A within-subject comparison of different relaxation therapies in eliciting physiological and psychological changes in young women

Introduction

The body responds to stressors, whether physiological or psychological, by mounting a “fight or flight” response characterized by increased sympathetic nervous system activation. This results in increased blood pressure (BP), heart rate (HR) and glucocorticoid production (Brotman, Golden & Wittstein, 2007). The stress response is assumed to have evolved to ensure the survival of the organism, and as the two sexes may face different sources of stress, the nature of the response may itself differ between males and females (Kajantie & Phillips, 2006). However, chronic stress or an exaggerated response can be harmful (McEwen, 2008), and again could differ by gender.

Moreover, stress in women of reproductive age may have consequences not only for the individual, but potentially for her offspring. Maternal stress during pregnancy is associated with preterm delivery, low birth weight, and even adverse infant cognitive development (Beydoun & Saftlas, 2008; Bhang et al., 2016; Rondó et al., 2003; Talge, Neal & Glover, 2007). Similarly, during lactation, symptoms of maternal distress correlate negatively with breastfeeding success (Lau, 2001), and potentially with infant growth and behaviour (Mohd Shukri et al., 2019). Interventions to reduce maternal stress thus have the potential to improve mother and infant outcomes, and to lower the risk of pregnancy and breastfeeding complications. However, the use of psychotherapy in this population is challenging due to stigma and financial and logistical barriers (Goodman, 2009). This suggests a need for alternative simple therapies.

Relaxation techniques such as music listening (Knight & Rickard, 2001), relaxation training (Bastani et al., 2005) and mindfulness (Vieten & Astin, 2008) are reported to reduce stress and increase relaxation. Some studies have also described a reduction in stress hormones, such as cortisol (Chellew et al., 2015; Dolbier & Rush, 2012), and in symptoms of anxiety and depression (Manzoni et al., 2008). Light therapy might also reduce stress by stimulating the suprachiasmatic nucleus in the hypothalamus and modulating the release of cortisol and adrenocorticotrophic hormone (Pail et al., 2011). Studies have shown a reduction in HR, BP, oxygen consumption and carbon dioxide production following exposure to blue light (Cajochen et al., 2005; Litscher et al., 2013). Bright Light Therapy, which utilises blue light of high intensity (∼7000–10000 lux), has been consistently found in several RCTs to influence mood disorders such as seasonal affective disorder (Lam et al., 2006; Strong et al., 2009) and non-seasonal depression (Lam et al., 2016; Wirz-Justice et al., 2011). Colourful ambient lighting has also been used in medical settings and was shown to improve patient satisfaction and lower pain ratings (Robinson & Green, 2015).

Different stress markers have been used to measure the stress response. Psychometric tools, such as the Visual Analogue Scale (VAS) for Stress or Perceived Stress Scale, were developed and widely used by the medical community to assess cognitive changes due to stress. However, these tools are subjective, and it is not known whether they correlate with physiological markers of stress, especially acute stress. Moreover, VAS has shown good within-subject reliability and validity, but not between participants (Stubbs et al., 2000). Objective markers that assess the hormonal response to stress are also used; cortisol being the most commonly measured. The disadvantages of using these markers include the relative invasiveness, cost of analysis and difficulty of performing measurements in daily life. Other objective markers of stress include physiological measurements such as heart rate, blood pressure, skin conductance, skin temperature and respiratory rate. Currently, there is no general consensus on the optimal way to measure stress. Therefore, in this study, we selected the most feasible, non-invasive physiological and psychological markers which could be used in daily life to assess stress/relaxation.

It is unknown whether relaxation techniques differ in their ability to reduce stress measured by physiological and psychological parameters. Moreover, most studies test the effectiveness of relaxation techniques in populations diagnosed with mood disorders, and it is unclear whether similar physiological changes are observed in healthy or at risk individuals. Lastly, the relation between perceived relaxation/stress and physical relaxation measured objectively is unclear.

In this study we compared the effects of five simple relaxation interventions on physiological markers and perception of stress in women of reproductive age. Our aim was to establish the most effective technique(s) for use in this population, but also to identify the most promising interventions that are feasible for use in a future study investigating stress reduction in women who deliver prematurely.

Materials & Methods

Study design

This was a within-subject study, where each participant received five different relaxation techniques and one silence/sitting control state in random order over a 3-6 week period, to minimize carry over effects (Fig. 1). The primary outcomes –perceived relaxation (PR), HR, BP and fingertip temperature (FT) - were measured at baseline prior to each intervention and post-intervention. The participants were reimbursed at the end of the study for their time. The protocol and procedures were reviewed and ethically approved by the UCL Research Ethics Committee (ref 12521/001) and the trial was registered at Clinicaltrials.gov (NCT03592147).

Participants were recruited by advertisement using flyers displayed at University College London, UK. Interested women contacted the researchers and received information about the study. After checking eligibility and obtaining written informed consent, the participants were enrolled in the study and assigned a random order of interventions generated using a computerised random number generator.

Each participant was allocated one or two time slots per week (based on their preference and availability) to undergo the five relaxation interventions (guided-imagery meditation (GIM) audio, music listening (ML), “relaxation” lighting (RL), combination of RL and GIM, and a combination of RL and ML) and control sessions. All sessions took place in a private, quiet room with controlled lighting and room temperature. To reduce variability due to circadian rhythm effects on hormones and mood, all sessions were scheduled between 9AM and 1PM, whenever possible. The participants were asked to leave their belongings including any electronic devices or books outside the room

Baseline information was collected, including date of birth, ethnicity, occupation, history of treatment of psychiatric illness, and if currently pregnant or breastfeeding. The Perceived Stress Scale (PSS), a 10-item instrument that measures the extent to which one’s life is perceived as stressful or uncontrollable and overwhelming over the last month (Cohen, Kamarck & Mermelstein, 1983), was used to assess stress levels at baseline and at the end of the study.

Results

Preferences

Forty-three percent of the participants selected GIM + RL as their most preferred intervention, followed by GIM (24.1%) then ML (14.3%) and ML + RL (14.3%).

Perceived stress

At the end of the study, average PSS score (15.9 ± 5.6) was not significantly different from PSS at baseline (15.8 ± 5.2 ).

Perceived vs physiological relaxation/stress

No association was found between change (from pre to post intervention) in PR and change in SBP, DBP, HR, and FT. However, in the cases where change in FT was greater than 1.5 °C, increases in PR (measured using VAS) and FT were significantly correlated (r = 0.364, p<0.05 and when >2 °C, r = 0.470, p < 0.01).

Higher perceived stress, measured by PSS at baseline, was associated with a lower reduction in SBP following music (r = 0.615, p = 0.009) and GIM + RL (r = 0.495, p = 0.043). Change in SBP in participants with low vs high PSS was −7.9 ± 4.1 mmHg and −2.5 ± 4.7 mmHg following music and −4.2 ± 3.1 and −0.8 ± 5.9 following GIM + RL. This indicates that subjects experiencing lower stress levels in the previous month had greater reductions in SBP following relaxation interventions. Similarly, a lower reduction in SBP following music (r = 0.556, p = 0.02) and a lower increase in FT following silence/control (r =  − 0.643, p = 0.005) was associated with higher perceived stress at the end of the 3-6 week study. Participants with low vs high PSS at the end of the study had a mean change in SBP equivalent to −6.8 ± 5.8 mmHg and −2.2 ± 3.6 mmHg following ML, and a mean change in FT equal to 3.4 ± 2.8 °C and −0.2 ± 1.7 °C following control/silence.

Table 3:

Mean differences in primary outcomes following each intervention compared to the control State.

	Perceived relaxation (cm)		Systolic blood pressure (mmHg)		Diastolic blood pressure (mmHg)		Heart rate (bpm)		Fingertip temperature (°C)
Intervention	Mean (SD)	Effect size (d)	Mean (SD)	Effect size (d)	Mean (SD)	Effect size (d)	Mean (SD)	Effect size (d)	Mean (SD)	Effect size (d)
GIM
Control	1.49 (1.09)	1.4**	−1.78 (9.03)	−0.2	−0.52 (8.19)	−0.06	−3.15 (4.57)	−0.7*	0.50 (2.84)	0.2
Music
Control	1.26 (1.23)	1.0 **	−3.26 (6.31)	−0.5*	0.66 (6.94)	0.1	−2.00 (6.23)	−0.3	2.19 (3.06)	0.7**
RL
Control	0.03 (1.27)	0.02	−2.29 (6.00)	−0.4	−1.29 (8.25)	−0.2	−1.25 (5.82)	−0.2	1.01 (3.90)	0.3
GIM + RL
Control	1.09 (1.53)	0.7 **	−0.92 (5.31)	−0.2	0.64 (9.71)	0.1	−2.36 (5.88)	−0.4	1.18 (3.05)	0.4
Music + RL
Control	1.02 (1.85)	0.6*	−0.57 (8.13)	−0.1	2.24 (8.12)	0.3	−2.32 (6.42)	−0.4	1.10 (4.22)	0.3

DOI: 10.7717/peerj.9217/table-3

Notes:

*p < 0.05.

**p < 0.01.

Discussion

Previous studies have investigated light therapies, music listening, or meditation individually in relation to subjective assessment of anxiety, stress or depression. Only a few studied the effects of relaxation techniques on measurable physiological changes such as HR, BP, and FT. Moreover, many previous studies have focused on the short-term effects of stress interventions in special populations. Our study differs from previous studies as it assesses the short-term effects of different relaxation interventions in healthy participants.

All interventions and control significantly increased PR. Moreover, all interventions, but not the control, significantly increased FT while music significantly reduced SBP. When compared to control, however, GIM was the most effective intervention for increasing subjective feeling of relaxation and reducing HR. ML also significantly increased PR and FT, and decreased SBP compared to control.

The results are consistent with previous studies that showed any relaxation technique is capable of producing significant relaxation responses (Regehr, Glancy & Pitts, 2013). However, the advantage of the current study is the within-subject design that includes a control setting, which limits subject and environment variations. Comparing each intervention to the control demonstrated that GIM was the most effective overall when considering the physiological and psychological relaxation effects and preferences. ML produced a significant increase in FT, an indication of sympathetic nervous system stimulation, and a significant decrease in SBP. It is important to note that, on average, participants had lower baseline temperatures prior to the ML intervention. Having lower FT at baseline was associated with greater increases, whereas participants with higher FT at baseline had less potential for significant change. Thus, we controlled for the differences in baseline measurements by calculating the unstudentized residuals; however, the results remained unchanged indicating that music had an effect on FT and SBP regardless of the baseline value.

A similar within-subject study comparing the five interventions was recently conducted in Beijing, China, in mothers who were breastfeeding their healthy term infant (Yu et al., 2018). GIM was identified as the most effective relaxation intervention as it significantly reduced HR and increased PR compared to control, as seen in our study. Moreover, all treatments significantly increased PR. However, GIM also significantly decreased BP, and all treatments produced significant increases in FT and some reductions in BP, which was not observed in our study. The discrepancy in results might be due to the difference in characteristics of the two populations. Breastfeeding is associated with increased parasympathetic nervous system modulation and an attenuated stress response. Lactating mothers may also experience lower perceived stress levels, which might improve the response to relaxation interventions. The differences might also reflect cultural factors. The use of complementary and alternative medicine is more common in China than in the UK (Dixon, 2008), and is especially prevalent among lactating mothers (Sim et al., 2013). Breastfeeding participants in China might have been more receptive to the relaxation treatments than our sample of young women living in the UK, which might have enhanced their response to the interventions.

Interestingly, we found no association between the change in PR measured using VAS and the change in physiological measures (HR, BP, and FT). The discrepancy might be explained by the fact that subjective measurements such as the PSS and VAS are susceptible to recall bias, attention bias, and self-deception (Goyal et al., 2016). Conversely, objective measures rule out the possibility of these, but can be prone to measurement error and confounding effects of variables such as physical activity. The lack of association might be also due to the chemical basis by which the relaxation interventions were able to produce changes in physiological measurements. For example, oxytocin is known to produce anti-stress effects, which is evident in pregnant and lactating women who experience an attenuated stress response due to the increased levels of oxytocin (Moberg & Prime, 2013). Oxytocin has also been recognised as a cardiovascular hormone that can reduce BP and slow HR (Gutkowska, Jankowski & Antunes-Rodrigues, 2014). A recent study looking at the effect of relaxing (slow-tempo) and exciting (fast-tempo) music on salivary oxytocin and cortisol demonstrated that listening to relaxing music resulted in a significant increase in oxytocin (Ooishi et al., 2017). They also investigated the association between change in oxytocin and change in both HR and self-reported emotions (arousal). The ratio of increase in oxytocin was significantly related to the ratio of decrease in HR; however, oxytocin was not related to self-reported emotions. These results are consistent with our study, where the relaxation interventions elicited a physiological response which was not correlated with psychological/perceived relaxation. Further research is required to investigate the association between perceived, physiological, and biochemical mediators of relaxation.

By contrast, higher perceived stress measured by PSS was associated with lower changes in SBP and FT following certain interventions. Similar to our study, others have shown that the perception of stress is closely related to physiological measurements and might blunt cardiac reactivity to stressors (Gartland et al., 2014; Ginty & Conklin, 2011). Therefore, our results might indicate that, even though the participants experienced an increase in their PR measured by VAS following the different relaxation interventions, higher general perceived stress (measured using the PSS) might attenuate the more immediate physiological response to the interventions.

The majority of participants selected GIM + RL as their most preferred intervention, with the second most preferred options being GIM then ML. Physiologically, however, adding RL to GIM did not produce any additive effect, and it reduced the effect of GIM on HR and PR. GIM requires participants to follow verbal instructions, including concentrating on breathing and keeping eyes closed at certain time points. Conversely with the RL, participants might be inclined to focus on keeping their eyes open to benefit from the light. This might create sensory overload and counteract the relaxation response.

The strengths of the present study include the within-subject study design that also includes a control state. The main limitation of the study is the short duration of each intervention (6–7 min). Relaxation techniques such as lighting might require longer and repeated exposure to produce a relaxation response. However, we demonstrated that even with this short time period, some relaxation interventions could induce a response; we predict that prolonged and consistent use of those techniques might have further benefits. Further studies including a larger sample should investigate this. Another limitation was that we did not collect information on the phase of menstrual cycle or hormonal contraceptive use, thus we could not assess its influence on the reactivity to relaxation interventions. Lastly, we did not adjust the p-value for multiple testing which should be considered when interpreting the results.

Conclusions

In young women of reproductive age we were able to experimentally demonstrate that preference-based ML and GIM were the most effective interventions for reducing stress when compared to the control setting. These findings are informative in defining the most appropriate relaxation interventions for use in future studies aimed at stress reduction in women during pregnancy and lactation; by diverting the use of energy from stress and increasing energy investment in the infant, such interventions have the potential to improve pregnancy and breastfeeding outcomes. We found no association between perceived and physiological indicators of relaxation (HR, BP, and FT). Future studies should investigate this further, including biochemical indices of stress/relaxation, such as cortisol and oxytocin. Establishing associations between different indicators of stress/relaxation and clinical outcomes is also important in order to define the most appropriate outcome measures for use in studies testing relaxation interventions.

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