Sedentary behavior–characterized by waking behaviors in a sitting, reclining, or lying posture and energy expenditure ≤1.5 metabolic equivalents (METs) (Tremblay et al., 2017) – has been associated with several adverse health outcomes including obesity, metabolic syndrome, type 2 diabetes (T2D), cardiovascular diseases, and mortality, independently of physical activity levels (Davi et al., 2018; Patterson et al., 2018; Ekelund et al., 2019). A growing body of evidence has also suggested that prolonged sedentary behavior may negatively impact health-related quality of life (HRQoL) (Kim et al., 2017; Kolt et al., 2017), capacity to cope with stress (Gilson et al., 2017; Gubelmann et al., 2018) and sleep quality (Koohsari et al., 2023; Liangruenrom et al., 2023). These domains have been increasingly acknowledged as important health outcome measures.

HRQoL is a multidimensional concept encompassing physical, emotional, mental, and social wellbeing (Collins et al., 2021). Reduced HRQoL has been associated with worse clinical outcomes, such as hospitalization and premature mortality (Phyo et al., 2020). Psychological stress is a negative emotional state that may cause a variety of negative conditions, including poor mental health (O’Connor et al., 2021), increased risk of anxiety and depression disorders (Wiegner et al., 2015), sleep problems (Chen et al., 2023), cardiovascular diseases (Sara et al., 2018), metabolic syndrome and type 2 diabetes (T2D) (Harris et al., 2017), and premature death (Prior et al., 2016). Due to their convenient collection and analysis, salivary biomarkers are easily included in neuroendocrine (stress) research (Strahler et al., 2016). Among these, salivary cortisol has been routinely used as a biomarker of psychological stress and related physical and mental conditions (Hellhammer et al., 2009). It is considered a reliable measure of the hypothalamic-pituitary adrenal axis (HPA) adaptation to stress (Hellhammer et al., 2009). In addition, salivary alpha-amylase activity has been recognized as a reliable and rapid biomarker for measuring response to stress across different clinical settings, including those in psychology and neuroscience (Aita et al., 2024). This enzyme is recognized as a valid and reliable marker of autonomic nervous system (ANS) (dys)function in stress-related research (Strahler et al., 2016; Ali and Nater, 2020). Importantly, the European Agency for Safety and Health at Work found that 59% of Portuguese workers indicate that stressful situations are common in their workplaces (European Agency for Health and Safety at Work, 2013).

Most working adults spend approximately 8 h a day at work, so occupational tasks and work settings may significantly impact their movement behaviors (Prince et al., 2019). A review found that working adults spent about 60% of their working and waking time sedentary, and only 4% of the day included physical activity of moderate-to-vigorous intensity (Prince et al., 2019). Furthermore, the desk-based workers revealed the greatest time in sedentary behaviors and the lowest time in physical activity (Prince et al., 2019). The authors suggested that effective interventions that promote health-enhancing physical activity are needed to mitigate the harmful impact of sedentary behavior among workers (Prince et al., 2019).

Regular exercise has been recognized as a promising non-pharmacological strategy for preventing and treating many health issues (Pedersen and Saltin, 2015). Studies showed that physically active adults were more likely to report better HRQoL (DiPietro et al., 2019), satisfaction with life (Zayed et al., 2018), and increased capacity to deal with stress (Gubelmann et al., 2018; Scully et al., 1998) compared to their sedentary peers. Current evidence from clinical trials indicates that participation in an exercise program may have a beneficial effect on HRQoL domains (Collins et al., 2021; Pietta-Dias et al., 2019). In turn, the evidence about the impact of an exercise program on perceived stress is poorly studied, evidencing either conflicting or null exercise effects (Carraça et al., 2021). Among the different exercise modes, the World Health Organization (WHO) recommends that adults accumulate an average weekly volume of 150–300 min of moderate-intensity or 75–150 min of vigorous-intensity and two or more days a week of muscle-strengthening activities at moderate or greater intensity for greatest health improvements (Bull et al., 2020). This is consistent with a previous study conducted on healthy older adults that found that combined aerobic and resistance training resulted in higher amelioration in quality of life compared to aerobic or resistance training alone (Pietta-Dias et al., 2019). Similarly, Collins et al. (2021) also found that 8 months of combined exercise training had the greatest improvement in physical component score, mental component score, and individual subdomain scores of HRQoL compared with aerobic or resistance training alone. However, conflicting results were found in other studies. Tozetto et al. (2022) found that a fixed intensity combined training was effective in improving the mental component score but not the physical component in adults with obesity. Similarly, Sillanpää et al. (2012) found an improvement in general health (subdomain of physical component) and a tendency to worsen the domains of role-physical and bodily pain in sedentary middle-aged and older adults. The experimental studies assessing salivary alpha-amylase and cortisol measurements in the context of exercise training are still scarce and present inconsistent results. A study (Klaperski et al., 2014) investigated the impact of a 12-week exercise training program on physiological stress response to a psychosocial stressor and found that exercise training significantly improved fitness and reduced stress reactivity, measured by cortisol, heart rate, and heart rate variability. In turn, a study in institutionalized older women (Rieping et al., 2019) found that 14 weeks of chair-based aerobic training and chair-based elastic-band strength training promoted a slight (but non-significant) increase in alpha-amylase and cortisol levels.

Evidence about the effects of combined aerobic and resistance training on HRQoL domains and stress is insufficient and controversial in literature. Therefore, this study aimed to evaluate the effects of 16 weeks of combined training on the HRQoL and stress levels (assessed by perceived stress and salivary biomarkers) in sedentary middle-aged workers. Considering that combined exercise training enhances parameters related to health in sedentary adults, it was hypothesized that this program would improve the HRQoL domains and reduce participant’s stress levels.

This study evaluated the effects of 16 weeks of combined exercise training on HRQoL and stress levels in sedentary middle-aged workers. The main finding of the present study was that, compared with the control group, the exercise group significantly improved some domains of quality of life, such as the mental component summary and the social functioning subdomain, after 16 weeks of combined training. Higher magnitudes of improvement were found for the mental component summary and mental health subdomain after the exercise program, which resulted in significant differences between the groups. Furthermore, a higher magnitude of improvement was also observed in the exercise group for the role-emotional and vitality subdomain; however, these changes were not significant. Our results failed to show significant changes in physical component summary and its related subdomains. The exercise group perceived reduced stress levels compared to the control group after the 16 weeks of follow-up; however, this change was not significant. No significant effects were observed for salivary stress biomarkers (i.e., cortisol and alpha-amylase). Although our hypothesis was not fully supported, improving the mental domain of HRQoL is paramount in our sample of middle-aged workers.

Our results are consistent with previous studies (Collins et al., 2021; Pietta-Dias et al., 2019; Tozetto et al., 2022) that demonstrate the effectiveness of combined exercise training in improving the mental component of quality of life among middle-aged and older adults. A previous cross-sectional study published in the Lancet Psychiatry also suggested that individuals who exercised 3 to 5 times/week for 30–60 min/session may enhance mental health, reducing mental burden (Chekroud et al., 2018). Likewise, exercise can help relieve several mental disorders, including depression (Harvey et al., 2018) and anxiety conditions (Aylett et al., 2018). In relation to the physical component score and its domains, a slight but not significant decrease in physical role, physical functioning, bodily pain, and the physical component score was observed in the exercise group after 8 weeks of intervention. It is possible that the decrease in bodily pain (indicating more perception of bodily pain) and the other parameters after the 8-weeks of the program is related to resistance training-induced delayed onset of muscle soreness, which is a common effect of few initial training sessions among untrained subjects (Sillanpää et al., 2012) and may persist for 7 days postexercise; later on, muscle soreness usually becomes milder or disappears (Sillanpää et al., 2012; Pearson et al., 2023). The increase in pain perception and decrease in the role-physical assessment by SF-36 have also been previously reported in middle-aged adults by Sillanpää et al. (2012) and Levinger et al. (2007). However, although not significant, a slight increase in physical component and its subdomains were observed for the exercise group after 16 weeks of intervention.

Our results are consistent with a previous study that found that 16 weeks of combined exercise training effectively enhanced the mental component score and its subdomains but not the physical component (except the physical function subdomain) in obese adults (Tozetto et al., 2022). On the other hand, a clinical trial conducted by Collins et al. (2021) found that 8 months of combined exercise training improved both mental and physical component scores, as well as the individual subdomain’s scores of SF-36 among overweight or obese adults at risk of cardiometabolic diseases. Moreover, Baptista et al. (2017) observed that a 24-month multicomponent program (including aerobic, resistance, flexibility, and balance exercises) results in the improvement of three physical subdomains in addition to the physical component score itself but does not improve the mental component score and its subdomains in diabetic older adults. The studies that found significant improvements in the SF-36 physical component applied long-term combined training programs (Collins et al., 2021; Baptista et al., 2017), so it is plausible that the effects of exercise on the physical component are only observed in the long term. In this line, Tozetto et al. (2022) reported that the enhancement of the SF-36 mental component might precede the physical benefits, as they require more stimuli to adapt. In contrast, the increased sense of vigor, the distraction of stressful environments, and belonging to one’s social group are factors that promote psychological wellbeing (Tozetto et al., 2022). According to these authors, the evidence about the effects of combined training interventions on HRQoL physical domain is still inconclusive (Tozetto et al., 2022).

In relation to stress, although not significant, the exercise group tend to improve their perceived stress levels after a 16-week follow-up, while the control group worsened. Moreover, no significant effects were observed for salivary cortisol and alpha-amylase. This trend to decreased perceived stress levels by the exercise group is an important clinical result since psychological stress has a harmful impact on health and wellbeing (O’Connor et al., 2021). Short-term responses to stress include sleep problems (Chen et al., 2023), elevated blood pressure and heart rate, headaches, and unhealthy behaviors such as smoking (Schneiderman et al., 2005). Long-term responses include the increased risk of developing anxiety and depression disorders (Wiegner et al., 2015), cardiovascular diseases (Sara et al., 2018), metabolic syndrome and type 2 diabetes (Harris et al., 2017), and premature mortality (Prior et al., 2016). In the work context, stress and its associated health effects can result in lower productivity from absenteeism and presenteeism and higher healthcare costs (Kuster et al., 2017). A previous study (Silva et al., 2022) in sedentary workers found that the exercise group participants presented lower perceived stress levels after 16 weeks of a home-based combined training program than the control group. Likewise, the same authors did not observe significant changes within groups and differences between groups in cortisol and alpha-amylase levels (Silva et al., 2022). More research is needed to understand the impact of exercise on these markers.

The randomized controlled trial design is one of the strengths of this study. Another important strength was the sample of sedentary middle-aged workers free of major chronic conditions, which reduced the number of potentially eligible participants but increased the representativeness of the HRQoL and stress in this population. Moreover, a supervised exercise intervention designed to meet the total exercise volume recommended by the WHO physical activity guidelines and the optimal adherence to the program are also important strengths. The use of well-validated instruments to assess HRQoL and perceived stress and the 3-times points of assessment is also an important factor.

Nevertheless, some limitations should also be pointed out. Firstly, our sample size calculation was based on the primary outcome of this project (i.e., HOMA-IR), so it is plausible that the lack of an exercise effect on the physical component of HRQoL and stress markers was caused by the study’s small sample size. Secondly, we could not explore subgroup sex differences due to the reduced sample size. Thirdly, the participants’ motivation during the intervention was also not assessed. At the beginning of the intervention, participants were highly motivated; however, the maintenance was challenging in some cases. According to Küüsmaa-Schildt et al. (2019), exercise can improve physical and mental health only when subjects are motivated enough to exercise regularly over a prolonged period. Future controlled studies with large sample sizes should be conducted to better understand the benefits of combined exercise training on the physical component of HRQoL and salivary cortisol and alpha-amylase of stress in middle-aged sedentary workers.

In summary, we found that 16 weeks of combined aerobic and resistance exercise training can positively influence self-rated HRQoL in previously sedentary middle-aged workers, mainly the mental component summary and the social functioning subdomain. Although not significant, the combined training also promoted a clinically relevant reduction of participants’ perceived stress levels after 16 weeks of exercise training compared to the control group. Our findings suggest that middle-aged sedentary workers will likely benefit from a supervised combined exercise regimen to improve HRQoL (i.e., mental health component summary) and wellbeing.