The superiority of Variable Resistance Training (VRT) over traditional Constant Resistance Training (CRT) for enhancing lower-limb performance is debated, with previous meta-analyses limited by aggregating disparate exercises. This systematic review and meta-analysis, the first to focus exclusively on the squat, compared the acute and long-term effects of VRT versus CRT on maximal strength and explosive power. Following PRISMA guidelines, 20 studies were analyzed (literature search up to 15 June 2025), with Hedges’ g used for effect size (ES) calculation. Results demonstrated VRT’s superiority for both acute (ES = 0.34) and long-term adaptations. Acutely, effects peaked with an 8–12 min recovery (ES = 0.43). Long-term, VRT produced greater gains in maximal strength (ES = 0.31) and explosive power (ES = 0.17). Subgroup analyses on maximal strength revealed that elastic bands were highly effective (ES = 0.67), particularly in trained individuals (ES = 0.35), males (ES = 0.41), within cycles < 8 weeks (ES = 0.44), and at frequencies of ≤2 sessions/week (ES = 0.45). For explosive power, chains were most effective (ES = 0.37), significantly improving jumping performance but not sprinting. In conclusion, VRT is a more effective modality for squat training; optimal programs should utilize elastic bands for strength and chains for power, with strength-focused blocks being short-term (<8 weeks) and lower-frequency (≤2 sessions/week) for trained individuals.

Background: Musculoskeletal conditions impose an increasing health burden, particularly in ageing populations. For adults who find it difficult to exercise throughout the week, completing the recommended amount of moderate-to-vigorous physical activity (MVPA) over only 1–2 days, commonly described as the “weekend warrior” (WW) pattern, may offer a more practical approach. Whether this concentrated pattern is associated with musculoskeletal outcomes comparable to those observed with regularly distributed activity remains uncertain. This systematic review synthesized current evidence concerning the relationships of the WW pattern with musculoskeletal outcomes and examined how these associations compared with those observed in inactive (IA) and regularly active (RA) adults. Methods: PubMed, Web of Science, and Scopus were searched from database inception through 30 June 2026, following PRISMA recommendations. Ten observational investigations, including four cohort and six cross-sectional studies, were eligible, with individual sample sizes ranging from 3539 to 83,376 adults. Cohort studies were evaluated using the Newcastle–Ottawa Scale, whereas cross-sectional studies were appraised with the Agency for Healthcare Research and Quality checklist. Results: Across the included studies, adults following a WW pattern generally had more favorable estimates for low bone mineral density (BMD), osteoporosis, osteoarthritis, spinal degenerative changes, inflammatory arthritis, and sarcopenia than inactive adults. Where WW and RA patterns were directly contrasted, their associations with most musculoskeletal outcomes were broadly similar, although WW was associated with a higher hazard of osteoarthritis in one study, a lower hazard of fractures in another, and lower odds of sarcopenia among WW participants. Subgroup analyses further suggested that these associations may vary across population characteristics, although the patterns were not uniform. Associations with BMD tended to be more pronounced in men and in participants with body mass index (BMI) < 25 kg/m². Findings for osteoporosis varied according to age and genetic susceptibility, while age- and sex-specific associations with sarcopenia differed across studies. One exploratory analysis also suggested that the association with osteoporosis may vary according to the timing of MVPA across the day. Conclusions: Meeting the recommended weekly amount of MVPA over 1–2 days was generally associated with more favorable musculoskeletal outcomes than inactivity, while the observed estimates were often close to those reported for regularly distributed activity. These findings support the possibility that achieving sufficient weekly activity may remain relevant even when exercise is concentrated into fewer days. Nevertheless, the evidence is entirely observational and is limited by heterogeneous definitions of WW, differences in physical activity assessment, residual confounding, overlapping study populations, and insufficient investigation of injury outcomes. Current findings therefore cannot establish causality or demonstrate equivalence or non-inferiority between WW and RA patterns.

Background: Although depressive symptoms are common among adolescents who experience school bullying victimization, these symptoms show heterogeneity and seriously affect individuals’ physical and mental health. Our current understanding of the latent classes of depressive symptoms and their transition characteristics over time among adolescents who persistently experience school bullying victimization remains limited. Therefore, it is necessary to use latent transition analysis to identify different depressive symptom patterns and further examine the longitudinal stability and transition trajectories of these patterns. Methods: This retrospective study included 785 adolescents who reported experiencing school bullying victimization at both time points (T1 and T2). Among them, 60.9% were boys, with a mean age of 13.92 ± 1.69 years at T1 and an age range of 11 to 19 years. Participants completed a two-wave survey over a 12-month period. Latent transition analysis (LTA) was conducted to identify latent profiles of depressive symptoms and examine transitions between profiles over time. In addition, physical activity, sleep duration, and substance use were examined as predictors of transitions between depressive symptom profiles. Results: The depressive symptom profiles of adolescents who persistently experienced school bullying victimization were classified into the Low Symptom group, Moderate Symptom group, and High Symptom group. The proportions of these groups were 58.4%, 30.9%, and 10.7% at T1, and 32.1%, 45.3%, and 22.6% at T2, respectively. Overall, the profiles showed either class stability or transitions toward more severe symptom groups, with the High Symptom group showing a 75.8% probability of remaining in the same class at T2. Physical activity, sleep duration, and substance use were all important predictors of depressive symptom transitions among adolescents who persistently experienced bullying victimization. Specifically, physical activity and sleep duration were important protective factors (p < 0.001), whereas substance use was a negative influencing factor (p < 0.001). Conclusions: Depressive symptoms among adolescents who persistently experience bullying victimization show dynamic transition characteristics, and health behaviors significantly influence symptom evolution. These findings suggest that interventions should focus on improving health behaviors to alleviate or prevent the worsening of depressive symptoms.

Objective: This study aimed to examine the mediating role of Internet Addiction in the association between bullying victimization and Depressive Symptoms among left-behind children, as well as the moderating role of physical activity in this relationship. Methods: A cross-sectional design was adopted. A total of 21,689 left-behind children were recruited using stratified random sampling. A moderated mediation model was constructed within the generalized linear model framework. Conditional indirect effects and the probability scale were further used to analyze the relationships among bullying victimization, Internet Addiction, physical activity, and Depressive Symptoms in left-behind children. Results: After controlling for confounding factors, bullying victimization significantly predicted Depressive Symptoms among left-behind children (B = 1.179, p < 0.001). Internet Addiction partially mediated the association between bullying victimization and Depressive Symptoms. Specifically, bullying victimization significantly predicted Internet Addiction among left-behind children (B = 1.041, p < 0.001), and Internet Addiction significantly predicted Depressive Symptoms (B = 1.218, p < 0.001). Moreover, physical activity significantly moderated the association between bullying victimization and Internet Addiction (p < 0.05). Conclusion: Among left-behind children, bullying victimization may increase the risk of Depressive Symptoms partly by triggering Internet Addiction, while physical activity may buffer the association between bullying victimization and Internet Addiction.