European Journal of Cardiovascular Medicine

Nutritional status plays a fundamental role in maintaining optimal physiological function and overall health. Adequate nutrition is essential for maintaining metabolic homeostasis, cardiovascular stability, neuromuscular performance, and autonomic nervous system balance. Both undernutrition and overnutrition have been shown to influence cardiovascular regulation and muscular performance, particularly in young adults whose physiological systems are still adapting to lifestyle and metabolic demands. Consequently, evaluating the relationship between nutritional status and physiological parameters such as heart rate variability (HRV) and skeletal muscle endurance provides important insights into the functional consequences of nutritional imbalance.¹

Heart rate variability refers to the beat-to-beat variation in heart rate and is considered a non-invasive marker of autonomic nervous system activity, reflecting the balance between sympathetic and parasympathetic influences on the heart. Reduced HRV is associated with autonomic dysfunction and has been linked to increased cardiovascular risk, metabolic disorders, and impaired physiological resilience. Nutritional deficiencies, particularly those involving micronutrients, energy intake, and body composition alterations, can significantly affect autonomic regulation and thereby influence HRV. Previous studies have demonstrated that malnutrition and altered body mass index (BMI) are associated with impaired vagal activity and increased sympathetic dominance, resulting in reduced HRV indices.²

Skeletal muscle endurance, defined as the ability of muscle groups to sustain repeated contractions or maintain contraction over time, is another physiological parameter strongly influenced by nutritional status. Adequate intake of macronutrients such as proteins and carbohydrates, along with essential micronutrients, is necessary for muscle metabolism, mitochondrial function, and energy production. Poor nutritional status may lead to decreased muscle mass, impaired energy metabolism, and reduced muscular endurance. Conversely, optimal nutritional status contributes to improved muscular performance and functional capacity.³

Young adulthood represents a critical period characterized by rapid lifestyle changes, dietary transitions, and varying levels of physical activity. In many developing countries, including India, young adults may experience both undernutrition and emerging trends of overweight and obesity. These nutritional variations can significantly affect cardiovascular autonomic regulation and skeletal muscle performance, yet the relationship between these variables remains inadequately explored in this population.⁴

Recent research has increasingly emphasized the importance of HRV as an early indicator of cardiovascular health and autonomic balance. Similarly, skeletal muscle endurance is a key determinant of physical fitness and metabolic health. Despite the independent significance of these parameters, limited studies have simultaneously examined their relationship with nutritional status in young adults. Understanding these associations may help identify early physiological alterations related to poor nutrition and guide preventive strategies aimed at improving cardiovascular and musculoskeletal health.⁵

Therefore, assessing the impact of nutritional status on HRV and skeletal muscle endurance may provide valuable insights into the functional implications of nutrition in apparently healthy individuals. Such information is important for developing health promotion strategies, improving physical performance, and preventing long-term cardiovascular and metabolic complications.⁶

Aim

To study the effect of nutritional status on heart rate variability and skeletal muscle endurance in young adults.

Objectives

1. To assess the nutritional status of young adults using anthropometric parameters such as body mass index (BMI).
2. To evaluate heart rate variability as an indicator of autonomic nervous system function.
3. To assess skeletal muscle endurance using standardized muscle endurance tests.
4. To determine the relationship between nutritional status and heart rate variability.
5. To analyze the association between nutritional status and skeletal muscle endurance in young adults.

Justification for the Study

Nutritional status significantly influences cardiovascular autonomic regulation and muscular performance, both of which are critical indicators of overall physiological health. Heart rate variability is widely recognized as a sensitive marker for autonomic balance and early cardiovascular risk, while skeletal muscle endurance reflects functional muscular capacity and metabolic efficiency. However, there is limited literature examining the combined relationship between nutritional status, HRV, and skeletal muscle endurance in young adults. With changing dietary patterns and sedentary lifestyles among the youth, understanding these associations is essential for early identification of physiological impairments related to malnutrition or poor dietary habits. The findings of this study may contribute to improved awareness regarding the importance of adequate nutrition in maintaining autonomic and muscular health and may help guide preventive health strategies among young adults.

Study Design The present study was conducted as a cross-sectional observational study to evaluate the effect of nutritional status on heart rate variability and skeletal muscle endurance in young adults. Place of Study The study was carried out in the Department of Physiology, Konaseema Institute of Medical Sciences, Amalapuram, Andhra Pradesh, India. Duration of Study The study was conducted over a period of 11 months from December 2021 to October 2022. Study Population The study population consisted of young adult volunteers aged between 18 and 25 years, primarily undergraduate medical students of Konaseema Institute of Medical Sciences who consented to participate in the study. Sample Size A total of 120 participants were included in the study. Participants were categorized into groups based on their nutritional status determined by Body Mass Index (BMI) according to World Health Organization (WHO) classification. Sampling Method Participants were selected using simple random sampling from the eligible student population after obtaining informed consent. Inclusion Criteria • Healthy young adults aged 18–25 years. • Individuals willing to participate and provide written informed consent. • Participants without any known acute or chronic illness. Exclusion Criteria • Individuals with history of cardiovascular disease, respiratory disorders, neuromuscular disease, or metabolic disorders. • Subjects taking medications affecting cardiovascular or autonomic function. • Individuals involved in regular intensive athletic training. • Participants with history of smoking or alcohol dependence. • Subjects with acute illness at the time of examination. Ethical Considerations The study protocol was reviewed and approved by the Institutional Ethics Committee of Konaseema Institute of Medical Sciences, Amalapuram. Written informed consent was obtained from all participants prior to enrollment in the study. Assessment of Nutritional Status Nutritional status was assessed using anthropometric measurements, including height and weight. • Height was measured using a stadiometer to the nearest 0.1 cm with participants standing barefoot. • Weight was measured using a calibrated digital weighing scale to the nearest 0.1 kg. Body Mass Index (BMI) was calculated as weight in kilograms divided by the square of height in meters 〖"kg/m" 〗^2. Participants were then classified according to the WHO BMI criteria into underweight [<18.5 kg/m²], normal weight [18.5-24.9 kg/m²], overweight [25.0-29.9 kg/m²], and obese [≥30.0 kg/m²]. Assessment of Heart Rate Variability (HRV) Heart rate variability was recorded using a standard digital electrocardiography (ECG) system in the Physiology laboratory under controlled environmental conditions. Participants were instructed to: • Avoid caffeine, heavy meals, and vigorous exercise for 12 hours prior to testing. • Rest quietly for 10 minutes before the recording. A 5-minute resting ECG recording was obtained in the supine position. HRV parameters were analyzed using HRV analysis software. The following parameters were evaluated: Time domain parameters • Mean heart rate • SDNN (Standard deviation of NN intervals) • RMSSD (Root mean square of successive differences) Frequency domain parameters • Low frequency (LF) • High frequency (HF) • LF/HF ratio Assessment of Skeletal Muscle Endurance Skeletal muscle endurance was assessed using standardized isometric endurance tests. 1.Hand Grip Endurance Test Hand grip strength was measured using a hand grip dynamometer. Participants were asked to maintain one-third of their maximum voluntary contraction for as long as possible. The time (in seconds) for which the contraction could be sustained was recorded as the hand grip endurance time. 2.Static Squat Test (Wall Sit Test) Participants were asked to maintain a sitting position against a wall with knees flexed at 90°. The duration for which the position could be maintained was recorded in seconds and considered as an indicator of lower limb muscle endurance. Data Collection Procedure All measurements were conducted in the morning hours between 9 AM and 11 AM to minimize circadian variations. Participants were allowed adequate rest between tests to prevent fatigue. All measurements were recorded by trained personnel in the Physiology laboratory. Statistical Analysis Data were entered into Microsoft Excel and analyzed using Statistical Package for Social Sciences (SPSS) version 25.0. o Quantitative data were expressed as mean ± standard deviation (SD). o Comparison between BMI groups was performed using one-way ANOVA. o Association between nutritional status, HRV parameters, and skeletal muscle endurance was assessed using Pearson’s correlation coefficient. o A p value <0.05 was considered statistically significant.

A total of 120 young adults aged between 18 and 25 years participated in the study. Participants were categorized based on Body Mass Index (BMI) into underweight, normal weight, and overweight groups according to the WHO classification. The results of the study are presented below.

Table 1: Distribution of Participants According to Nutritional Status (BMI)

The majority of participants (53.3%) belonged to the normal BMI group, while 23.3% were underweight and 23.3% were overweight.

Table 2: Comparison of Heart Rate Variability Parameters Among BMI Groups

Participants with normal BMI demonstrated significantly higher HRV parameters (SDNN, RMSSD, HF power) compared to underweight and overweight individuals, indicating better autonomic balance and parasympathetic activity.

Table 3: Comparison of Skeletal Muscle Endurance Among BMI Groups

Skeletal muscle endurance was significantly higher in individuals with normal BMI compared to underweight and overweight groups.

Table 4: Correlation Between BMI and HRV Parameters

A moderate positive correlation was observed between BMI and HRV parameters such as SDNN and RMSSD, indicating that individuals with better nutritional status tend to have improved autonomic regulation.

Table 5: Correlation Between BMI and Skeletal Muscle Endurance

A significant positive correlation was observed between BMI and skeletal muscle endurance, suggesting that nutritional status influences muscular performance.

The present study was conducted to evaluate the effect of nutritional status on heart rate variability (HRV) and skeletal muscle endurance in young adults. Nutritional status plays a significant role in maintaining cardiovascular autonomic regulation and muscular performance. The findings of the present study demonstrated that individuals with normal body mass index (BMI) exhibited significantly better HRV parameters and skeletal muscle endurance compared to underweight and overweight individuals.

In the present study, participants with normal BMI showed higher SDNN and RMSSD values, indicating greater parasympathetic activity and better autonomic balance. HRV is widely recognized as a non-invasive marker for evaluating cardiac autonomic function. Reduced HRV has been associated with autonomic imbalance and increased cardiovascular risk. The Task Force of the European Society of Cardiology has established HRV as an important indicator of autonomic nervous system activity and cardiovascular regulation.⁷

Similarly, Thayer and Lane reported that decreased vagal tone and reduced HRV are associated with higher risk of cardiovascular morbidity and mortality.⁸ These findings support the results of the present study, which showed improved HRV parameters in individuals with optimal nutritional status.

The present study also demonstrated that underweight individuals had lower HRV values, suggesting reduced parasympathetic activity and possible autonomic dysfunction. Malnutrition may influence autonomic function by affecting metabolic and hormonal regulation. Peterson et al. reported that variations in body fat and nutritional status can significantly alter autonomic nervous system activity, leading to reduced HRV.⁹

Overweight participants in the present study also showed relatively lower HRV compared to individuals with normal BMI. Increased adiposity has been associated with sympathetic overactivity and decreased parasympathetic modulation. Tentolouris et al. demonstrated that obesity is associated with impaired autonomic nervous system function and reduced HRV parameters.¹⁰ Similarly, Karason et al. reported that HRV improves following weight reduction, indicating the influence of body composition on autonomic regulation.¹¹

In addition to autonomic function, the present study evaluated skeletal muscle endurance using hand grip endurance and wall sit tests. The results indicated that participants with normal BMI had significantly higher muscle endurance compared to underweight and overweight groups. Adequate nutrition is essential for maintaining muscle mass, energy metabolism, and mitochondrial efficiency, all of which are necessary for sustained muscular activity.

Underweight individuals in the present study demonstrated reduced muscle endurance, which may be attributed to decreased muscle mass and lower energy reserves. Nutritional deficiencies may impair muscle protein synthesis and reduce functional muscle capacity. Wolfe emphasized that skeletal muscle plays a crucial role in metabolic health and physical performance, and inadequate nutrition may impair muscle function.¹²

Similarly, overweight individuals also demonstrated reduced endurance compared with those having normal BMI. Excess adipose tissue increases mechanical load during physical activity and may reduce muscular efficiency. McArdle et al. reported that body composition and nutritional status significantly influence muscle performance and endurance capacity.¹³ Furthermore, Hills and Byrne highlighted that increased body fat can negatively affect physical performance and functional capacity.¹⁴

The correlation analysis in the present study showed a positive association between BMI and HRV parameters, suggesting that optimal nutritional status contributes to better autonomic regulation. A positive correlation was also observed between BMI and skeletal muscle endurance, indicating that adequate nutrition plays a significant role in maintaining muscular performance.

Young adulthood is an important period during which lifestyle factors such as dietary habits, physical activity, and stress can influence long-term health outcomes. With the increasing prevalence of both undernutrition and obesity among young adults, evaluating the physiological effects of nutritional imbalance becomes important. Booth et al. emphasized that inadequate physical activity and poor lifestyle behaviors are major contributors to chronic diseases affecting cardiovascular and metabolic health.¹⁵

The findings of the present study highlight the importance of maintaining optimal nutritional status for proper autonomic function and muscular endurance. Balanced diet, regular exercise, and healthy lifestyle practices may improve HRV and skeletal muscle endurance, thereby reducing the risk of cardiovascular and metabolic disorders.

However, the present study has certain limitations. The sample size was relatively small and limited to a single institution, which may affect generalizability. In addition, nutritional assessment was based only on BMI, which does not fully reflect body composition. Future studies incorporating dietary analysis, body fat percentage, and biochemical nutritional markers may provide a more comprehensive understanding of the relationship between nutrition, autonomic function, and muscular endurance.

The present study evaluated the effect of nutritional status on heart rate variability (HRV) and skeletal muscle endurance in young adults. The findings demonstrated that individuals with normal body mass index (BMI) exhibited significantly better HRV parameters, indicating improved autonomic nervous system balance, compared to underweight and overweight individuals. Additionally, skeletal muscle endurance assessed by hand grip endurance and wall sit tests was significantly higher in participants with normal BMI. Both undernutrition and excess body weight were associated with reduced HRV and lower muscular endurance, suggesting that deviations from optimal nutritional status may negatively influence cardiovascular autonomic regulation and physical performance. These findings highlight the important role of balanced nutrition in maintaining autonomic stability and muscular function in young adults. Therefore, maintaining an optimal nutritional status through balanced diet and healthy lifestyle practices may contribute to improved cardiovascular health and muscular performance, and may help in preventing future metabolic and cardiovascular disorders.

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