The transition from adolescence to adulthood is a critical period marked by lifestyle choices that have long-term health implications. Among these, physical activity plays a pivotal role in determining body composition and metabolic efficiency. Sedentary behavior, characterized by low energy expenditure activities such as prolonged sitting or screen time, has become increasingly prevalent among young adults, especially in urban and academic settings (1,2). This trend is associated with increased adiposity, reduced lean muscle mass, and impaired metabolic function, all of which contribute to the early onset of lifestyle-related disorders such as obesity, insulin resistance, and cardiovascular disease (3,4).

Body composition refers to the proportion of fat mass and fat-free mass in the body and serves as an important indicator of metabolic health. Physically active individuals tend to maintain a healthier ratio of lean to fat mass, which positively influences basal metabolic rate (BMR), insulin sensitivity, and lipid profiles (5,6). Conversely, a sedentary lifestyle is often linked to an increase in fat mass and a reduction in metabolic rate, even in individuals with a normal body mass index (BMI), underscoring the limitation of BMI as a sole indicator of health (7).

Resting metabolic rate (RMR), which represents the energy expenditure of the body at rest, is influenced by several factors including muscle mass, age, sex, and physical activity levels (8). Regular exercise, particularly resistance and aerobic training, has been shown to enhance RMR by increasing muscle mass, thereby contributing to greater daily energy expenditure and improved weight regulation (9,10).

Although several studies have examined the effects of physical activity on metabolic parameters in adults, there is a relative paucity of data focusing specifically on young adults during their college years—a stage when sedentary behaviors tend to increase, and exercise adherence declines (11). Moreover, direct comparative studies analyzing both body composition and metabolic rate in sedentary versus physically active young adults are limited.

Therefore, this study aims to compare body composition indices and resting metabolic rate between sedentary and physically active young adults. The findings are intended to underscore the metabolic benefits of maintaining regular physical activity during early adulthood and provide evidence for targeted interventions promoting active lifestyles in this age group.

Study Design and Participants

This was a cross-sectional observational study conducted over a period of three months. A total of 80 young adults aged between 18 and 25 years were enrolled using convenience sampling. Participants were recruited from university students through campus announcements and online registration forms. They were divided equally into two groups based on their physical activity levels: sedentary group (n = 40) and physically active group (n = 40).

Inclusion and Exclusion Criteria

Inclusion criteria included healthy individuals within the specified age range, with no known history of metabolic, endocrine, or cardiovascular diseases. Participants were excluded if they were on any medication that could affect metabolism, had a history of chronic illness, or were actively engaged in competitive sports training (for the sedentary group).

Assessment of Physical Activity Level

Physical activity status was assessed using the International Physical Activity Questionnaire – Short Form (IPAQ-SF). Individuals reporting less than 600 MET-min/week of total activity were classified as sedentary, while those meeting or exceeding 1500 MET-min/week of vigorous or combined moderate-vigorous activity were categorized as physically active.

Anthropometric and Body Composition Measurements

Height was measured to the nearest 0.1 cm using a stadiometer, and body weight was recorded using a calibrated digital scale. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/m²). Body composition analysis, including fat mass (%), fat-free mass (kg), and total body water (%), was performed using a bioelectrical impedance analysis (BIA) device (Tanita MC-780U, Japan), with standard positioning and pre-assessment guidelines (e.g., no food or exercise 2 hours prior).

Measurement of Resting Metabolic Rate

Resting metabolic rate (RMR) was measured using indirect calorimetry with a portable metabolic analyzer (Fitmate GS, COSMED, Italy). Participants were instructed to avoid food, caffeine, and strenuous activity for at least 12 hours before the test. RMR measurements were taken in a quiet, thermoneutral environment with participants lying supine, relaxed, and awake for at least 20 minutes.

Statistical Analysis

All data were entered into Microsoft Excel and analyzed using SPSS version 25.0 (IBM Corp., USA). Descriptive statistics were used to summarize demographic and clinical characteristics. Independent t-tests were employed to compare continuous variables between the two groups. A p-value of less than 0.05 was considered statistically significant.

A total of 80 participants (40 sedentary and 40 physically active) were included in the study. The mean age of the sedentary group was 21.8 ± 1.9 years, and the physically active group was 22.1 ± 2.0 years, with no statistically significant difference in age distribution (p = 0.47).

Anthropometric and Body Composition Parameters

Table 1 shows the comparison of body composition parameters between the two groups. The sedentary group had a higher mean body fat percentage (26.4% ± 3.9) compared to the physically active group (19.2% ± 4.2), which was statistically significant (p < 0.001). Additionally, lean body mass was significantly higher in the active group (55.6 ± 5.4 kg) versus the sedentary group (48.9 ± 6.2 kg) (p = 0.002). No significant difference was found in BMI between the groups (p = 0.28) (Table 1).

Table 1. Comparison of Body Composition Parameters between Sedentary and Active Groups

*Statistically significant difference

Resting Metabolic Rate and Energy Expenditure

As shown in Table 2, the resting metabolic rate (RMR) was significantly higher in the physically active group (1612 ± 132 kcal/day) than in the sedentary group (1456 ± 126 kcal/day) (p = 0.001). Total daily energy expenditure (TDEE), estimated through BIA and adjusted for activity level, also showed a marked difference between groups (p < 0.001) (Table 2).

Table 2. Comparison of Metabolic Parameters

*Statistically significant difference

Correlation between Lean Mass and Metabolic Rate

A Pearson correlation analysis revealed a strong positive correlation between lean body mass and resting metabolic rate (r = 0.76, p < 0.001), indicating that individuals with higher lean mass tend to have elevated metabolic rates (Table 3).

Table 3. Correlation between Lean Body Mass and Resting Metabolic Rate

*Statistically significant

This study demonstrated that physically active young adults had significantly lower body fat percentage, higher lean body mass, and elevated resting metabolic rate (RMR) compared to their sedentary counterparts. These findings align with previous research emphasizing the beneficial role of regular physical activity in modulating body composition and metabolic health during early adulthood (1,2).

The lower fat percentage observed in the active group can be attributed to enhanced lipolytic activity and increased caloric expenditure through both exercise-induced and post-exercise oxygen consumption (3,4). Physical activity, particularly resistance and aerobic training, has been shown to reduce adiposity by increasing mitochondrial density and fat oxidation capacity in skeletal muscle (5). The active participants in our study also exhibited significantly greater lean mass, a factor known to contribute directly to higher RMR due to the greater energy demands of metabolically active tissues (6,7).

Interestingly, despite no significant difference in body mass index (BMI) between the groups, the differences in fat and lean mass underscore the limitations of BMI as an indicator of metabolic health. Similar conclusions were drawn in earlier reports, which noted that individuals with normal BMI but higher body fat levels still possess elevated metabolic risk (8,9). This highlights the importance of direct body composition assessment in young adults, rather than reliance solely on BMI.

The observed increase in RMR among active individuals is consistent with the understanding that muscle tissue has a higher resting energy requirement than adipose tissue (10). Studies have shown that even modest gains in lean mass can translate to meaningful increases in daily caloric expenditure, potentially aiding in long-term weight maintenance and metabolic resilience (11,12). Additionally, our correlation analysis confirmed a strong positive association between lean mass and RMR, further supporting this physiological relationship.

The implications of these findings are particularly relevant considering the rising trend of sedentary lifestyles among young adults, especially university students. Academic workload, screen-based activities, and lack of structured physical education contribute to reduced energy expenditure and unfavorable changes in body composition (13). Encouraging structured physical activity interventions, such as campus-based fitness programs, may be an effective strategy to counteract these trends.

Several limitations of this study should be acknowledged. First, the cross-sectional design limits causal inferences. Longitudinal studies are needed to establish temporal relationships between physical activity patterns and metabolic changes. Second, physical activity levels were self-reported via questionnaire, which may introduce recall bias. However, the IPAQ-SF has been validated in multiple populations and remains a widely accepted tool for large-scale physical activity assessment (14).

Despite these limitations, the study provides important insights into how lifestyle behaviors impact metabolic health even in young, ostensibly healthy individuals. Early adulthood represents a critical window for establishing habits that influence long-term health trajectories. Interventions targeting improved body composition and metabolic efficiency at this stage could contribute to the prevention of obesity, metabolic syndrome, and related non-communicable diseases later in life (15).

This study highlights the significant impact of regular physical activity on body composition and metabolic rate in young adults. Physically active individuals exhibited lower body fat, higher lean mass, and increased resting metabolic rate compared to their sedentary counterparts. These findings underscore the importance of promoting active lifestyles during early adulthood to enhance metabolic health and prevent future lifestyle-related diseases.

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