In adolescents, the relationship between physical activity and academic performance has received considerable attention (Haapala, 2012; Kalantari and Esmaeilzadeh, 2016) in the same way as physical fitness and academic performance (Suchert et al., 2016; Ruiz-Ariza et al., 2017) or muscular fitness (MF) and academic performance (Muntaner-Mas et al., 2018). In this field, the benefits of resistance training on the neuromuscular system are well documented, and there is increasing evidence that it can induce neuroplastic changes in the nervous system and improve cognitive and mental function (Chow et al., 2021). The mental health benefits of aerobic-based physical activity have been reported in the literature (Kandola et al., 2016; Northey et al., 2018). Specifically, strength training is an important variable for the improvement of cognitive performance, including a transcendental aspect that is the deterioration in memory and central executive functioning with age (Frith and Loprinzi, 2018). According to a systematic review with meta-analysis by Robinson et al. (2023), resistance training may have a positive effect on overall cognitive, academic and on-task behaviors in schoolchildren; however, MF is associated with cognition and academic performance. Other studies, such as Gordon et al. (2017) and Bennie et al. (2020), have pointed out how strength training also has benefits on a psychological level (e.g., mental health), reducing symptoms of depression and anxiety and hence another essential aspect to consider.

According to the recommendations of the World Health Organization (2020), it is necessary to include strength training on a regular basis to achieve health benefits. According to these recommendations, children and adolescents between 5 and 17 years old should engage in at least 60 minutes a day of moderate to vigorous physical activity and participate in 3 days a week of resistance work to strengthen their muscles and bones. This training could improve physical fitness, cardiometabolic health, bone health, mental health, and cognitive outcomes such as executive function (Muñoz-Parreño et al., 2021; Chen et al., 2023) or academic performance (Xu and Sun, 2023). In this field, physical fitness includes cardiorespiratory endurance, MF, muscular endurance, and flexibility (Faigenbaum et al., 2020). García-Hermoso et al. (2019) reported that MF had a negative association with adiposity and cardiometabolic disease risk score and a positive association with bone health. In support of this notion, scientific evidence has shown that strength training is beneficial for the development of children and young people, and many benefits are recommended to include it in physical education lessons through pedagogical activities and adapted strategies (Dos Santos et al., 2022), considering that physical fitness has an important role in mediating the association between physical activity and academic achievement via higher levels of fitness, including aerobic performance and strength (Syväoja et al., 2018).

Similarly, it is necessary to specify the definition of academic performance. Academic performance is assessed by computing the grade point average of all school subjects (Suchert et al., 2016; Hsieh et al., 2018; Martinez-Zamora et al., 2021), the grade obtained in language, maths and foreign language (English), and the grade point average of these subjects (Muntaner-Mas et al., 2021; Tapia-Serrano et al., 2021) or standardized tests (Raine et al., 2018). Other study (Manzano-Sánchez et al., 2020) has assessed physical education performance with the grades reported at the end of the course and in each quarter. Moreover, academic performance is related to physical fitness, considering body mass index (BMI), MF, aerobic endurance of primary school students (Xu and Sun, 2023), aerobic endurance, MF, and agility (Hansen, 2017), and junior high school students aged 12 to 15  years (Hsieh et al., 2018). Finally, MF is a variable associated with cognitive performance, but this effect appears to be independent of age, physical activity and other covariates (Frith and Loprinzi, 2018).

Previous studies have examined the relationship between MF and academic performance (Padilla-Moledo et al., 2012; Esteban-Cornejo et al., 2014; García-Hermoso et al., 2017; Gil-Espinosa et al., 2020). For instance, some papers have examined the relationships between both upper and lower body muscular strength and academic performance (Padilla-Moledo et al., 2012; Esteban-Cornejo et al., 2014; Muntaner-Mas et al., 2018) and between lower body muscular strength and other factors (García-Hermoso et al., 2018; Gil-Espinosa et al., 2020) in the young population. Furthermore, only the studies by Gil-Espinosa et al. (2020) and Muntaner-Mas et al. (2018) included academic performance in physical education. Handgrip strength is commonly used as a proxy of total MF because it is strongly correlated in adolescents (Wind et al., 2010; Weedon et al., 2022; De Almeida Santana et al., 2023). Moreover, equal consideration of lower body muscular strength is also relevant since it is strongly associated with other tests that assess both upper and lower body muscular strength (Castro-Piñero et al., 2010). Therefore, combining the handgrip strength test and the standing long jump could provide a more comprehensive measure of global MF than evaluating these components separately. To our knowledge, there are no previous studies evaluating MF (combining both upper and lower body muscular strength) with performance in some specific school subjects (including physical education). Only the study by Muntaner-Mas et al. (2018) assessed the relationship between MF (including both upper and lower muscular strength) and academic performance in physical education. However, these authors did not discuss this specific result and did not stratify the analyses by sex. Therefore, the aim of this study was to examine the association between MF and academic performance according to the grade achieved in language, math, foreign language and physical education and the average global score in a sample of Spanish secondary school students.

Table 1 shows the descriptive data of the study participants based on their MF status and stratified by sex. For both sexes, the highest GPA was observed for adolescents with a high MF (boys: median = 6.8, IQR = 2.8; girls: median = 7.6, IQR = 2.2). The lowest GPA was identified for adolescents with low MF (median = 6.2, IQR = 2.3). Conversely, in girls, the lowest GPA was found in those with medium MF (median = 6.9, IQR = 2.7).

Figure 1 shows the estimated marginal means from the GAMs for GPA based on MF (z score) by sex. The approximate significance of smooth terms was significant for both sexes (p < 0.05). A nonlinear association between MF and GPA was identified. Overall, in both sexes, participants with the highest MF z scores had the greatest GPA scores.

Table 2 displays the estimated marginal means of different school subjects (i.e., language, math, English, and physical education) based on MF status by sex. Overall, adolescents with high MF showed the highest means for all the individual school subjects examined. The only exception was for language in boys. For boys, significant differences were found for physical education between adolescents with medium MF (mean (M) = 6.7, 95% BCa CI 6.3–7.1) and those with high MF (M = 7.5, 95% BCa CI 7.1–7.9). In girls, significant differences were also identified for physical education between adolescents with low MF (M = 6.9, 95% BCa CI 6.6–7.2) and their counterparts with high MF (M = 7.6, 95% BCa CI 7.3–7.9).

The estimated marginal means of GPA and their BCa bootstrapped 95% CIs according to MF status (stratified by sex) are shown in Figure 2. For boys, although no significant differences were found among the different MF statuses, the highest GPA mean was identified in adolescents with high MF (M = 6.8, 95% BCa bootstrapped CI 6.4–7.1). For girls, the highest mean GPA was observed for those with high MF (M = 7.4, 95% BCa bootstrapped CI 7.1–7.7), with significant differences between these participants and their counterparts with low MF (p = 0.008) and those with medium MF (p = 0.017).

The aim of this study was to examine the associations between MF (upper and low strength) and overall academic performance and individual school subjects (i.e., language, math, foreign language, and physical education). To our knowledge, only one study from Muntaner-Mas et al. (2018) assessed the relationship between MF (including both upper and lower body muscle strength simultaneously) and academic performance in physical education. Although the relationship between MF and academic performance was not linear, we observed that boys and girls with the highest levels of MF obtained higher school grades. The almost linear relationship we observed in girls seems to suggest that the potential benefits of having a higher MF in terms of overall academic performance could be greater in girls. Dividing MF according to tertiles, we observed that there were significant differences in overall academic performance, but only for girls.

In terms of specific subjects, we observed that the largest differences occurred in physical education grades. These results are in line with the scientific literature, which suggests that a higher MF is related to greater academic performance (de Almeida Santana et al., 2023; Robinson et al., 2023). Conversely, another review concluded that this relationship was not evident (Segura-Díaz et al., 2021). The relationship between greater MF and greater academic performance in adolescents may be linked to various interconnected factors. MF is correlated with several variables, such as sport participation, active transport and physical activity. However, this variable has been studied to the greatest extent and has been shown to be the most influential variable in MF, especially during vigorous exercise (Smith et al., 2019). For this reason, although the exact connection may vary from individual to individual, there are several possible reasons for these findings related to physical exercise.

Physical exercise (including strength training) has been shown to have significant benefits on both academic performance (Cappelen et al., 2017; Li et al., 2021) and cognitive function (Biddle et al., 2019; Alexander and Allendorfer, 2023; Logan et al., 2023). It is possible that physical exercise increases neurogenesis and angiogenesis, increases mitochondrial biogenesis and antioxidant enzyme activity, and provides energy to the brain because of the production of lactate; additionally, physical exercise allows the release of anti-inflammatory cytokines that reduce neuroinflammation (Chen and Nakagawa, 2023). Another possible explanation is that this relationship could be related to insulin-like growth factor-1 (IGF-1). Resistance training increases the release of IGF-1, which can promote the growth and survival of neurons and improve brain plasticity and executive functions (Cassilhas et al., 2007; Xu and Sun, 2023).

On the other hand, physical exercise seems to reduce stress, depression and anxiety in the general population (McDowell et al., 2019; Singh et al., 2023), in children and young people (Carter et al., 2021), and in people with mental health disorders or chronic diseases (Singh et al., 2023). Supporting this notion, Teferi (2020) and Ferreira et al. (2021) concluded that physical exercise could influence anxiety or depression with a moderate-small effect and could influence academic performance. However, caution is required to interpret this hypothesis because the effect sizes ranged from small to moderate, and considerable inconsistency in results among studies was identified (Ferreira et al., 2021).

The benefits of strength training for children and adolescents include improvements in health, fitness, injury prevention and rehabilitation (Stricker et al., 2020) and physical literacy (Zwolski et al., 2017), which may have important effects on the academic performance of students (Domínguez-Martín et al., 2024). The relationship between physical activity programs and physical activity level could increase social–emotional skills (Taylor et al., 2017) with opportunities to interact and communicate between students (Goh et al., 2022), and these social–emotional skills may be transferable to the academic environment, improving adolescents’ ability to manage time, set goals, and collaborate with others. Therefore, establishing healthy routines such as regular strength training could include healthy habits such as regular sleep habits (Urrila et al., 2017; Santos et al., 2023) or paying attention to nutrition, which plays a crucial role in facilitating the smooth growth and development of brain organs (Athaya et al., 2023) and academic performance.

Regarding sex, Álvarez-Bueno et al. (2020) noted that although physical fitness was positively associated with academic performance in both sexes, these associations were stronger in boys than in girls. Similarly, Janak et al. (2014) also reported that regardless of sex and educational stage, students with greater physical fitness showed greater performance in cognitive aptitude tests, but there were no differences between the sexes. Conversely, Padilla-Moledo et al. (2012) did not identify an interaction effect between sex and MF in relation to academic performance. These contradictory results may be due to the way participants’ physical fitness was assessed. Another possible explanation for the difference in our study due to the more favorable results in girls could be that stress and anxiety levels are generally greater in females than in males (Gao et al., 2020).

In relation to specific subjects, our results agreed with a previous study that observed a positive relationship between MF and physical education (Muntaner-Mas et al., 2018) but disagreed with other (Gil-Espinosa et al., 2020). However, Gil-Espinosa et al. (2020) included physical education with the rest of the participants separately, and the relationship between MF and academic performance was not significant in physical education, but it was significant in other subjects (i.e., math). On the other hand, Muntaner-Mas et al. (2018) showed that cardiorespiratory fitness was associated with overall academic performance, but only MF was individually linked with physical education (and math). One possible explanation could be related to the fact that this subject contributes to increasing MF (García-Hermoso et al., 2020) or because individuals with a higher MF may have greater interest in the subject that revolves around the body and movement according to the Committee on Physical Activity and Physical Education in the School Environment, Food and Nutrition Board, and Institute of Medicine (2013). As previously mentioned, greater physical literacy is related to greater academic performance (Domínguez-Martín et al., 2024), which could also explain this result.

The main conclusions of the study corroborate that MF is related to academic performance both in general and specifically in the context of physical education. At the same time, although the association appears to follow the same trend for both sexes, the results seem more evident for girls. However, it is interesting to consider future studies that include other variables, such as BMI or the level of aerobic fitness, given that various investigations have considered these two variables, making it necessary to use valid instruments such as manual dynamometry or a long jump to assess strength performance in students.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics Committee of the Albacete University Hospital Complex and the Albacete Integrated Care Management, granted approval for this study (approval IDs: 2218/2018, 2021-85). The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants’ legal guardians/next of kin.

DM-S: Writing – original draft, Methodology, Conceptualization. HG-E: Writing – review & editing. JL-G: Writing – review & editing, Project administration, Methodology, Formal analysis.