Quran memorisation and heart rate variability: How do they correlate?

Abstract

BACKGROUND

Heart rate variability (HRV) was shown to be affected by performing religious activities.

AIM

To examine the relationship between the level of Quran (the holy book of Muslims) memorisation and HRV among teenagers.

METHODS

This experimental study included 16 Tahfiz students and 16 non-Tahfiz students (n = 32). The HRV was measured in three tasks: Recalling familiar verses, memorising new verses, and recalling the newly memorised verses of the Quran. HRV analysis was done using these parameters: Standard deviation of N-N (heartbeat peak) interval; low frequency (LF); high frequency (HF) and LF/HF ratio.

RESULTS

There were significant differences between tasks for all parameters (P < 0.05). However, between the groups, only the LF/HF ratio had significant differences, with F = 5.04, P < 0.05. Pearson correlation showed a moderate positive correlation between the number of pages memorised and the LF/HF ratio (r = 0.61, P < 0.05).

CONCLUSION

Quran memorisation increased the HRV and our results suggested that this activity could be developed as an effective sympathovagal modulation training activity.

Key Words: Heart rate variability; Autonomic nervous system; Quran memorisation; Tahfiz student; Heartbeat

Core Tip: The process of Quran memorisation increases the heart rate variability in several ways. The spiritual and meditation practices have been linked to heightened parasympathetic and reduced sympathetic cardiac regulation. It activates both sympathetic and parasympathetic actions with the increase of standard deviation of N-N (heartbeat peak) interval and low frequency values. Heart rate variability is believed to play an important role in diagnosing cardiovascular autonomy disorders in children and adolescents.

INTRODUCTION

Heart rate variability (HRV) is the temporal variation of consecutive heartbeats or the fluctuation that occurs within the R-R interval[1]. It reflects the heart’s adaptability to detect and quickly respond to unpredictable stimuli. This is due to the autonomic neural regulation, which involves sympathetic and parasympathetic nervous systems that control the autonomic nervous system in a dynamic balance. Hence, when the variability is higher, the sympathovagal balance is improved. The balancing is vital in regulating the contributing risk factors towards cardiovascular diseases.

HRV analysis is commonly done using the time domain and the frequency domain[2]. The time domain quantifies the amount of variability by measuring the interbeat interval that indicates the period between successive heartbeats. The calculation involves the R-R interval in consecutive heartbeats, such as mean inter-beat-interval, standard deviation, standard error of mean and a few other related parameters[2,3]. The frequency domain estimates the distribution of absolute or relative power into four frequency bands: Ultra-low-frequency, very-low-frequency, low-frequency (LF), and high-frequency (HF) bands[4]. The LF band is related to the combined sympathetic and parasympathetic action, the HF band is the parasympathetic indicator while the LF/HF ratio shows sympathetic effects[5].

There are many factors that affect HRV, such as physical activity, stress, obesity, age, gender, genetics, breathing rate, smoking and religious activities[6-10]. Many studies had proven that religious activities could positively affect the HRV[10,11]. For example, studies showed that recitation[12] and listening[13,14] to the Quran could improve HRV, but studies on the relationship of Quran memorisation and HRV has yet to be done. Since there are many factors that could also affect memorisation, such as stress, attention and emotion[15], understanding the mechanism of memorisation that affects the HRV is similarly relevant.

Memorisation of the Quran possesses many benefits. Studies have found a positive correlation between memorisation of the Quran and academic achievement[16]. Memorisation of the Quran could also improve human manners and behaviour[17]. Cognitive ability and memory were increased, and the intelligent quotient level was also higher in students who memorised the Quran[18,19]. Activation of the hippocampus and neocortex during the formation and retrieval of memories during the process of memorisation is linked to higher brain activation and function[20]. Thus, memorisation of the Quran is able to give a variety of positive effects on human physiological functions.

In Muslim communities, memorisation of the Quran is an important religious activity[21]. In Malaysia, specialised schools, known as Tahfiz schools, integrate Quran memorisation as part of the curriculum at the primary and secondary levels. Many parents have made Tahfiz schools as the preferred choice for their children to enrol in[22]. As this type of school becomes more popular and gets attention from the parents, it is important to investigate the health status of the Tahfiz students. HRV testing may play an important role in detecting cardiovascular autonomy disorders even in children and adolescents[23]. Therefore, our study was aimed to determine the effects of memorisation of the Quran on the HRV of the Tahfiz students.

MATERIALS AND METHODS

Participants

This experimental study involved 32 male students from two Tahfiz schools (n = 16) and two non-Tahfiz schools (n = 16) in the state of Selangor, Malaysia. Their age ranged from 13-17 years old. The schools were selected by purposive sampling, while the students were stratified based on four different Quran memorisation levels according to their sections classification. The Quran is divided into 30 parts of equal lengths or juz’. The levels are level 0 (less than one section (non-Tahfiz), level 1 (one to 10 section), level 2 (11-20 section), and level 3 (21 to 30 section). Within the stratum, the students who returned the consent form were recruited into the study. The students from both the Tahfiz and non-Tahfiz groups were matched by their age, gender and body mass index (BMI). The inclusion criteria for the study were students who stayed in hostels while the participants who had been diagnosed with any cardiovascular problems were excluded. This study was approved by the Institutional Human Ethics Board of Universiti Kebangsaan Malaysia (UKM PPI/111/8/JEP-2018-319).

HRV measurements

HRV reading was recorded by using CamNtech^® Actiheart Sensor and Actiheart Reader (England). The mobile device was operated by two-leads electrocardiography placed at the V1/V2 and V4/V5 areas of the chest, allowing HRV determination by the magnitude between each heartbeat. HRV parameters were divided into two main domains: Time and frequency domains. The time domain involved the standard deviation (SD) of the R-R (ms) while the LF, HF, and LF/HF ratio were grouped into the frequency domain (ms²).

Memorisation test

The HRV was measured using a test that consisted of a series of tasks involving Quran memorisation activities. The test was comprised of three different memorisation tasks as follows: (1) Task 1: Recalling familiar verses; (2) Task 2: Memorising new verses; and (3) Task 3: Recalling the newly memorised verses. HRV readings were measured throughout these tasks for 5 minutes, 10 minutes, and 5 minutes, respectively, with 3 minutes resting interval between the tasks. For Task 1, the participants were required to recall verses that they were familiar with. For Task 2, the students had to memorise verses that they were not familiar with. Finally, in Task 3, the students were required to recall the newly memorised verses in Task 2. The flowchart of the test is shown in Figure 1.

Figure 1  The flowchart of memorisation test.

Data analysis

The data was analysed using the IBM Statistical Package for Social Science (SPSS) version 23. Descriptive analysis was employed to illustrate the background of the participants. The means differences from all HRV parameters between the Tahfiz and non-Tahfiz group, and across different memorisation tasks were determined by a mixed-design ANOVA. Lastly, Pearson’s correlation was used to correlate between the memorisation levels and HRV.

RESULTS

Participants’ background

Table 1 shows the demographic data of the students involved. The mean age was 14.78 ± 0.19 while the mean BMI was 20.03 ± 0.53. All non-Tahfiz students memorised not more than one section, while the number of Tahfiz students who memorised 1-10 section was 4 students, juz’ 11-20 was 6 students and section 21-30 was 6 students.

Table 1 Demographic data.

Students	Tahfiz (n = 16)	Non-Tahfiz (n = 16)	Total (n = 32)
Age (years)	14.94 ± 0.37	14.63 ± 0.15	14.78 ± 0.19
BMI (kg/m2)	20.95 ± 0.77	19.7 ± 0.67	20.03 ± 0.53
Total Juz’ memorised
< 1 section	-	50%	n = 16
Section 1-10	12.5%	-	n = 4
Section 11-20	18.8%	-	n = 6
Section 21-30	18.8%	-	n = 6

BMI: Body mass index.

Time domain analysis

SD of N-N (SDNN) was measured for the time domain across three memorisation tasks for both Tahfiz and non-Tahfiz group using a mixed-design ANOVA (Figure 2). There was a significant difference between tasks [F(2,62) = 15.11, P < 0.001]. However, there was no significant difference between type of schools [F(1,31) = 0.20, P = 0.66] and no significant difference was observed for the interaction effects (type of schools vs tasks) [F(2,62) = 1.56, P = 0.22].

Figure 2 Simple scatter plot with fit line of number of pages memorised vs heart rate variability domains for Tahfiz group. A: Low frequency (LF); B: High frequency (HF); C: LF/HF ratio; D: Standard deviation of N-N. LF: Low frequency; HF: High frequency; SDNN: Standard deviation of N-N.

Frequency domain analysis

The parameters involved for the frequency domain were LF, HF, and LF/HF ratio. The results are represented in Figure 3. For LF domain, there was a significant difference between tasks [F(2,62) = 14.754, P < 0.001]. There was no significant difference between type of schools [F(1,31) = 0.078, P = 0.781]. However, no significant difference was observed for the interaction effects (type of schools vs tasks) [F(2,62) = 2.061, P = 0.136] (Figure 3A). The main effect of tasks on HF domain was significantly different [F(2,62) = 4.385, P < 0.05]. The main effect, type of schools on HF domain was not significantly different [F(1,31) = 0.624, P = 0.436]. According to Figure 3B, there was a significant difference observed for the interaction effects (type of schools vs tasks) [F(2,62) = 4.342, P < 0.05]. The mean values of HF for Tahfiz group were consistent throughout the different tasks. In contrast to the non-Tahfiz group, the HF value was peaked in Task 3. For LF/HF ratio domain, there was a significant difference between tasks [F(2,62) = 12.226, P < 0.001]. There was a significant difference between type of schools [F(1,31) = 5.229, P < 0.05]. It was observed Tahfiz school showed higher mean values. However, no significant difference was observed for the interaction effects between type of schools vs tasks [F(2,62) = 0.021, P = 0.98] (Figure 3C).

Figure 3 Simple scatter plot with fit line of number of pages memorised vs heart rate variability domains for non-Tahfiz group. A: Low frequency (LF); B: High frequency (HF); C: LF/HF ratio; D: Standard deviation of N-N. LF: Low frequency; HF: High frequency; SDNN: Standard deviation of N-N.

DISCUSSION

In this study, we focused on the effects of Quran memorisation on the HRV in Tahfiz and non-Tahfiz students. Our results showed positive significant effects for both the Tahfiz and the non-Tahfiz students, suggesting that the process of Quran memorisation can affect adolescents within these age ranges. Religious practicing may involve praying to God for strength and comfort, wisdom, health, healing and help for loved ones. This practice may involve reading Holy Scriptures such as Torah, Bible or al-Quran[24]. According to Weaver and Koenig (2006)[25], religious or spirituality may be associated with positive health outcomes particularly cardiovascular health.

The SDNN value showed a significant difference between Task 1 and Task 3 even though both tasks involved recalling memorised verses for both groups. Recalling the newly memorised verses increased SDNN while recalling familiar verses reduced SDNN, suggesting that the students were most probably in a relaxed state while performing Task 1. Another study also found similar findings when subjects were listening to Quran recitations[14].

Analysis of the frequency domain revealed that all parameters showed significant differences across the three tasks. The highest LF mean was noted at Task 2, as the process of memorisation involved both sympathetic and parasympathetic activation. This was probably due to the stress that was stimulated when the students had to complete a task within a set time frame, which resulted in an increased sympathetic action. Furthermore, both focus and selective attention, which were given while performing memorising activities also yielded a similar effect of increased sympathetic action[15]. Interestingly, this selective attention, which is often engaged in memorisation activities, is also proportionally increased with parasympathetic activity[26]. Spiritual or meditation practices have been reported to be associated with increased parasympathetic and decreased sympathetic cardiac control[27]. Recitation of the Quran produces significant relaxation because it has specific effects on the human heart that may cause some hormones and chemicals to respond towards relaxation[28].

According to Nivethitha et al[29], slow deep breathing can give a therapeutic effect on autonomic tone. Slow breathing is believed to lower the basal heart rate, the heart rate when a person awakens[30]. They also stated that regular practice of slow breathing exercise improves autonomic functions compared to fast breathing exercise. Furthermore, slow breathing suppresses adrenal medullary secretion of norepinephrine and sympathetic excitement[31]. Meanwhile, Narkiewicz et al[32] mentioned that rapid breathing will lead to sympathetic activation. Higher respiratory rates are associated with increased levels of sympathetic traffic and the potential of chemoreceptor responses to hypoxia and hypercapnia.

To differentiate autonomic activation separately, we assumed the HF values for the parasympathetic action. Analysis of the HF showed a low HF reading for both groups across the three tasks, with one exception for the non-Tahfiz group during Task 3. During recalling of newly memorised verses, the non-Tahfiz group exhibited a higher parasympathetic action as a reflection of calmness during Task 3. A similar study also found that the effect of Quran recitation gave an even ECG reading, suggesting a calming state[13]. Compared to the Tahfiz group, the non-Tahfiz group memorised fewer verses, hence allowing them to recall the same verses repeatedly. On the other hand, the Tahfiz group who memorised more verses were more inclined to be nervous as they were used to recall up to three pages during school[33], thus giving a low HF value.

To evaluate the sympathetic action, the LF/HF ratio was also determined, and the results revealed a significant difference between the Tahfiz and the non-Tahfiz groups. The Tahfiz group showed significantly higher readings for all of the tasks given, reflecting the increase in stress and pressure during the memorisation test. One of the inauguration techniques used in Tahfiz schools was the memorisation final examination[34]. Because the Tahfiz students were used to it, exam-induced stress increased during the memorisation test[35], hence giving a high LF/HF ratio. However, frequent examinations allow the cardiovascular system to adapt to the exam-induced stress[7]. The final examination for memorisation that is required for the students could help their cardiovascular system to adapt to the pressure. Another study also proved that having enough stress was vital in athletes’ physiological adaptation, which led to positive health effects later in their life[36]. Hence, similar positive outcomes could also be expected and observed among students memorising Quranic verses. For other study, it is found that non-experienced students on laboratory practice showed a maintained sympathetic modulation while experienced students presented a higher parasympathetic modulation[37]. Meanwhile, high performance chess players showed a reduced autonomic modulation during difficult chess endgames which low performance players did not reach[38].

The stress and pressure experienced by the Tahfiz students also increased proportionately to the number of pages memorised. The positive correlation between the number of pages memorised and the LF/HF ratio showed that sympathetic action increased with the number of pages memorised (which is another form of mental pressure)[36]. Therefore, memorisation of the Quran could increase the HRV and thus, could also give beneficial effects to the cardiovascular system in the long run. These findings suggest the probable benefits of Quran memorisation towards the autonomic responses. It also provides a new perspective on Quran memorisation in therapeutic applications.

The current study was limited by the recruitment of students from different types of schools. No doubt, they experience different environments and different methods of memorising. All of these differences could contribute to the different impacts on physiological responses, including the HRV. Even though we aimed to have a logically assumed representation of samples by employing the purposive sampling to choose the schools in our study, we acknowledge the possible biases that arose from this approach. However, we tried to minimise it by randomly recruiting students from the selected schools. Future studies could perhaps employ random sampling at all stages. It is also suggested for prospective studies to compare the effect of Quran memorisation with other written texts in the future.

CONCLUSION

The process of Quran memorisation increased the HRV in several ways. It activates both sympathetic and parasympathetic actions with the increase of SDNN and LF values. Besides that, the process of memorisation itself could also induce stress as the LF/HF ratio increased. However, the HF value only increased during the process of recalling memorised verses, indicating an increase in the level of calmness. Hence, even with a high sympathetic modulation during memorisation, it is believed to modulate the sympathovagal activities in the long run.

ACKNOWLEDGEMENTS

The author would like to thank the Tahfiz and Health Research Team from the Faculty of Health Sciences, Universiti Kebangsaan Malaysia, for their contribution during data collection.