Differences in maximal inspiratory pressure when using a standard yoga mat versus a standard yoga block in healthy individuals

Introduction

Poor posture has become increasingly prevalent in all demographics, particularly in the sedentary population (Owen 2012). Although extensive research recommends frequent physical activity, people with chronic obstructive pulmonary disease (COPD) remain one of the most inactive populations and spend a significant amount of their time sitting or lying down (Furlanetto et al. 2017). Physiological changes related to COPD, including hyperinflation and thoracic kyphosis, compromise posture causing shoulder protraction, head protrusion and slouching (Goncalves et al. 2017). The slouching posture frequently observed in the COPD population compromises diaphragmatic function (Morrow et al. 2016; Albarrati et al. 2018). Habitual maintenance of this posture is also detrimental to spinal health (Castanharo et al. 2014) and is heavily associated with poor outcomes (Furlanetto et al. 2017). It is therefore important that people with COPD optimise their posture as far as possible.

Physiotherapy guidelines encourage the provision of patient education on appropriate postures as a self-management tool to combat the symptoms of dyspnoea and to reduce exertion (Bott et al. 2009). Certain postures can modify the ability of muscles to contract more forcibly in relation to the length tension theory (Kirsch & Stein 2000) thus improving their ability to utilise inspiratory muscles and inhale optimally. Good posture and specialised breathing techniques present in yoga practice have been associated with improved respiratory function and health outcomes, especially amongst people with COPD (Donesky-Cuenco et al. 2009; Fulambarker et al. 2012). Yoga can therefore be recommended as an adjunct to other therapies, particularly if the patient’s breathlessness interferes with moderate exercise.

Seating aids such as yoga mats and blocks are commonly used to optimise posture and facilitate comfort during yoga practice. Significant changes to body alignment can be observed whilst using certain yoga apparatus (Sheeran et al. 2018). Even slight changes in pelvic tilt of only 10 degrees away from neutral impacts on respiratory function (Hwang & Kim 2018). It is therefore important to consider the impact of seating apparatus on body alignment when choosing the most beneficial seating position for people with COPD in relation to pulmonary function during yoga practice. One way of measuring inspiratory muscle strength and thus general pulmonary function is by calculating MIP.

This study aimed to explore whether there is a statistically significant difference (p <0.05) in MIP in healthy individuals when sitting upon a standard yoga mat compared to a standard yoga block. We hypothesised there to be no significant difference between these two groups.

Methodology

Ethical considerations

Ethical approval was gained from the Cardiff University School of Healthcare Sciences Ethics Committee in August 2018.

Participants

Students from Cardiff University were invited to volunteer following a personal presentation by M.D. during two physiotherapy lectures. Inclusion criteria were: adults aged 18–35 years with a healthy BMI (18.5–24.9) to avoid compromising lung function due to excess adipose tissue compressing lungs (Banerjee et al. 2014) or malnutrition reducing respiratory function (Liu et al. 2015). Participants also needed to be capable of sitting crossed-legged (for uniformity) on the floor for up to 20 minutes without discomfort. Participants were excluded if they possessed any significant spinal deformities, acute or chronic respiratory conditions, had a history of smoking or were pregnant, due to the likelihood that their lung function would be compromised (Barroso et al. 2018).

Participants were provided with an information sheet detailing the purpose and nature of the research at least 24 hours before study commencement. If volunteers were eligible and happy to continue, a consent form was signed.

Data collection

A standiometer and weighing scale were used to measure the height and weight of each participant so that their BMI could be calculated on arrival. Each participant was then asked to sit crossed-legged on a yoga mat and yoga block (Figure 1).

The order of seating positions was randomised to eliminate any bias due to practice effect. This was attained through having the participants select one of the two seating positions from an opaque container. Participants sat for two minutes in each position to regulate their breathing before their MIP was measured using a Micro Respiratory Pressure Meter. Data were collected by a single examiner to avoid potential problems arising from inter-rater measurements. As MIP is an effort-dependent measurement the researcher provided standardised verbal encouragement using a specified script.

Adhering to ATS and ERS (2002) standardised guidelines, 3 correctly performed manoeuvres lasting for over 1.5 seconds were attained. A two-minute break in between each measurement was also given in order to regain participant baseline breathing pattern and reduce associated fatigue. Once 3 acceptable measurements in each sitting position, exhibiting less than 20% variance of each other, were collected (ATS & ERS 2002), the highest figure for each participant’s sitting position underwent further analysis using SPSS version 25.

Following spontaneous feedback regarding perceived comfort level using the apparatus, comments were recorded thereafter to identify any relationships. However, as this was not a part of the original study design, the recording of comfort was limited to stating which apparatus was more comfortable. No attempt was made to attribute a value to the degree of comfort for each sitting position.

Results

It is particularly important to consider the demographics as lung function can be influenced by age, gender and participant size (Bellemare et al. 2003). Of the 18 participants successfully recruited (Figure 2), 55% (n = 10) were female. Weight was normally distributed, and BMI fell within normal parameters (Table 1).

Table 1: Mean, standard deviation (SD) and range of demographic data.

Normal distribution was assessed and met parametric assumptions. A paired t test was therefore appropriate and showed that MIP was statistically significantly higher on the yoga mat compared to the yoga block with a mean difference of 3.61cm H₂O (t = 2.703, p = 0.015) (Table 2). In addition, all participants reported that sitting on a yoga block compared to a yoga mat was considerably more comfortable. However, this was not quantified.

Table 2: Mean, standard deviation (SD) and range of MIP values in sitting on yoga mat and sitting on yoga block.

Gender subsets largely also followed the same trend of mat MIP values being greater than those produced on the block however, male values generally exceeded female values. T tests confirmed that the order of seating positions did not affect results. This further suggests data consistency overall and within subgroups. There were no significant correlations between MIP and age, height, weight or BMI (suggesting that any differences were coincidental).

Discussion

This study showed that MIP was significantly greater when measured during sitting on a yoga mat, compared with a yoga block. Sheeran et al. (2018) reported that yoga block seating aids induced significant changes to posture and reduced overall flexion in lumbar spine and pelvic region. This encourages more upright sitting with a slight lumbar lordosis and anterior pelvic tilt, which is considered the optimal seating position for respiratory function (Castanharo et al. 2014; Sheeran et al. 2018). It is therefore surprising that MIP was universally lower on the yoga block compared to the yoga mat which encourages a posterior pelvic tilt. Additionally, a positive correlation between comfort and inspiratory muscle strength has previously been identified (Naitoh et al. 2014) which also contradicts the incidental results of this study where anecdotally, participants were more comfortable on the yoga block.

Considering the above factors, it might be expected that the block would produce higher MIP values than the mat. However, this study contradicted this expectation. There is no obvious physiological explanation for the above findings, but this difference may be explained by factors which this study had not been designed to formally address. These may include pelvic tilt, spinal angles, comfort or any other unknown influences. It is also important to consider whether the difference between positions is of any clinical importance. The small difference in MIP (only 3.61cm H₂O) makes it unlikely to have a significant clinical impact on the participant.

Maximal inspiratory pressure is one of the most commonly used measures for respiratory muscle strength and is recommended by ATS & ERS (2002) as a diagnostic tool. Yet, MIP devices are less commonly used in clinical practice and are not currently considered suitable as protocol tools in respiratory function testing (Culver et al. 2017). Although MIP is not as reliable as other, invasive, non-volitional methods, data collected in this study shows a stable variation across the range of MIP values. This suggests that the machine performed as expected and that the examiner technique was consistent thus supporting the reliability of the results.

There is a wide range of normal MIP figures amongst the general population (Pessoa et al. 2014) and no distinct pattern has been identified by previous studies. However, no minimum clinically important difference (MCID) has been reported in the literature and it is difficult to estimate whether differences are significant. This study revealed no evident correlations in relation to MIP and age, height, weight or BMI in the sample used. It could therefore be assumed that MIP is not dependant on these variables. Hence these results may be considered applicable to the young, healthy population. However, there may still be a limited applicability of these results to the unwell population such as those with respiratory, musculoskeletal or neurological disorders for which this study was not intended.

Conclusion

This study revealed that sitting on a yoga mat yielded greater MIP values (104cm H₂O) than sitting on a standard 5cm yoga block (100.39cm H₂O). Due to the statistically significant difference (p = 0.015) the null hypothesis was rejected. However, as the range of normal MIP values in the studied population is so great (>90cm H₂O), without a reported MCID in existing literature, it is difficult to say whether the difference of 3.61cm H₂O between both seating positions has any significance in clinical practice. Furthermore, it is currently unknown whether this information would be transferrable to those with long term respiratory conditions such as COPD where a 3.61cm H₂O difference would represent a greater proportional change compared to those with healthy respiratory systems and higher MIP values.

The strengths of the study include having a single data collector to avoid inter-rater differences. However, the small size of the study and convenience sampling method of young and healthy participants is not representative of the general population.

Further research incorporating measurements of spinal angles, pelvic tilt and perceived comfort might contribute to a fuller understanding of these results. As the clinical applicability of this study is unknown, it would also be particularly helpful to repeat this study in people with COPD.

Key points

• Sitting position influences inspiratory muscle performance and therefore should be considered during yoga practice.

• In healthy individuals, sitting on a yoga mat produced higher results compared to sitting on a yoga block, despite being no apparent physiological explanation.

• The applicability of MIP measurements to the general population may be hindered by the apparent lack of recognised MCID values.

Funding and acknowledgements

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. I would like to acknowledge and thank the 18 participants who volunteered for this study.

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