Effects of Bikram Yoga Clothes on EEG Beta Spectrum

Clothes provide physical, physiological, and psychological comfort [1]. Functional clothing can define specific user requirements; it is designed or engineered to meet the performance requirements of the user under specific conditions. A variety of functional clothing products are available in the market as sports clothing, medical clothing, protective clothing, and so on [2]. Take, for instance, the clothes worn during Bikram yoga (a form of hot yoga), which is performed in a hot environment and is touted to provide the practitioner with good mental health as well as optimal physical performance, mobility, and physiological responses. Yoga incorporates physical exercise with deep relaxation, specific breathing, and meditation exercises [3]. It is known to enhance not only physical abilities but also emotional stability and concentration [4, 5]. In particular, Bikram yoga includes a breathing therapy called Kapalbhati, which increases mental activity and induces a calm alert state [6].

With the development of science and technology, electroencephalogram (EEG) testing has become widely adopted as a neurophysiological evaluation method for determining the degree of higher-order cognitive functions such as attention concentration. EEG is induced and amplified through electrodes attached to the skull, and the electric potential is recorded; this electrical signal is converted to the frequency axis and expressed. Studies that have measured mental and emotional states during yoga through EEG measurements reported that brain activity increases with breathing, meditation, and motion [7]. Furthermore, the alpha wave related to the respiratory system, mental relaxation, and tranquility increases after yoga [7, 8, 9]. There are also reports that the beta wave is closely related to concentration, alertness, stimulation, and caution when sitting upright after yoga or performing moderate physical activities [5]. Yoga assists their sense of acceptance and focus [10]. Another study found various cognitive benefits, inlcuding increased memory and attention-switching capacity in older adults in relation to cognitive benefits [11]. If there are articles of clothing that can add value to these fundamental yoga effects in terms of their influence on mental traits or activity, this will support yoga clothes’ true function. In short, yoga clothes should be developed using multidimensional analysis in order to optimise comprehensive functionality. As the purpose of performing yoga is mental and physical health, a new approach is needed to evaluate yoga clothes.

Exercising in a hot environment generates heat, leading to higher core and skin temperatures and, ultimately, perspiration. Therefore, functional clothing must be able to manage sweat while facilitating evaporation [12, 13]. Studies of comfort clothing for hot environments have mainly focused on methods for alleviating thermal stress based on fibers and materials [14, 15] or on evaluating performance enhancement and ease of movement [16, 17]. However, research on these properties in yoga clothing are limited, and there are even fewer studies of the psychological effects of yoga clothing. There are no studies that have evaluated EEG with yoga clothes set as a variable. However, such attempts are significant considering the psychological efficacy of yoga. As mentioned earlier, several studies have examined the generation of alpha waves in relation to relaxation and calm during yoga, but relatively few have examined beta waves in relation to concentration, arousal, and stimulation, and very few such studies have been related to clothing. By specifically analysing indicators related to beta waves in the context of yoga's various requirements as it is performed by modern people, we aimed to examine whether and how clothing can provide efficacy of attention.

The aim of this study was to (1) evaluate the psychological effects of clothing conditions (clothing pressure, Qmax, and absorption) when performing yoga in a hot environment through EEG measurements, (2) examine their relationship with subjective evaluations, and (3) investigate the conditions for yoga clothes that provide high-level functionality and comfort optimised for attention and mental focus. Comprehensively, the purpose of this study is to identify the design elements of yoga clothes that have a beneficial effect on mental concentration when performing yoga in a hot environment.

Though yoga itself is known to activate brain waves, this study showed that brain wave activity can either increase or decrease after yoga depending on the yoga clothes worn. Thus, yoga clothing can be considered a major variable and has a proven neurophysiological effect on yoga activity. The standardised design properties of yoga clothing, pressure and subjective preference (depicted in Figure 6), were used to analyse how the characteristics of the yoga clothes affected subjective sensations and brainwaves. Participants preferred G3 in a hot environment for its coolness and comfort. Radar charts of G3 occupied relatively large areas, as shown in Figure 6. The graph that stands out here is G2. G2 had a negative evaluation in subjective preference and a high response frequency regarding areas that were uncomfortable with sweat; it showed a low index in all items, including absorption in the standardised score. As the chamber had no air circulation and was set to a high temperature, it appears that the subjects were more sensitive to absorption than the initial contact coolness. The moisture transmission behaviour of clothing is a thermophysiologically critical factor [22, 23]. However, as perspiration does not easily evaporate under experimental conditions, absorption becomes more important than other functions.

Fig. 6

Yoga is associated with the perception of calmness, as it significantly increases alpha activity through physical exercise, breathing, and meditation, regardless of clothing worn, rendering the performer's temporality idle but still alert [7, 8, 24]. Furthermore, it is known that yoga activates brain waves, such as beta waves, which promote relaxation, alertness, and concentration [5, 25], as well as theta waves, which improve internal attention [26]. However, unlike previous studies, which examined a broad bandwidth, this one intricately divided the bandwidth to derive a precise analysis of how brain activity differs before and after performing yoga in dependence on the yoga clothes worn.

G1 generally enhances concentration and caution while reducing anxiety and alertness. G2 decreased anxiety and tension, but the difference was not significant. G3 decreased alertness, anxiety, tension, and concentration. G4 enhanced the concentration while reducing anxiety and tension. Only G2 significantly reduced the RMB wave, but displayed a low preference by participants during subjective evaluation; it was the only set with low Qmax, absorption, and pressure. Analysis of G1 and G2, which both had relatively low pressure, showed that G1 increased RMB more than G2, positively affecting the activation of the beta wave. Both were negatively addressed in the subjective evaluation, but G1 did not show negative results in the EEG measurements. Meanwhile, G3 and G4, which had relatively higher pressure, also lowered anxiety and excitement, implying that a certain level of clothing pressure is required for yoga. Specific clothing pressure can positively affect joint movement, blood circulation, mental support, and enhancement of concentration during exercise [27]. Erhui and Yanzhen [28] state that the pressure comfort of garments varies according to the type and intensity of body movement; thus, numerous factors must be considered when selecting the optimal pressure for functional clothes. When all factors that affect comfort are applied harmoniously, a virtuous cycle positively affects the wearer's emotions, senses, and performance. Lee et al. [27] examined how compression pants set to different levels of clothing pressure affected the EEG spectrum and found that a pressure level of 1.57 ± 0.41 kPa significantly enhanced attention and concentration, serving as an analytical basis for the phenomenon discussed above. In the repeated ANOVA measurement results for the pressure between experimental garments, the RMB increased for G1, G3, and G4 but did not significantly affect G2. G2 showed different trends in the subjective evaluation of subjects as well as in the results of EEG measurement. It was difficult to make the fabric comfortable for hot, sweaty bodies, and the pressure was the lowest as well; hence it could not provide the tension possible with tight fitting clothes. Exercising in a hot environment generates heat, leading to higher core and skin temperatures and, ultimately, perspiration. Therefore, functional clothing must be able to manage sweat while facilitating evaporation [12, 13]. These clothes should be able to reduce skin moisture through moisture transfer and improve sweat evaporation to improve thermoregulation [23]. There is an association between sweating events and brain regions involved in arousal [29]. Ftaiti et al. [30] reported that performing exhausting activity in the heat induced a change in brain activity and that beta activity was significantly decreased in hot and neutral environments because the fatigue brought on by heat affects brain activity. Since G2 was low for all indicators, it was functionally less effective at managing the physiological discomfort and fatigue caused by sweating than the experimental sets of clothing. Thus, G2 did not satisfy the physiological and physical conditions for the wearer. Generally, favorable functions of synthetic sportswear include faster heat transfer, better moisture vapour transmission, and a cooler feeling, all of which contribute to a comfortable wearing experience [31, 32].

In summary, results meaningfully changed depending on the clothing, signifying that yoga clothes affect brain waves during yoga activity and that optimal conditions do exist. The results confirm that clothing with absorption of perspiration was preferred both physiologically and subjectively. Clothing pressure also contributes to faster sweat absorption, as it increases the contact area between the clothing and the body. Since clothing environments significantly affect beta waves during yoga, it is very important to evaluate and design the high-level functionalities of yoga clothes while considering their mental and physical effects.

This study scientifically examined the effects of clothing in a special environment while performing yoga. Yoga clothing affects brain potential while practicing yoga, and even subjectively disliked yoga clothes (G2) caused negative brain wave responses. While details regarding brain waves varied, almost all yoga clothes enhanced concentration post yoga (except G2). The clothing combination that offered higher pressure and absorption, and enhanced concentration while lowering excitation and anxiety, proved to be most beneficial for the mind after yoga, as measured by EEG. This study has novelty in that it quantitatively measured materials and clothing design elements and scientifically analysed EEG, unlike studies that depend only on subjective responses for the mental state according to each wearing combination. Moreover, it can be seen that the functionality of the material does not directly lead to functionality of clothing, and all conditions must be comprehensively considered for clothing to properly execute its intended functions. These results will be meaningful information not only for clothing buyers but also for designers. Additionally, products developed should also consider brain neuroscientific evaluation as such evaluation results can be utilised as highly effective marketing aspects.

However, the experimental garment used in this study was a set of clothes that was available in the market, and this lack of choice limited the control conditions. Although there are limitations in evaluating products purchased from the market, it is meaningful that random variables were standardised and analysed by statistical methods. The small number of participants, even though they were professional practitioners, was another limitation of this study. Future studies should experiment with the general population.