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Background: The incidence of low-back pain (LBP)is high among elite male high school soft tennis players. A previous report showed that hip internal-rotation (IR) restriction in the non-dominant leg could increase the risk of LBP. Moreover, IR in the dominant shoulder is important for serve and stroke movements, suggesting that IR restriction in the dominant shoulder can contribute to LBP. The simultaneous incidence of non-dominant-hip IR restriction may help in developing a good LBP-related factor model; therefore, this study aimed to investigate the association between dominant-shoulder IR restriction and LBP in elite male high school soft tennis players., Design: This is a single-center cross-sectional study., Methods: This study included 176 male high school soft tennis players from 14 elite teams. The main measures were IR and external-rotation range of motion (ROM) in the dominant and non-dominant shoulders and hip, assessed using a goniometer with a bubble attached. Multiple logistic regression analyses were performed with the presence of LBP as a categorical variable (LBP, 1; non-LBP (NLBP), 0). Multiple logistic regression models were created as follows: Model 1 included dominant-shoulder IR restriction (loss of glenohumeral IR (GIRLoss)), Model 2 included non-dominant-hip IR ROM, and Model 3 included both GIRLoss and non-dominant-hip IR ROM as the main explanatory variables to test the association between dominant-shoulder IR restriction and LBP, compare its suitability as an associated factor with non-dominant-hip IR restriction, and determine if either or both should be considered in an LBP association model based on model fit. The significance of each multiple logistic regression model was examined using the model χ 2 test, and a model with P<0.05 was judged as a significant model. Model fit was examined using the Hosmer-Lemeshow test, and P≥0.05 was judged as a good model fit. The Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) were used to compare the goodness-of-fit among multiple logistic regression models.  Results: The LBP and non-LBP groups comprised 59 and 117 players, respectively. GIRLoss in the dominant shoulder was a significant independent factor (odds ratio: 1.06, 95% CI: 1.02-1.09; P<0.01) in Model 3, which included hip IR restriction in the non-dominant leg (odds ratio: 0.90, 95% CI: 0.86-0.94; P<0.01). In all models, the explanatory variables fitted were significantly associated with LBP, indicating that the models were significant and fitted well: the AICs (and BICs) for Models 1, 2, and 3 were 198.4 (207.6), 178.6 (187.9), and 168.8 (181.1), respectively, indicating that Model 3 was the best fit., Conclusions: In elite male high school soft tennis players, IR restriction in the dominant shoulder was associated with LBP. IR restriction in the dominant shoulder and non-dominant hip as a significant factor for LBP may contribute to developing an optimal multiple logistic regression model for LBP., Competing Interests: Human subjects: Consent was obtained or waived by all participants in this study. Ethics Review Committee of the Nittaduka Medical Welfare Center issued approval 2019-56. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Tanabe et al.)

Context: The incidence of low back pain (LBP) is high among high school male soft tennis players. In some sports for which the rotational component of the body is important, an association between restricted hip internal rotation of the nondominant leg and LBP has been reported; however, whether this association holds in soft tennis is unknown. Therefore, this study aimed to evaluate the association between hip internal rotation, hip external rotation, hamstring flexibility, iliopsoas flexibility, and LBP incidence., Design: This study was designed as a cross-sectional study, conducted at a sports training center., Methods: Participants comprised 113 male elite high school soft tennis players (age: 16.1 [0.7] y) from 9 elite-level teams. The main outcome measures were the hip internal and external rotation range of motion, hamstring flexibility on the straight leg raise test, and iliopsoas flexibility on the Thomas test. Multiple logistic regression analysis was performed to examine the influence of main outcomes on LBP incidence in the past 1 year., Results: A total of 35 participants had LBP (LBP group); 78 participants did not have LBP (non-LBP group). Multiple logistic regression analysis revealed that the odds ratio for height was 1.08 (95% confidence interval, 1.00-1.16; P = .043) and for the hip internal rotation range of motion in the nondominant leg was 0.90 (95% confidence interval, 0.85-0.95; P < .001), indicating significant associations with LBP., Conclusion: Hip internal rotation range of motion in the nondominant leg and height were crucial factors related to LBP in male elite high school soft tennis players.