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PhysiologiaPhysiologia
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30 January 2026

Gender Differences in Autonomic Stress Status and Body Fat Percentage Among Teachers

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and
1
Department of Nursing, Faculty of Medicine, Health and Sport, Universidad Europea de Madrid, 28670 Madrid, Spain
2
Department of Pharmacy and Nutrition, Faculty of Medicine, Health and Sport, Universidad Europea de Madrid, 28670 Madrid, Spain
3
Research Group on Culture, Education and Society, Universidad de la Costa, Barranquilla 080002, Colombia
*
Author to whom correspondence should be addressed.
Physiologia2026, 6(1), 10;https://doi.org/10.3390/physiologia6010010
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Abstract

Background/Objectives: Teaching is a profession characterized by a high burden of stress. This study examined sex differences in autonomic regulation by analysing heart rate variability (HRV) and body fat percentage (BF%) in teachers, explicitly hypothesizing that the association between adiposity and autonomic modulation (HRV) would be more consistent in men. Methods: A cross-sectional study was conducted with 253 teachers from compulsory and university education during the 2022–2023 academic year. HRV was obtained from heart rate recordings, and body composition was assessed using bioelectrical impedance analysis. Analyses were stratified by sex and, in addition to comparisons based on the sex-specific median of fat mass (kg), ANCOVA models were performed and adjusted for age, teaching experience, and educational level. Results: Teachers with higher BF% were older (43.46 vs. 40.65 years; p = 0.007) and reported higher perceived stress (7.60 vs. 6.83; p = 0.034). In men, HRV was lower in the ≥p50 adiposity group, with reductions in RMSSD and pNN50 (p = 0.015–0.016). In women, RMSSD and pNN50 were not significant (p > 0.20; small effect sizes). In adjusted analyses (ANCOVA), no significant differences were found in men for any index; in women, HRmax and the LF/HF ratio were significant (small effects), whereas the remaining indices were not. Conclusions: Greater adiposity was associated with higher stress and lower HRV, particularly in men. In women, the pattern was more heterogeneous, and significance after adjustment was limited to HRmax and the LF/HF ratio, suggesting the need for sex-specific approaches to the assessment and promotion of psychophysiological well-being in teachers.

1. Introduction

Prolonged exposure to stress can disrupt the principal neuroendocrine regulatory axes, such as the hypothalamic–pituitary–adrenal (HPA) axis. This disruption can trigger glucocorticoid signaling that promotes central fat accumulation and the emergence of cardiometabolic alterations associated with autonomic dysfunction [1,2,3]. Consequently, stress plays a crucial role in the development and progression of overweight and obesity, which in turn contribute to the onset of chronic conditions such as diabetes and mental health disorders [1].
Teaching involves an intense and sustained psychosocial burden, placing this workforce among those with the greatest exposure to occupational stressors [4,5]. In this context, stress arises when environmental demands are perceived as threats to professional efficacy or personal well-being. This situation activates coping mechanisms that, when sustained over time, can compromise physical and emotional health [4,6]. The principal biological responses involved include activation of both the HPA axis and the sympathetic nervous system (SNS), central modulators of physiological homeostasis through the release of cortisol and catecholamines [6,7].
The autonomic nervous system (ANS), comprising the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS), regulates the body’s responses to internal and external stimuli [8]. In the presence of demand, sympathetic responses predominate (tachycardia, increased blood pressure and ventilation), whereas in resting contexts vagal modulation prevails, facilitating recovery and energy conservation [2,6,7]. This dynamic balance underpins autonomic homeostasis [3].
Heart rate variability (HRV) is considered a sensitive, noninvasive marker of autonomic modulation [9]. It has also been proposed as an indicator of adiposity in various studies [10]. Sustained sympathetic activation tends to homogenize R–R intervals (lower variability), whereas vagal influence promotes rapid, respiration-dependent fluctuations. Within this framework, low HRV is associated with reduced physiological flexibility and poorer adaptive capacity, whereas higher values reflect greater self-regulatory capacity [8]. Complementarily, low HRV has been associated with obesity, metabolic syndrome, and related conditions [11,12]. In this regard, elevated adiposity may act as a marker of autonomic dysfunction [13].
Sex-stratified analyses are essential to avoid misleading interpretations and to detect differential patterns, given the marked sexual dimorphism in body composition, hormonal profiles, and autonomic organization. Recent evidence shows sex-specific divergences in both HPA-axis dynamics and autonomic modulation, including variations in glucocorticoid secretion and HRV indices, as well as the influence of gender-related factors linked to roles, workloads, and psychosocial demands. Meta-analyses based on 24-h recordings report particularly pronounced differences in nocturnal vagal indices, reinforcing the need for sex-differentiated analyses [14,15].
In the educational context, recent studies have confirmed the usefulness of HRV for characterizing teacher stress. Ambulatory measurements during the working day show increases in heart rate, decreases in HRV, anticipatory responses before class onset, and insufficient midday recovery [16,17]. Moreover, factors such as student aggression or a high load of frontal teaching are associated with lower HRV, whereas a more positive teacher–student relational climate is linked to higher values [16]. Gender differences have also been described: despite reporting higher perceived stress, women may exhibit higher resting vagal values, suggesting distinct physiological profiles [16,18]. A recent review in Educational Psychology Review further synthesizes key methodological recommendations for HRV research in educational settings, emphasizing the need to standardize parameters, recording duration, and artifact correction [19].
Investigating stress levels and HRV in teachers across different educational stages, as well as their relationship with body fat percentage, is particularly relevant given the high workload, administrative demands, student behavior, and the challenges of balancing personal and professional life [20]. Recent literature highlights the intensification of teaching work and the resulting “time poverty,” phenomena that have a documented impact on health and teacher retention. These factors may act as confounders in the association between adiposity and autonomic modulation [21,22].
The aim of this study was to analyze gender differences in autonomic stress status through the assessment of HRV and body fat percentage in teachers. To capture the heterogeneity of demands across educational levels, a mixed sample of compulsory-education and university teachers was included. Analyses were conducted stratified by sex and adjusted for variables such as age, teaching experience, and educational level [21]. In addition, the most current methodological recommendations for HRV research were followed to ensure the comparability of measurements [19].
Given these differences, we adopted a sex-specific analytical approach and, based on previous evidence, hypothesized that female teachers would exhibit higher resting HRV values and differential patterns of autonomic modulation compared with their male counterparts. These differences may be influenced by physiological factors such as adipose tissue distribution or hormonal profiles, which are particularly relevant in professions exposed to sustained psychosocial stressors. Identifying these patterns is essential for developing targeted preventive strategies aimed at improving teacher well-being and reducing the risks associated with chronic stress, thereby justifying the relevance and specific focus of the present study [14,17,18,19].

2. Results

2.1. Characteristics of Survey Respondents

Table 1 presents the characteristics of the sample, classified into two groups based on the 50th percentile (p50) of body fat (kg). A total of 35.70% (n = 90) of the sample was classified as overweight or obese according to body mass index (BMI) (>25 kg/m2), with a significantly higher prevalence in men than in women (40.30% vs. 31.60%; p = 0.039; proportion comparison using χ2 or Fisher’s exact test when appropriate). When classifying the sample according to adiposity level using Siri’s cut-off points [23], 53.60% showed excess body fat, with no significant sex differences (men: 47.80% vs. women: 55.90%; p = 0.260; χ2 proportion comparison). Additionally, to facilitate the clinical interpretation of the key comparisons reported in Section 2.1, effect size estimates are provided alongside p-values in the corresponding subsections (e.g., Cohen’s d or r), as specified in the statistical procedures.
Table 1. Characteristics of Survey Respondents.
The distribution of educational level did not differ between adiposity groups (χ2 = 4.867; p = 0.432), as shown in Table 1.

2.1.1. Teachers’ Age

Significant differences were observed with respect to age. Participants with lower body fat presented a mean age of 40.65 ± 8.93 years, whereas those with higher body fat showed a mean age of 43.46 ± 9.11 years (p = 0.007; d = 0.31, small effect size). Similarly, teachers younger than 43 years (<p50) exhibited significantly lower body fat levels compared with those aged 43 years or older (≥p50), who presented higher adiposity (p = 0.014; χ2 proportion test).

2.1.2. Average Level of Job Satisfaction

The mean level of job satisfaction was 8.04 ± 1.36 on a 0–10 scale, with no significant differences observed between groups (p = 0.456; trivial effect size, d < 0.20).

2.1.3. Self-Perception of Stress Levels

Significant differences were found in perceived stress levels. In the lower-adiposity group, the mean score was 6.83 ± 2.36, whereas in the higher-adiposity group it was 7.60 ± 1.82 (U = 3321.5; p = 0.034; r = 0.16).

2.2. Adiposity Differences in Heart Rate Variability (HRV)

Next, we examined the association between adiposity categories defined by the sex-specific median of fat mass (kg) and HRV parameters, stratifying the results by sex (Table 2 and Table 3). For each comparison, the p-value is reported alongside the corresponding effect size (Cohen’s d or r, as appropriate), applying parametric or non-parametric tests depending on the fulfillment of normality assumptions, as detailed in the Statistical Procedures section.
Table 2. Adiposity Differences in Heart Rate Variability (HRV) in Men.
Table 3. Adiposity Differences in Heart Rate Variability (HRV) in Women.

2.2.1. HRV in Men

In men (Table 2), significantly higher mean and minimum heart rate values were observed in the group with a higher percentage of body fat (BF%). Specifically, mean heart rate was 73.14 ± 8.51 compared with 67.97 ± 11.78 (U = 359.0; p = 0.045; r = 0.40, moderate effect), and minimum heart rate was 63.10 ± 6.84 compared with 57.68 ± 10.00 (U = 316.5; p = 0.014; r = 0.47, moderate effect). No association between heart rate and BF% was found in women.
For the Root Mean Square of Successive Differences (RMSSD) and the Percentage of NN intervals that differ by more than 50 ms (pNN50), significant differences were identified in men, with lower values in the higher-BF% group, indicating reduced HRV or increased sympathetic activation (RMSSD: 34.75 ± 14.49 vs. 47.25 ± 26.75, p = 0.015; d = 0.53, moderate effect; pNN50: 12.31 ± 10.50 vs. 21.28 ± 17.96, p = 0.016; d = 0.42, moderate effect). No differences were found in the LF/HF ratio; however, Standard Deviation 1 (SD1) and Standard Deviation 2 (SD2) values were significantly lower in the higher-BF% group, consistent with reduced parasympathetic activity and in line with the RMSSD results (SD1: p = 0.015; d = 0.53, moderate effect; SD2: p = 0.009; d = 0.45, moderate effect).

2.2.2. HRV in Women

In women, contradictory results were observed. Although RMSSD and pNN50 values were also lower in the higher-BF% group, these differences did not reach statistical significance (RMSSD: 56.21 ± 44.54 vs. 61.51 ± 53.44, p = 0.264; d = 0.27, very small effect; pNN50: 19.40 ± 18.83 vs. 22.19 ± 20.80, p = 0.202; d = 0.22, very small effect).
Regarding the Low-Frequency Power (LF) and High-Frequency Power (HF) components in the frequency domain, as well as the LF/HF ratio, significant results were found that contradicted the previous HRV findings, suggesting greater sympathetic predominance in the lower-BF% group (LF/HF: 3.13 ± 2.60 vs. 2.42 ± 2.33, p = 0.015; U = 3231.0; r = 0.23, small effect).
Consistently, the higher-BF% group showed lower LF (62.98 ± 14.94 vs. 68.37 ± 13.25, p = 0.014; U = 3228.5; r = 0.23, small effect) and higher HF (36.90 ± 14.95 vs. 32.57 ± 14.60, p = 0.015; U = 3233.0; r = 0.23, small effect), reinforcing the LF↓/HF↑/LF/HF↓ pattern in the ≥p50 group.
Finally, differences were identified in maximum heart rate, with lower values in the higher-BF% group (100.83 ± 26.28 vs. 107.10 ± 32.01, p = 0.033; U = 2649.0; r = 0.37, moderate effect).
This frequency pattern was maintained, at least partially, after adjusting for age, teaching experience, and educational level: in the ANCOVA models for women, the difference in the LF/HF ratio was confirmed (small effect), whereas LF and HF only showed nonsignificant trends. Additionally, maximum HR remained significantly lower in the group with higher %BF (small effect).
Given the well-known limitations of interpreting the LF/HF ratio as a direct reflection of sympathovagal balance, and the absence of respiratory recordings and baroreflex sensitivity in our design, the frequency-domain differences should be interpreted with caution. This recommendation aligns with recent methodological guidelines for HRV research in educational settings [19].

2.2.3. Sex-Stratified Integrated Analyses and Robustness After Covariate Adjustment

In men, the higher-BF% (≥p50) group showed a consistent profile of lower HRV, with higher mean and minimum heart rate (moderate effects, r ≈ 0.40–0.47) and small-to-moderate reductions in RMSSD, pNN50, SD1, and SD2 (d ≈ 0.42–0.53), suggesting parasympathetic withdrawal and/or greater sympathetic activation associated with elevated adiposity.
In women, vagally mediated time-domain indices (RMSSD and pNN50) were slightly lower in the ≥p50 group, although non-significant and with very small effect sizes (d ≈ 0.22–0.27). In the frequency domain, an LF↓/HF↑/LF/HF↓ pattern was observed, with small effects (r ≈ 0.23), along with lower maximum heart rate in the ≥p50 group (moderate effect, r ≈ 0.37).
Overall, the adiposity–HRV relationship appears more linear and of greater magnitude in men, whereas in women it is more heterogeneous and domain-dependent, with generally small HRV changes.

2.3. ANCOVA Results

Table 4 presents the sex-stratified ANCOVAs comparing groups defined by the sex-specific median of fat mass (kg; valid recordings), adjusted for age, teaching experience, and educational level. For each dependent variable (DV), F(1, dferror), p, and ηp2 are reported.
Table 4. Sex-Stratified ANCOVA of Adiposity and Heart Rate Variability (HRV).
In male teachers, the adjusted ANCOVAs showed no significant differences between <p50 and ≥p50 in any DV (MeanHR, HRminimum, HRmaximum, RMSSD, pNN50, LF, HF, LF/HF, SD1, SD2; all p ≥ 0.217); effect sizes were small (ηp2 ≈ 0.002–0.031).
In women, after adjustment, maximum HR and the LF/HF ratio showed significant differences between <p50 and ≥p50 (HRmax: F(1.118) = 4.762; p = 0.031; ηp2 = 0.039; LF/HF: F(1,118) = 5.528; p = 0.020; ηp2 = 0.045), whereas the remaining dependent variables did not reach statistical significance.

2.4. Linear Regression Models

To evaluate the dose–response relationship between adiposity and HRV, multivariable linear regression models were estimated, stratified by sex, using HRV indices as dependent variables (MeanHR, HRminimum, HRmaximum, RMSSD, pNN50, LF, HF, LF/HF, SD1, and SD2) and body fat percentage (%BF) as the continuous predictor. All models were adjusted for age (years), teaching experience (years), and educational level, applying the same quality filters used in the ANCOVAs. Linearity and homoscedasticity assumptions were verified by residual inspection.
In men, the regression models showed a pattern consistent with the ANCOVA results: the slopes for the vagally mediated time-domain indices (RMSSD, pNN50, and their Poincaré-plot analogues SD1/SD2) were negative and small in magnitude, indicating that higher adiposity was associated with reduced parasympathetic modulation; only SD2 reached statistical significance, whereas the effects on heart rate indices (MeanHR and HRmin) were positive and likewise small. Overall, adjustment for age, teaching experience, and educational level did not modify the direction of the associations, which remained of reduced magnitude.
In women, the associations between %BF and the vagally mediated time-domain indices (RMSSD, pNN50) showed small effects, with pNN50 reaching marginal significance, consistent with the absence of relevant adjusted differences observed in the ANCOVA. In the frequency domain (LF, HF, and LF/HF), the pattern was heterogeneous and characterized by small effect sizes, with no statistical significance for LF/HF, warranting cautious interpretation.
Overall, the regression models did not alter the conclusions derived from the group-adjusted analyses: in men, a weak but systematic association between higher adiposity and lower vagal HRV was observed, whereas in women the associations were generally small; only maximum heart rate and pNN50 showed significant or marginal associations, in line with the results obtained in the ANCOVA analyses.

3. Discussion

The main finding of this study is the identification of a sex-specific pattern in the association between body fat percentage and cardiac autonomic modulation in teachers. In men, an approximately linear relationship is observed, in which greater adiposity is linked to lower HRV, particularly in indices reflecting vagal predominance. In women, however, the relationship is less uniform and appears to depend on physiological mechanisms that operate differently depending on the analytical domain. This pattern, together with the potential intensification of work-related demands in the teaching profession, suggests a more linear profile in men and a more heterogeneous one in women, supporting the need to consider sex-specific intervention strategies.
This interpretation is consistent with recent literature: meta-analyses and reviews describe sex-related differences in HRV (e.g., higher HF and lower LF/HF ratios in women), modulated by age, respiratory control, and recording duration. In addition, 24-h monitoring studies have reported day–night variations that highlight the importance of considering gender-related variables and of reporting respiratory parameters and baroreflex sensitivity in future research [14,24].
Nevertheless, these results should be interpreted with caution, as the cross-sectional design of the study does not allow causal inferences or the determination of the directionality between stress, adiposity, and autonomic nervous system regulation. The observed association may reflect the impact of chronic stress on adiposity and autonomic function. Conversely, it could indicate the influence of greater adiposity on stress levels and autonomic modulation, or a bidirectional process conditioned by unmeasured factors. In this context, the findings are consistent with previous theoretical models proposing a complex, bidirectional interaction between chronic stress, autonomic dysfunction, and body adiposity, without allowing the establishment of a specific temporal sequence based on the available data.
In terms of the magnitude and direction of the effects, men with higher adiposity (≥p50) showed moderate increases in mean and minimum heart rate (r ≈ 0.34–0.40) and moderate reductions in RMSSD, pNN50, SD1, and SD2 (d ≈ 0.58–0.65). In contrast, women exhibited non-significant and very small changes in vagal time-domain indices (d ≈ 0.11–0.14), a small-effect frequency-domain pattern characterized by LF↓/HF↑/LF/HF↓ (r ≈ 0.20), and a moderate decrease in maximum heart rate in those ≥p50 (r ≈ 0.32).
Given that age and teaching experience were significantly associated with body fat percentage, it was necessary to assess their potential role as confounding factors in the relationship between adiposity and HRV. Covariate-adjusted analyses confirmed that the sex-specific pattern observed remained after statistical control, with independent associations between higher adiposity and reduced vagal modulation in men, whereas in women the relationships continued to be more heterogeneous and of smaller magnitude. Consequently, the differences described cannot be explained solely by age or work experience but rather reflect sex-modulated physiological mechanisms.
This discrepancy suggests that the interaction between adiposity and autonomic control does not follow a single physiological model. Instead, it is modulated by sex, fat distribution, and the predominant regulatory systems (vagal, baroreflex, and cardiorespiratory). In line with this, the potential explanations discussed below—including the influence of respiration on HF, baroreflex sensitivity on the LF component, differences in fat distribution (android/gynoid), and hormonal/life-cycle status—may account for the differing directionality and magnitude observed between sexes.
Although gender differences in heart rate variability have been extensively examined in the literature, the contribution of this study lies in its application to a specific occupational population characterized by high exposure to chronic stress—teachers—and in the integration of autonomic and metabolic indicators through a direct measure of adiposity [25]. In this context, the results reveal sex-differentiated patterns in the relationship between body fat percentage and autonomic modulation, with more linear associations in male teachers and more heterogeneous responses in females [14]. These physiological profiles are particularly relevant from an occupational health perspective, as teaching is consistently associated with trajectories of mental overload, professional burnout, and declining well-being [26,27]. The HRV alterations observed in relation to adiposity may represent an underlying physiological mechanism linking chronic work-related stress with cardiometabolic risk and burnout [25]. Within this framework, HRV emerges as a potentially useful biomarker for identifying vulnerability profiles and guiding tailored preventive interventions in educational settings [28].
In relation to these findings, although the women in the sample exhibited a higher average body fat percentage, their HRV profiles did not show a parallel and consistent reduction in vagal indices, as was observed in men. This finding is consistent with evidence indicating higher baseline vagal activity at rest and a distinct autonomic organization in women, even under stress or elevated adiposity [8,24]. The absence of linear associations does not imply a lack of effect but rather a more complex regulation, potentially modulated by respiratory, hormonal, and adipose tissue distribution factors.
Complementarily, in men, the relationship between adiposity and heart rate variability showed a pattern consistent with sustained sympathetic activation and progressive parasympathetic withdrawal. This imbalance was reflected in significant reductions in RMSSD and pNN50 (−26.46% and −42.15% in the group with higher body fat percentage), along with lower SD1 and SD2 values, suggesting reduced regulatory capacity in response to stressors and diminished physiological flexibility [29,30]. These findings have been consistently associated with increased cardiometabolic risk [31]. The consistency of this relationship may be explained by a predominantly central and visceral fat distribution—typical of the male phenotype—closely linked to low-grade inflammation, insulin resistance, and chronic sympathetic hyperactivation, mechanisms that contribute to cardiac autonomic dysfunction and a sustained reduction in vagal modulation [32,33].
To explain the lower linearity observed in women, it is essential to consider the physiological meaning of HRV domains. The female results show an apparent decoupling between the time domain (RMSSD/pNN50) and the frequency domain (LF, HF, and LF/HF). It is important to recall that LF/HF is not a “pure sympathetic” index: the LF component primarily reflects cardiovagal baroreflex modulation rather than direct cardiac sympathetic innervation, meaning that variations in LF/HF may arise from changes in baroreflex gain rather than shifts in sympathetic tone [34,35]. Moreover, HF is strongly influenced by respiratory sinus arrhythmia (RSA); changes in respiratory rate and depth can modify HF without parallel changes in RMSSD/pNN50. Breathing within 0.15–0.40 Hz (≈9–24 breaths/min) amplifies HF, whereas if respiratory frequency falls below 0.15 Hz, a portion of respiration-related variability migrates to LF, thereby altering LF/HF without reflecting true changes in basal autonomic tone [36]. In obesity, mechanical respiratory alterations (increased ventilatory workload, shallower breathing patterns, and changes in lung volumes) modulate RSA and, consequently, frequency-domain indices [37,38]. Taken together, elevated HF combined with reduced LF and a low LF/HF ratio in women with higher body fat percentage suggests simultaneously greater high-frequency respiratory-vagal coupling and reduced baroreflex modulation, which helps contextualize the reduced linearity observed.
These observations are consistent with the heterogeneity described in the literature and highlight the role of fat distribution. Available evidence suggests that the relationship between obesity and HRV is not uniform and, in some cases, disappears when comorbidities are controlled for: in healthy adults aged 30–60 years, no differences in classic HRV indices were observed between individuals with and without obesity [39]. In contrast, fat distribution—rather than overall BMI—appears to be key: central adiposity (waist circumference, WHR) is associated with lower parasympathetic activity (reduced HF, RMSSD, and pNN50) and higher LF/HF, whereas body mass index (BMI) may not correlate with HRV markers [29]. In adolescents, waist circumference more accurately discriminates autonomic dysfunction than general adiposity, with negative correlations of RMSSD and pNN50 after adjusting for age, sex, and cardiorespiratory fitness [40]. This heterogeneity is better understood when considering obesity phenotypes (e.g., MHO/MUO), which differ in inflammation, adipokines, insulin resistance, and fat distribution, all of which modulate HRV in different ways [41,42]. Moreover, android adiposity is linked to higher cardiometabolic risk, whereas gynoid adiposity shows distinct associations; in the general population, a higher android/gynoid ratio is associated with NAFLD and fibrotic NASH and shows clear sex-related differences [43].
From a methodological perspective, the lack of significance in RMSSD and pNN50 in women warrants careful consideration. Although both are robust vagal indices, they are less sensitive to subtle respiratory variations, show high intra-subject variability, and are mathematically dependent on heart rate. Even minimal changes in heart rate can substantially affect HRV and its reproducibility. Therefore, an increased HF together with non-significant RMSSD/pNN50 values may be compatible with predominant respiratory–vagal coupling in the frequency domain, without sufficient changes in the time domain after adjusting for heart rate [44,45].
Additional physiological factors may also modulate the relationship between body fat percentage and HRV. Women often exhibit higher levels of stress and neuroticism-related traits, which favor greater sympathetic activation, particularly in the context of elevated adiposity [13,46]. Chronic stress may disrupt autonomic regulation and promote anabolic processes such as lipogenesis, with central effects [47]. In turn, excess fat—especially abdominal fat—is associated with chronic sympathetic hyperactivity, which can distort the interpretation of HRV parameters [48], thereby contributing to the variability of results in women [32]. Overall, higher daily stress is associated with lower HRV, RMSSD, and pNN50, with more pronounced effects in the presence of obesity or other metabolic and psychophysiological dysfunctions [49].
In the teaching profession, this interaction becomes particularly relevant. HRV tends to decline throughout the academic year in parallel with mental exhaustion, accompanied by elevated morning cortisol and signs of work overload [22]. In this context, women may maintain relatively higher vagal modulation at rest—reflected in higher RMSSD and pNN50 values—suggesting a more robust parasympathetic response even under stress [24].
Recent ambulatory evidence in teachers shows reduced HRV during teaching days compared to rest days, as well as anticipatory stress before classes begin and insufficient midday recovery. Furthermore, student aggression and a high proportion of frontal teaching are associated with lower HRV, whereas more positive teacher–student relationships correlate with higher HRV. These findings situate our observations within a continuum of psychosocial demands inherent to the real classroom environment and reinforce the need for interventions aimed at improving classroom climate and creating recovery opportunities during the working day [16].
Additionally, hormonal factors and life-cycle stages substantially influence the relationship between body fat percentage and HRV. The menopausal transition and fat distribution—particularly visceral versus subcutaneous accumulation—significantly modulate HRV and account for part of the variability observed across studies and life stages [13,50]. Postmenopausal women more frequently exhibit increases in visceral fat along with associated HRV alterations [51]. Consistent with meta-analytic evidence, women at rest generally show higher HF, lower LF, and a lower LF/HF ratio than men, with these effects being modulated by age and by respiratory control during recording [14,24].
In summary, the relationship between adiposity, stress, and HRV in women is mediated by multiple regulatory systems and does not follow a linear progression. This greater physiological complexity may confer autonomic resilience during certain life-cycle stages, but it also complicates the detection of clear associations when variables such as respiration, baroreflex sensitivity, or hormonal status are not controlled. In men, by contrast, the association is more linear and accompanied by sustained vagal withdrawal and increased cardiometabolic risk.
These findings are consistent with previous literature, although it is important to note that most studies use body mass index as a marker of obesity rather than direct measures of adiposity. In this regard, the work by Yadav et al. [29] reported consistent associations between obesity and autonomic dysfunction, with significant reductions in RMSSD and pNN50 and an increase in the LF/HF ratio in the obese group. The reduction in RMSSD described in that study (−22.97%) is comparable to that observed in our male sample, which reinforces the validity of our results, although discrepancies in LF/HF highlight the influence of adiposity classification methods and of modulating factors such as respiration.
Consistently, a large population-based study (8538 adults) reported stronger associations between obesity—both general and abdominal—and HRV in men than in women, supporting the sex-specific pattern observed in our sample [52]. This sex difference has been widely confirmed by meta-analyses showing higher baseline HRV values in women than in men, even after adjusting for age and other confounders [24]. Overall, the literature reveals a more consistent relationship between adiposity and autonomic modulation in men, whereas results in women are less predictable.
In our study, this heterogeneity was particularly evident in the group with the highest body fat percentage, where women exhibited relatively higher HRV values than men. This profile may help explain the apparent inconsistencies described in the PG%–HRV relationship in female populations. Nonetheless, several studies have indicated that when adiposity is elevated, women may also show reductions in time-domain vagal indices such as RMSSD and pNN50, in line with our findings [13,46]. The clinical relevance of this phenomenon lies in the fact that sustained parasympathetic withdrawal or sympathetic overactivation is associated with increased cardiovascular and metabolic mortality [53]. It has been proposed that sex differences in vagal activity and sympathovagal balance significantly influence cardiovascular health and may explain the higher risk associated with excess adiposity in men compared to women [54].
Moreover, our study identified an association between higher body fat percentage and older age in teachers. Aging is accompanied by a reduction in basal metabolic rate and by hormonal and metabolic alterations, such as insulin resistance, that promote the accumulation of body fat [55]. In the teaching profession, this process appears to be intensified by chronic stress and high workload, placing this group among those with the lowest psychological well-being [56]. These factors may exacerbate metabolic and hormonal imbalances that favor fat accumulation, particularly in visceral and ectopic depots [57].
The prevalence of overweight observed in our sample (35.90% according to BMI) is similar to that reported in the Spanish adult population (37.10%), suggesting that teachers do not constitute an exception in terms of excess body weight [55]. Moreover, more than half of the participants exhibited elevated adiposity levels (53.60%), in line with studies conducted in active Spanish workers of similar ages [56], further reinforcing the epidemiological representativeness of the sample analyzed.
Our study also revealed a relationship between greater work experience and higher body fat percentage. One possible explanation is the progressive increase in responsibilities and workload over the course of a teaching career, which may promote sustained stress and dysregulation of the HPA axis. These processes are associated with insulin resistance and metabolic alterations that foster adipogenesis [58]. In this regard, a longitudinal study in U.S. teachers found that each additional year of work experience increased the likelihood of being overweight or obese by 2.2% [59].
Finally, teachers who reported higher levels of perceived stress predominantly belonged to the group with the highest body fat percentage. Self-reported chronic occupational stress has been identified as an independent risk factor for obesity [60], with significant increases in the risk of elevated—particularly abdominal—adiposity among individuals with high perceived stress levels [61]. This finding reinforces the importance of simultaneously considering psychosocial and physiological factors when examining adiposity and autonomic regulation in the teaching population.

3.1. Limitations and Future Research Directions

This study has several limitations that should be acknowledged. First, the cross-sectional design limits the ability to infer causal relationships between autonomic nervous system function and body fat percentage. Longitudinal and, where appropriate, experimental studies are required to clarify the directionality of these associations and the underlying physiological mechanisms.
Second, although the sample size was adequate for exploratory purposes, it limits the generalizability of the findings. Future studies should include larger and more diverse samples, both geographically and occupationally, to validate these results. Additionally, body composition was assessed using bioelectrical impedance analysis (BIA), which, although practical and widely used, has lower precision than reference methods such as dual-energy X-ray absorptiometry (DXA). Therefore, it is recommended that more accurate techniques be incorporated to quantify body fat and its regional distribution
An additional limitation is the absence of respiratory monitoring and control during HRV acquisition, which may influence the HF band and, under certain conditions (such as slow breathing), shift spectral content toward LF, thereby affecting the interpretation of the LF/HF ratio. Likewise, baroreflex sensitivity was not assessed, despite the fact that the LF component primarily reflects baroreflex-mediated modulation, which limits the physiological interpretation of the frequency domain. Future research should incorporate respiratory monitoring and baroreflex quantification to strengthen the interpretation of HRV frequency-domain parameters [34,35,36]. Although the LF/HF ratio is presented in the adjusted results—where, in women, it showed a statistically significant difference of small magnitude—its interpretation should remain cautious given its sensitivity to ventilatory patterns and baroreflex gain, as well as the absence of respiratory and baroreflex sensitivity recordings in our design. Likewise, no formal correction for multiple comparisons was applied across the different HRV indices and sex strata; therefore, significant findings with small effect sizes (e.g., HRmax and LF/HF in women) should be interpreted cautiously and require confirmation in independent samples and protocols that include respiratory control.
Finally, the study focused on teachers from institutions within the Community of Madrid, which may limit the generalizability of the results to other regions and professional groups. Expanding research to different geographic areas and occupational sectors would provide a more comprehensive understanding of the role of work-related stress and adiposity in autonomic modulation.
Although the analyses were adjusted for age, teaching experience, and educational level, no individual information was available regarding caffeine or tobacco consumption, nor about menstrual cycle phase or hormonal status in women; accordingly, these variables could not be included as covariates in the adjusted models. Therefore, residual confounding arising from these factors cannot be ruled out, nor can potential differences in workload, academic calendar, and non-teaching duties, which may vary across educational levels. In addition, the %BF × educational level interaction was not evaluated due to insufficient statistical power and should therefore be examined in future studies.
Additionally, dichotomizing fat mass using the sex-specific median (≥p50 vs. <p50) may entail a loss of information and statistical power compared with continuous models. Although we applied ANCOVA adjusted for age, teaching experience, and educational level to mitigate confounding, future studies should compare these findings using the predictor in its continuous form and incorporating regional adiposity measures (e.g., central vs. peripheral distribution).

3.2. Practical Applications

The findings of this study have important practical implications for occupational health and stress-management programs. Specifically, the observed association between higher body fat percentage, elevated perceived stress levels, and reduced heart rate variability—particularly pronounced in male teachers—provides an empirical basis for designing more targeted preventive interventions within educational settings. The relationship between increased body fat percentage and decreased HRV, especially among male teachers, underscores the need for tailored strategies aimed at stress management and cardiovascular health promotion in this population. This becomes even more relevant when considering the real psychosocial demands of the classroom and the insufficient recovery patterns observed during the teaching workday.
Educational institutions could implement wellness programs that include regular physical activity, stress-reduction techniques such as mindfulness and relaxation exercises, as well as nutritional counseling, with the aim of addressing both the psychological and physical health of teachers. In this context, recent evidence in teaching populations particularly supports the implementation of structured meditation and mindfulness programs—such as Mindfulness-Based Stress Reduction (MBSR) and brief or self-guided modalities—which have demonstrated significant reductions in perceived stress and improvements in psychological well-being and emotional self-regulation. In male teachers specifically, the findings of this study suggest that interventions aimed at reducing adiposity and enhancing parasympathetic modulation—such as structured aerobic exercise programs and targeted strategies for managing occupational stress—may be especially relevant for reducing cardiometabolic risk, particularly when combined with autonomic regulation techniques applied before or after periods of high teaching demand.
In the case of female teachers, in whom the relationship between adiposity and heart rate variability was more heterogeneous and dependent on the analytical domain, intervention programs may benefit from a more integrative approach that considers not only body composition but also physiological modulating factors such as hormonal status, respiratory patterns, and the balance between work demands and recovery periods. In this regard, interventions based on mindfulness, meditation, and guided breathing techniques may enhance autonomic recovery and improve resilience to stress, in line with the variability observed in time- and frequency-domain HRV indices in women.
Furthermore, the results support the use of heart rate variability as an objective, non-invasive, and easily applicable tool for monitoring stress and autonomic regulation in teachers. The incorporation of periodic HRV measurements would not only allow for the identification of individuals with greater vulnerability but also facilitate the evaluation of the effectiveness of specific interventions—such as mindfulness programs, recovery breaks during the working day, and improvements in classroom climate—and enable the adjustment of preventive strategies in a personalized manner according to sex and adiposity level. By prioritizing teachers’ mental and physical health, educational institutions can enhance job satisfaction, reduce professional burnout, and increase overall productivity.
Based on the available evidence in teachers, we propose a stepped intervention package. First, we recommend mindfulness or meditation programs such as Mindfulness-Based Stress Reduction (MBSR), delivered over eight weeks, which have demonstrated reductions in perceived stress and improvements in teaching self-efficacy and classroom climate [62]. Second, we suggest brief or self-guided online formats, which are well suited to teachers’ workloads and have shown positive effects on well-being and mindfulness skills [63]. Third, we propose guided breathing and cardiac coherence practices (≈6 breaths/min) as micro-interventions lasting 8–10 min before or after lessons, which can acutely increase RMSSD [64]. Fourth, we consider organizational strategies aimed at improving classroom climate and creating midday recovery windows to be valuable, as they promote more stable autonomic regulation among teachers [65]. Taken together, these strategies provide a practical, evidence-based framework for reducing teacher stress and enhancing their psychophysiological well-being.

4. Materials and Methods

4.1. Design, Setting, and Participants

A cross-sectional observational study was conducted with 253 teachers (27.3% men; 72.7% women) from compulsory and university education in the Community of Madrid during the 2022–2023 academic year. Recruitment was carried out through institutional channels (distribution lists and staff-meeting announcements), with voluntary participation and informed consent obtained after providing detailed information about the study objectives, procedures, and ethical considerations. After data collection, all information was anonymized and any identifying elements were removed. The study received approval from the Ethics Committee (CIPI/213006.55) and adhered to the Declaration of Helsinki [66]. Exclusion criteria included diagnosed cardiovascular disease, chronic psychiatric disorders, or medication affecting heart rate (e.g., beta-blockers). Participation was entirely voluntary, and teachers could withdraw at any time without consequences.
Sample size was determined through a power analysis (target: detect a medium effect size, d = 0.50; power = 0.80; α = 0.05). Although the minimum estimated sample was 200 participants, a larger cohort was recruited to compensate for potential dropouts and to increase the robustness of the study.

4.2. Instruments

4.2.1. Heart Rate Variability (HRV)

Standard procedures commonly used in previous research were employed [67,68]. Cardiac autonomic modulation was assessed through HRV by recording R–R intervals (intervals between consecutive normal beats) using a Polar V800 monitor (Polar, Kempele, Finland). The operational details of the recording procedure are described in the Procedure section.
Signal processing was performed using Kubios HRV (specific software for heart rate variability analysis, version 4.1), applying automatic artifact detection and correction and establishing a quality criterion of <5% corrections for inclusion in the analysis.
Time-domain and non-linear indices were selected—RMSSD (root mean square of successive differences), pNN50 (percentage of adjacent R–R intervals differing by >50 ms), and SD1/SD2 (short- and long-term dispersion of the Poincaré plot)—along with frequency-domain parameters—LF (low frequency band), HF (high frequency band), and the LF/HF ratio—following current recommendations to capture short-term vagal components and spectral variability [69].
As discussed in the manuscript, interpretation of LF/HF was approached with caution due to its sensitivity to respiration and baroreflex activity, in line with current methodological guidelines. Therefore, greater emphasis was placed on time-domain vagal indices (e.g., RMSSD) for the main comparisons.

4.2.2. Body Composition

Body composition was assessed using bioelectrical impedance analysis (BIA) with the InBody 720 device, following the manufacturer’s standardized protocol. Estimation focused on adipose tissue mass (ATM), considered a primary indicator of obesity [68]. For clinical classification, international Siri reference values were used, and for comparative analyses, a sex-specific median split (<p50 vs. ≥p50) was applied to account for sexual dimorphism in body composition [23].

4.2.3. Psychometric Measures (If Included in Methods)

Perceived stress was assessed using a 0–10 Likert-type scale (0 = no stress; 10 = maximum stress). This measure is a pragmatic indicator and does not correspond to a standardized or validated questionnaire specifically designed for occupational stress; therefore, its results should be interpreted with caution.

4.3. Procedures

Assessments were conducted at the beginning of the academic year in a single session per participant and during working hours, to minimize potential effects of accumulated fatigue. Each recording was carried out individually in a room specifically prepared for the study, with controlled noise, temperature, and external distractions.
Teachers were instructed to maintain spontaneous breathing and their usual morning routine (e.g., breakfast), avoiding any respiratory control exercises or biofeedback practices before or during the measurement. During the HRV recording, participants remained seated at rest (~6 min), refraining from voluntary maneuvers that could alter heart rate or ventilatory patterns.
The appointment schedule was organized according to the teachers’ availability over three days at each school, ensuring minimal interference with their teaching duties. The recording protocol was identical for men and women, maintaining homogeneous conditions across all sessions.

4.4. Statistical Procedures

Data are presented as mean ± standard deviation (SD). The normality of quantitative variables was assessed using the Kolmogorov–Smirnov test, complemented by histogram and Q–Q plot inspection, and homoscedasticity was verified using Levene’s test.
The sample was divided into two adiposity groups according to the sex-specific median of body fat mass (kilograms), considering sexual dimorphism in body composition. Group 1 included participants with body fat mass equal to or below the sex-specific 50th percentile (<p50), classified as having adequate adiposity, whereas Group 2 comprised those with values above this median (≥p50), classified as having a high level of adiposity.
Variables showing a normal distribution were compared using the independent-samples Student’s t-test, whereas those not meeting the assumption of normality were analyzed using the non-parametric Mann–Whitney U test. Proportions were compared using the χ2 test, applying Fisher’s exact test when any expected frequency was <5.
Educational level was recorded and considered a potential confounding factor. For this reason, comparisons involving this variable are not presented in this section but reported in the Results. In multivariable analyses (ANCOVA and linear regression), educational level was included as a covariate along with age and teaching experience, while all analyses were stratified by sex. The potential interaction between body fat percentage and educational level was not assessed due to insufficient statistical power.
ANCOVA analyses were performed to compare participants according to adiposity group (<p50 vs. ≥p50), defined using the sex-specific median of fat mass (kg) calculated from valid records. Models were adjusted for age (years), teaching experience (years), and educational level. For each dependent variable (MeanHR, HRmin, HRmax, RMSSD, pNN50, LF, HF, LF/HF, SD1, and SD2), partial eta squared (ηp2) was reported as the index of adjusted effect size (small ≈ 0.01; moderate ≈ 0.06; large ≈ 0.14).
To provide information on the practical magnitude of the observed differences, effect sizes were calculated for all main comparisons: Cohen’s d for parametric contrasts (small = 0.20; moderate = 0.50; large = 0.80) and the r coefficient for non-parametric contrasts.
Additionally, linear regression models were estimated, also stratified by sex, using HRV parameters as dependent variables and body fat percentage as the continuous predictor, adjusting for age, teaching experience, and educational level. When necessary, the assumptions of linearity and homoscedasticity were verified through residual analysis.
Individual information on caffeine or tobacco consumption, or on menstrual cycle phase or hormonal status in women, was not available; therefore, these variables could not be included as covariates in the adjusted models.
The selection of HRV indices and the quality control of the recordings followed current methodological recommendations in educational research, including the combined use of time- and frequency-domain indices, an adequate recording duration, and the review/correction of artifacts prior to analysis.
The level of statistical significance was set at p ≤ 0.05. All analyses were performed using IBM SPSS Statistics v29 (IBM Corp., Armonk, NY, USA).

5. Conclusions

This study contributes to the understanding of gender differences in autonomic regulation by jointly analyzing heart rate variability and body fat percentage in teachers. The findings show that higher adiposity is associated with higher levels of perceived stress and lower heart rate variability, particularly in men, suggesting a more pronounced autonomic dysregulation profile in this group.
Relevant sex-related differences were observed in the magnitude and pattern of these associations. While in men the relationship between greater adiposity and reduced vagal indices was more consistent at the descriptive level but did not reach significance after adjustment for any variable (null–small effects), in women HRmax and the LF/HF ratio were significant after adjustment (small effects), whereas RMSSD, pNN50, LF, HF, SD1, and SD2 did not reach significance (with slight trends for LF and HF). This profile is compatible with a frequency-domain pattern of LF↓/HF↑/LF/HF↓ in the ≥p50 group of small magnitude, statistically consistent only for LF/HF; however, it should be interpreted with caution given the sensitivity of LF/HF to respiration and baroreflex activity and the absence of respiratory recording in our design. These findings underscore the need for sex-specific approaches in both research and occupational health interventions.
Given the cross-sectional design of the study, the results do not allow causal relationships to be established or the directionality between stress, adiposity, and autonomic regulation to be determined. Nevertheless, the observed associations are consistent with previous theoretical models proposing a bidirectional interaction between chronic stress, autonomic nervous system dysfunction, and body adiposity. Future longitudinal and experimental studies will be required to clarify the temporal and causal mechanisms underlying this relationship.

Author Contributions

Conceptualization, P.B.-d. and V.J.C.-S.; Methodology, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; software, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; validation, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; formal analysis, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; investigation, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; resources, A.C.G., P.B.-d. and V.J.C.-S.; data curation, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; writing—original draft preparation, E.Á.-G., A.C.G. and M.I.R.-G.; writing—review and editing, M.I.R.-G., P.B.-d. and V.J.C.-S.; visualization, E.Á.-G., A.C.G., P.B.-d. and V.J.C.-S.; supervision, P.B.-d. and V.J.C.-S.; project administration, P.B.-d. and V.J.C.-S.; funding acquisition, P.B.-d. and V.J.C.-S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki, and approved by University Bioethics Committee (CIPI/213006.55).

Data Availability Statement

The datasets generated during and/or analysed in the current study are available from the corresponding author upon reasonable request.

Acknowledgments

We would like to express our gratitude to all the schools in the Community of Madrid that kindly agreed to participate in the project. We appreciate their willingness and extend a warm thank you to Montessori School, Nicoli School, Berriz School, Joyfe School, Aquila School, and Helicon School. Additionally, we would like to thank Universidad Europea for providing the opportunity to collect data from university lecturers. Finally, we acknowledge the significant contributions of the professors who participated and collaborated in the study.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Key Influences on Competitive Load in Youth Regional Teams During National Basketball Competition
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