A quantitative, cross-sectional research design was employed to investigate the associations between school backpack loading, sitting time and LBP among schoolchildren. The design was suitable for identifying prevalence and relationships between categorical health-related variables in a natural school setting.

The study was conducted between August and September 2022 among primary schools in Gaborone, Botswana. Schools were randomly selected from five geographical clusters to ensure diverse socioeconomic representation. The target population consisted of children aged 10–12 years attending grades 5 and 6. A total of 521 participants (46% boys, 54% girls; mean age = 11.14 ± 0.74 years) were included in the final analysis. The initial estimated sample size of 543 was based on a 95% confidence level, a 5% margin of error and an anticipated response rate of 80%, ensuring adequate statistical power. Inclusion criteria required participants to be apparently healthy (i.e. children without known medical conditions or musculoskeletal disorders that could affect normal school participation, based on school records and self-report), to use school backpacks daily and to have obtained written parental consent and child assent. Children with physical disabilities or known spinal deformities were excluded based on available school records and participant and/or teacher reporting, as no clinical screening was conducted.

Three validated instruments were employed:

Following institutional and governmental permissions, the researcher visited each selected school to introduce the study. The purpose and procedures were explained to teachers, parents and participants to ensure comprehension and voluntary participation. Data collection was conducted in classrooms by the primary researcher, assisted by trained research assistants, under standardised conditions. Research assistants were trained prior to data collection to ensure consistency in questionnaire administration and measurement procedures. Participants completed the YSQ and IPAQ-SF individually, with trained research assistants available to clarify items. Anthropometric and backpack measurements were recorded immediately afterwards. The entire process, including briefing and completion, took approximately 45 min/class.

Data were analysed using the Statistical Package for the Social Sciences (SPSS) version 29.0 (IBM, Armonk, NY, United States). Descriptive statistics were used to summarise demographic characteristics and main study variables. Missing data were present primarily for the sitting time variable and, to a lesser extent, for LBP variables. Analyses were conducted on valid cases only, using listwise deletion for the relevant cross-tabulations. Accordingly, the denominators for LBP frequency, LBP intensity and sitting time differ across analyses, and these valid sample sizes are reported in the Results section and accompanying tables. To meet the assumptions for cross-tabulation, LBP frequency was recoded into two categories: No or infrequent pain (combining ‘never’ and ‘rarely’) and frequent pain (combining ‘sometimes’ and ‘often’). Low back pain intensity was similarly categorised as no-to-mild pain (none, very mild, mild) and moderate-to-severe pain (moderate, severe, very severe). Chi-square (χ²) tests were used to assess associations between LBP outcomes and categorical predictors (age, sex, backpack mass and sitting time). Assumptions for chi-square analyses, including expected cell counts, were evaluated prior to analysis, and category collapsing was applied where necessary. Effect sizes were interpreted using Phi (Φ) or Cramér’s V, with the following thresholds: 0–0.10 = very weak, 0.10–0.30 = weak, 0.30–0.50 = moderate, 0.50–0.70 = strong, ≥ 0.70 = very strong association. Statistical significance was accepted at p < 0.05.

Ethical clearance was granted by the Health Research Ethics Committee (HREC) of the North-West University (reference: NWU-00185-21-A1) and approved by the Botswana Ministry of Education and participating schools. Written parental consent and child assent were obtained prior to the participant’s involvement. Confidentiality and anonymity were maintained throughout the study, and participants could withdraw at any time without consequence.

A total of 521 schoolchildren (mean age: 11.14 ± 0.74 years) participated in the study. The sample comprised 46% boys (n = 240) and 54% girls (n = 281). The mean body mass was 42.26 kg ± 9.58 kg, and the mean backpack mass was 4.04 kg ± 1.32 kg, corresponding to 9.95 ± 3.78% of body mass. Based on classification criteria, 43% of participants (n = 225) carried backpacks weighing ≥ 10% of their body mass.

Self-reported weekday sitting time averaged 7.39 ± 2.43 h/day. However, sitting time data were available for only 200 participants (38%), with 321 participants (62%) having missing data. Among those with valid responses, 60% (n = 121) reported sitting for less than 8 h/day, while 40% (n = 79) reported sitting for 8 h/day or more.

Low back pain frequency data were available for 484 participants (93%), with 37 (7%) missing responses. Among valid responses, 41% (n = 199) reported never experiencing LBP, 22% (n = 107) rarely, 28% (n = 134) sometimes and 9% (n = 44) often. When categorised for analysis, 63% of participants were classified as having no or infrequent LBP, while 37% were classified as having frequent LBP.

Low back pain intensity data were available for 484 participants (93%), with 7% missing. Among valid responses, 41% (n = 200) reported no pain, 28% (n = 135) very mild pain, 15% (n = 73) mild pain, 9% (n = 45) moderate pain, 4% (n = 18) severe pain and 3% (n = 13) very severe pain. For analytical purposes, 78% of participants were classified as experiencing no-to-mild pain, while 14% were classified as having moderate-to-severe pain.

Table 2 presents the associations between LBP frequency and selected categorical variables. A statistically significant association was observed between backpack mass classification and LBP frequency (χ² = 4.052, p = 0.044), with a small effect size (Φ = 0.09). A higher proportion of frequent LBP was observed among children carrying backpacks weighing ≥ 10% of their body mass (12.6%) compared to those carrying lighter loads (7.2%).

Table 3 presents the associations between LBP intensity and categorical variables. No statistically significant associations were observed between LBP intensity and age (χ² = 2.865, p = 0.239; V = 0.08), sex (χ² = 0.151, p = 0.698; Φ = 0.02), backpack mass classification (χ² = 0.007, p = 0.934; Φ = 0.00) or sitting time classification (χ² = 0.314, p = 0.575; Φ = 0.04).

The main finding of this study was that backpack mass was significantly, albeit weakly, associated with LBP frequency. Heavier backpacks were linked to more frequent LBP episodes among children aged 10–12 years. In contrast, no significant associations were found between sitting time, age or sex and either LBP frequency or intensity.

The findings on backpack loading are consistent with the existing literature, indicating that excessive schoolbag weight may contribute to musculoskeletal discomfort in children. Previous studies have demonstrated that loads exceeding 10% – 15% of body weight are associated with alterations in posture, gait mechanics and spinal loading (Brackley & Stevenson 2004; Cuenca-Martínez et al. 2023). Experimental evidence further suggests that increased backpack loads result in forward trunk inclination, altered balance and increased plantar pressure, which may contribute to musculoskeletal strain (Bukowska et al. 2021; Tomal et al. 2022). In the present study, although backpack load was associated with LBP frequency, the relatively weak association suggests that load alone may not sufficiently explain the occurrence of pain. This aligns with previous research reporting inconsistent associations between backpack weight and LBP, suggesting that factors such as posture, duration of carriage, physical conditioning and individual susceptibility may moderate this relationship (Dianat et al. 2013; Sankaran et al. 2021).

Sedentary behaviour was also examined in relation to LBP; however, no significant associations were observed. This aligns with recent literature suggesting that prolonged sitting may contribute to musculoskeletal discomfort through increased spinal loading, reduced trunk muscle activation and sustained static postures (Da Costa et al. 2022; Mahdavi et al. 2022). However, the current findings align with previous systematic reviews, which indicate that the relationship between sedentary behaviour and spinal pain is generally weak and inconsistent (Montgomery et al. 2024). This suggests that sitting duration alone is unlikely to be an independent determinant of LBP but may interact with factors such as posture quality, physical activity levels and ergonomic conditions. Together, these findings reinforce the idea that single behavioural exposures may not independently explain LBP risk in children.

Importantly, these findings should be interpreted within the specific school context of Botswana, where environmental and infrastructural factors may influence both backpack use and sedentary behaviour. Limited access to storage facilities, the need to transport multiple textbooks daily and prolonged classroom-based learning may contribute to sustained mechanical loading of the spine. In addition, variability in classroom ergonomics and seating design may further exacerbate postural strain during extended periods of sitting. These contextual factors may interact with individual biomechanical and behavioural characteristics, potentially explaining the weak but significant association observed between backpack load and LBP frequency. This highlights the importance of considering both environmental and individual-level determinants when addressing musculoskeletal health in school-aged populations.

No significant associations were observed for age or sex, suggesting that biomechanical and behavioural factors may be more relevant determinants of LBP at this stage of development.

This study has several strengths, including the concurrent assessment of both mechanical (backpack load) and behavioural (sitting time) factors associated with LBP in a previously under-researched population. The relatively large sample size and objective measurement of backpack and body mass further strengthen the robustness of the findings. However, certain limitations should be acknowledged. The cross-sectional design limits causal inference, and reliance on self-reported measures may introduce recall and reporting bias. In addition, sitting time data were available only for a subset of participants, which may limit the generalisability of findings on sedentary behaviour. Unmeasured factors such as psychosocial influences, physical fitness and growth-related changes may also contribute to LBP and were not accounted for in the present study. Although the YSQ and IPAQ-SF are validated instruments, no formal cultural adaptation or validation was conducted within the Botswana context, which may have influenced comprehension, response accuracy and the validity of self-reported data. Future research should consider longitudinal designs and objective measures of sedentary behaviour to better understand causal pathways.

From a practical perspective, these findings suggest that interventions to reduce LBP among schoolchildren should adopt a multifactorial approach. Strategies may include promoting appropriate backpack loading practices; encouraging regular movement and breaks from prolonged sitting; participating in physical activity, exercise or active play during breaks and improving classroom ergonomics. Educational initiatives targeting both learners and educators may be beneficial in promoting healthy posture and movement behaviours within the school environment.