejão, and Dantas [26
], which showed a significantly improved range of motions (ROM) in the shoulder girdle and in the spine, our study applied a comparatively shorter intervention period, lower weekly training intensity, and a moderately warm environment of 50 °C.
The effects of chair yoga in ambient temperature without using a sauna environment was studied in the past, but mostly in relation to psychological dimensions, like fear of falling or quality of life. For example, Furtado et al. [27
] were not able to show any improvements in physical fitness outcomes after 14 weeks of chair yoga in a group of institutionalized older women. Furthermore, Park, McCaffrey, Dunn, and Goodman [28
] were more focused on the assessment of clinical symptoms perception of osteoarthritis.
Based on the findings of our study, performing yoga poses in a seated position in a warm environment can superiorly improve flexibility in healthy community-dwelling older adults. The current study is thus partly in line with earlier studies that revealed effects of yoga on strength and balance in the elderly [29
]. However, compared to many yoga studies, the weekly intensity of the present intervention was comparatively low. In other yoga studies, yoga classes were performed two to three times weekly [30
]. Additionally, the session duration was longer than in sauna yoga, and it was also longer than in the hot yoga interventions [33
]. However, the participants were younger (46 ± 12; 53 ± 2 years) than the ones in our intervention group (69 ± 5 years). Furthermore, it should be taken into consideration that the room temperature in sauna yoga is approximately 10 °C higher than in hot yoga and 30 °C higher than in normal yoga. With more frequent sauna yoga sessions, the improvements could have been more pronounced from a dose-response perspective. On the other hand, normal sauna visits are also performed once to twice weekly, for approximately 15 min [35
Results of a six-month yoga intervention study in the elderly indicated beneficial effects on physical health, psychological health, social relationships, and environmental domains of QoL [36
]. Gonçalves et al. [26
] showed significant changes in overall QoL and in the dimensions of physical health and environment. However, in the present study, significant effects were detected only in the environmental domain of QoL in favor of the INT group, and the effects were smaller than in the study of Hariprasad et al. [36
] or Gonçalves et al. [26
]. The participants of this study were moderately or highly active, which may affect detectability in QoL, as the QoL is associated with physical independency and mobility.
Dewhurst and Bampouras [37
] recommended that when measuring flexibility with CSR or BS, both sides should be measured separately, so that the side differences can be detected. In this study, the participants could choose themselves which side they wanted to have measured. However, the side was noted, and the same side was measured in the post measurements. CSR and BS are highly reliable when repeated and executed within a short period [37
]. As recommended, both tests were performed twice, without familiarization. In future studies, both sides should be included in the measurement, to produce more detailed information on the side differences and flexibility imbalance.
Standing balance testing is reported to be rather easily applicable for community-dwelling adults [21
] and a ceiling-effect in standing balance with closed eyes is not likely. In this regard, testing static balance with EC is noted to be very sensitive to the influence of age [38
], and the time limit of 10 s with EC is adopted in some geriatric studies [39
]. It was repeatedly emphasized that, in the future, more specific tests need to be chosen for assessing static balance, e.g., center of pressure path length at force plate. The current study did not measure the changes in trunk strength, even though it is associated with postural control [41
]. Additionally, many poses aimed to improve trunk strength. This test parameter should be considered in future studies concerning sauna yoga and strength.
Although the sample size of this study refers to a pilot character, we were able to detect significant and meaningful change in the primary endpoint. Thus, the sample size can be regarded as sufficient. Initially, we intended to examine the feasibility of using yoga in a warm sauna environment to affect physical health outcomes in a group of healthy, active seniors. When considering the present data, general neuromuscular transfer effects to flexibility, strength, and balance can be expected. The strongest improvements have been found in flexibility, as this part was the main focus of attraction throughout the training sessions. Against this background, the authors recommend further studies on sauna yoga in order to gain more information on training interventions that can improve overall long-term mobility, strength, and balance in healthy elderly subjects. The study also suggests that the effects of sauna yoga should be studied with a greater number of participants and a longer intervention period, with increased weekly intensity.
During the intervention, none of the participants complained about inconvenience or negative effects regarding sauna yoga. On the contrary, only positive feedback was given, and participants enjoyed and looked for further sessions. Therefore, it is recommended that sauna yoga under supervision is a suitable activity for healthy older adults and can be incorporated into an activity program in spas, fitness centers, and senior activity centers. Additionally, the results of current this research may lead to a new perspective on thermal therapy as treatment for diseases that decrease ROM (e.g., arthrosis and rheumatism).