Comparison of Heart Rate Variability and Heart Rate Recovery Indices in Healthy Young Adults after Submaximal Exercise with and without Music Intervention

Introduction

Physical exercise is a condition that places high functional demand on the cardiovascular system. It is associated with increased sympathetic activity, and suppression of parasympathetic activity, resulting in increased heart rate (HR). The increased HR rapidly decreases after cessation of exercise. This rapid HR recovery is essential in preventing excessive cardiac strain after exercise. Parasympathetic reactivation and sympathetic withdrawal after the exercise decreases the heart rate. Thus, post-exercise parasympathetic reactivation appears to be a significant mechanism with a cardioprotective effect.¹

Heart Rate Variability (HRV) is a useful application in assessing autonomic modulation. HRV is used to measure the sympathovagal balance of the body. The High Frequency (HF) component indicates the parasympathetic zone while the Low Frequency (LF) component indicates the sympathetic function. LF/HF indicates the sympatho-vagal balance.² An attenuated heart rate recovery (HRR) immediately after exercise, is a marker of reduced parasympathetic activity. Hence, HRR is another tool for assessing the autonomic status.³

Research indicates that music can effectively modulate emotions and autonomic nervous system activity and is potentially a cost-effective and safe adjuvant for intervention and therapy. In young adults, calming music is known to induce deep relaxation and reduce tension, on a subjective level.¹

The benefits of music intervention during and after exercise have been explored in earlier studies, with varying results. Jain JK and Maheshwari R reported in their study that HRV pattern showed increased parasympathetic and decreased sympathetic activity while listening to Indian classical music versus pop music and no music.⁴ Niu M et al., in their randomized controlled study, involving 180 young athletes performing high-intensity exercise on power cycle, followed by exposure to music in different tempos in the post-exercise period, found no difference in HRV parameters in any cohort, but the subjects who listened to fast-tempo music showed a significant heart rate recovery (HRR) than the groups that listened to slow-tempo music, medium-tempo music, or no music.⁵ Desai et al., studied the effect of music on post-exercise recovery in young, healthy individuals. They found that slow music significantly improved recovery of physiological parameters compared to both no music and fast music.⁶ However, across studies, the characteristics of music such as melody, tempo, and volume, as well as listener characteristics such as music training, music appreciation, music preference, etc, have been found to influence the effect on HRV and HRR.^1,7

The present study intended to explore the effect of music intervention on heart rate variability and heart rate recovery in healthy young adults after submaximal exercise, which is more akin to daily activities of life. It also purports to test whether this influence occurs irrespective of listener characteristics mentioned above.

Objectives of the study

1) To compare Heart Rate Variability (HRV) and Heart Rate Recovery Indices (HRRI) after submaximal exercise in young adults, with and without post-exercise music intervention.

2) To evaluate the effect of music intervention on cardiac autonomic modulation after exercise.

Materials and Methods

This was an interventional study with pre-post comparison design. The study was commenced after obtaining clearance from the Institutional Ethics Committee. Healthy young adult male participants were enlisted through voluntary participation, as per the following criteria:

Inclusion criteria

• Subjects of either gender, in the age group of 18-25 years.

• Subjects willing to give written informed consent.

Exclusion criteria

• Patient not willing to give consent

• Subjects already doing strenuous exercise/ work out on a regular basis

• Subjects who are regularly practicing or involved in sports activities

• Subjects with diabetes mellitus, hypertension, or other significant systemic illness

• Pregnancy

• History of cardiorespiratory illness

• History of regular consumption of medication for any chronic illness

• History of substance abuse/dependence

• Neuromuscular disorders or skeletal deformities

• Other conditions that preclude exercise testing

Based on a previous study by Jia et al., pre and post-intervention HR in the music therapy group was 75.8 ±1.8 and 74.1±2.0.¹ The sample size was estimated using the formula n = 2* (Zα/2 + Z 1-β) * σ^2 / d^2, for a confidence interval of 99% and power of 90%, to detect an effect size of 0.89. On adding 10% to account for loss to follow-up, the estimated sample size required was 21.

Each participant was explained the study procedure and objectives. Written informed consent was taken. A detailed history was taken including personal history, history of medical illnesses, treatment, and medication history. A thorough clinical examination was done to rule out any abnormalities. Conformity with inclusion/exclusion criteria was confirmed and the final study sample of 21 participants was formed. On the first day, the participants were invited to the research lab and allowed to rest for 10 minutes in supine posture and the baseline recordings of heart rate, blood pressure, and respiratory rate were measured following standard procedure. A five-minute recording of resting HRV was taken using AD Instruments PowerLab 15T 16-channel polygraph, by connecting ECG electrodes and obtaining lead II ECG. The data was analysed using Lab Chart 8 software, to obtain the time domain (Mean RR, SDNN, RMSSD, pNN50) and frequency domain (TP, LFnu, HFnu, LF/HF) measures of HRV. The participants were instructed to perform a 6-minute walk test as per the standard protocol of the American Thoracic Society.8 It involves the subject walking at a comfortable pace in a corridor for six minutes. This is a standard procedure to induce submaximal exercise conditions. Immediately following the exercise period, peak HR was noted, the subject was allowed to rest in supine position, and HRV was recorded for five minutes. HR at 1 minute and 3 minutes after exercise were noted. HRRI was calculated as detailed below.

On the intervention day, the same procedure was repeated. Immediately after finishing the 6-minute walk test, the subject was made to listen to music (veena rendition in raaga Naata, at madhyamagati, i.e., moderate tempo) for five minutes, using a mobile phone and headset, in supine position, in a soundproof room of the research lab. The music played, its tempo, and volume were standardized for all subjects. As the subject listened to music, HRV was recorded and HRRI was calculated as above.

Measurement of HRRI

Heart Rate Recovery Indices HRRI1 and HRRI3

1. HRRI1 = HR immediately after exercise - HR at 1 min after the end of the exercise.

2. HRRI3 = HR immediately after exercise- HR at 3 min after the end of the exercise.

Statistical analysis was done using an open-source computer software, Jamovi (Version 2.4), which uses the programming language R (Version 4.1). Tables and graphs were created using Jamovi, Microsoft Excel and Microsoft Word. Descriptive statistics for continuous variables are represented as Mean±Standard Deviation. For hypothesis evaluation, P <0.05 was considered statistically significant. Repeated measures ANOVA was used to compare HRV parameters at baseline and the two tests. Paired samples Student’s t test was used to compare means of HRR between two study conditions.

Results

The study included 21 male participants with a mean age of 18.86 ± 0.56 years. None of the HRV parameters showed a significant difference between any of the three test conditions – baseline, after walk and without music, after walk and with music (P > 0.05). HRRI1 was found to be significantly higher with music (14.19 ± 2.015) as compared to without music (12.571 ± 2.694) (P < 0.001). HRRI3 was also found to be significantly higher with music (43.857 ± 5.918) as compared to without music (39.476 ± 7.38) (P = 0.01).

Discussion

Our study found no significant variations in the recorded HRV parameters in different test conditions. Many authors have reported a shift to parasympathetic activity in HRV while listening to music, while some have not. Systematic reviews have opined that absence of impact of music on HRV in studies can be due to small sample size, concise duration of music administration, and other music related factors such as genre, melody, tempo, and volume.⁹ Although our methodology standardized the music related factors, our results are still limited by sample size and intervention duration. These results must hence be reexamined with a larger sample size and with a longer duration of exposure to music. Earlier studies have also shown varied results due to listener characteristics such as prior music training, music appreciation, and genre preference. Archana R et al., showed that listening to preferred music after exercise activates the parasympathetic system more than when listening to non-preferred music.¹⁰ As our study standardized the music used, the effect of personal preference could not be accounted for. Further studies can be undertaken to factor in participant preferences in the effect produced.

Although HRV parameters showed no significant variations, the parasympathetic stimulatory effect of music was evident in the heart rate recovery indices assessed. Heart rate recovery post exercise was significantly faster when listening to music than without listening to music. Heart rate recovery at one minute and three minutes after exercise was significantly greater with music intervention than without. Our findings are in line with those of Niu M et al., and Desai R et al., who concluded that listening to music improved heart rate recovery indices after exercise.^5,6 The difference in HRRI1 was higher than the difference in HRRI3 between the two test conditions. This confirms our hypothesis that music might cause immediate and sustained parasympathetic activation leading to quicker heart rate recovery. It is noteworthy that this effect was found irrespective of listener’s characteristics including genre preference.

Conclusion

Music intervention post-exercise enhances the heart rate recovery rate. Thus, it can be a useful adjunct to hasten recovery and minimize the workload on the heart after exercise.

Based on our findings, we recommend listening to music after exercise to gain the added benefit of enhanced recovery. Studies with a larger sample size, longer duration of exposure to music, and administration of music based on participant preference must be undertaken to further investigate in detail the effects of music on the autonomic nervous system and heart.