Abstract
Background
Low back pain (LBP) is common in young athletes and may restrict participation in basketball. Evidence regarding the association between lower extremity tightness and LBP in adolescent basketball players remains limited. This study aimed to examine whether anterior (quadriceps) and posterior (hamstring) thigh tightness were associated with LBP in elementary and middle school players.
Methods
In this cross-sectional study conducted in Fukushima, Japan (2013–2014), players completed questionnaires on the presence or absence of lifetime and point prevalence of LBP. Physiotherapists assessed mechanically provoked LBP (induced by lumbar flexion and extension), as well as anterior and posterior thigh tightness. Anterior thigh tightness was defined as a heel-buttock distance (HBD) > 0 cm, and posterior thigh tightness as a sit-and-reach (SR) value below the age- and sex-specific mean − 1 standard deviation (SD). Multivariable logistic regression was used to examine the association between anterior and posterior thigh tightness and lifetime LBP, adjusting for school level, sex, training days per week, years of play, current knee pain, and body mass index. Statistical significance was set at p < 0.05.
Results
Of the 385 participants, 324 players (mean age: 11.1 years; 39.8% male) were included in the analysis. The lifetime prevalence of LBP was 19.8%, the point prevalence was 4.6%, and the prevalence of LBP with lumbar extension and flexion were 15.7% and 4.0%, respectively. Anterior and posterior thigh tightness were present in 68.8% and 44.8% of players, respectively. In univariable analyses, players with posterior thigh tightness had higher prevalences of lifetime and current LBP and more frequently required rest from play. Multivariable analysis showed that posterior thigh tightness was independently associated with lifetime LBP (odds ratio: 2.11; 95% confidence interval: 1.07–4.15). In contrast, anterior thigh tightness was not significantly associated with LBP (odds ratio: 0.82; 95% confidence interval: 0.40–1.68).
Conclusions
Posterior thigh (hamstring) tightness was independently associated with lifetime LBP in young basketball players. Longitudinal studies are needed to determine temporality and causality.
Supplementary Information
The online version contains supplementary material available at 10.1186/s13102-026-01752-3.
Keywords: Adolescent athletes, Basketball, Low back pain, Hamstring tightness, Sit‑and‑reach distance
Background
Low back pain (LBP) is common in childhood and adolescence and may limit sports participation [1, 2]. Several competitive sports pose risks for LBP in school children [3–6]. Basketball, one of the most popular sports globally, exposes young athletes to physical stress during critical growth stages, and LBP is highly prevalent among basketball players [7–10]. Large-scale studies have identified several factors associated with LBP in young athletes, including age, sex [11, 12], and training volume [12]. Additionally, physical impairments, such as reduced flexibility, are considered important factors associated with LBP in various sports [13].
In basketball, frequent jumping, abrupt decelerations, pivots, and landings transmit ground reaction forces through the lower extremities to the lumbar spine. Lower extremity function is considered important for controlling impact on the lower back [14]. Specifically, tightness in the lower extremity muscles can alter lumbopelvic mechanics and increase lumbar load [15]. For instance, posterior thigh (hamstring) tightness can restrict pelvic mobility, leading to compensatory lumbar flexion during bending or landing tasks, which increases mechanical stress on the lumbar spine [16, 17]. Similarly, anterior thigh (quadriceps) tightness may limit hip extension and cause compensatory lumbar hyperextension [18, 19]. Although several studies have reported that lower extremity tightness is associated with LBP in athletes [15, 18–21], most of this evidence comes from asymmetric throwing sports, such as baseball and softball [18, 19, 21].
Despite the unique biomechanical demands of basketball, the specific relationship between lower extremity tightness—particularly the combined assessment of anterior and posterior thigh tightness—and LBP in young (elementary and middle school) basketball players remains underexplored. It is unclear whether the associations observed in asymmetric throwing sports or older athletes apply to young athletes engaged in multidirectional jumping sports. Therefore, in this study, we aimed to investigate the association between anterior and posterior thigh tightness and LBP in young basketball players. We hypothesized that anterior and posterior thigh tightness are significantly associated with LBP in this population. By clarifying the sport-specific physical factors associated with LBP in this growing population, our findings may provide novel insights into the pathomechanisms of LBP in youth basketball.
Methods
This study was approved by the Ethics Committee of our institution (approval number: 2160) and was conducted in accordance with the Declaration of Helsinki. Basketball players who participated in basketball training sessions held in Aizuwakamatsu City and Nihonmatsu City, Fukushima, Japan, during the 2013–2014 season were enrolled. Written informed consent to participate in the study was obtained from all participants and their guardians. The participants belonged to local youth basketball clubs. Physiotherapists provided medical checkups during the training sessions. Self-reported questionnaires were distributed to the participants before the medical checkup and collected on the checkup day. The questionnaire included questions on basketball career, playing position, number of training days, total training time per week, and history of LBP, knee pain, and ankle pain (Additional file 1). Physical examinations assessed spinal motion and lower extremity tightness. All physical examinations were performed by physiotherapists who were blinded to the participants’ questionnaire responses. To ensure measurement consistency, all participating physiotherapists completed a standardized training session on the assessment procedures prior to the medical checkups.
Assessment procedure
Assessment of low back pain
LBP was defined as pain localized between the lower margin of the 12th rib and the inferior gluteal folds, as indicated by a simple figure [22]. Lifetime and point prevalences of LBP were assessed using a self-reported questionnaire. Lifetime LBP was defined as “having ever experienced LBP,” and point LBP as “having LBP at the exact time of the medical checkup.” We also investigated whether players had to refrain from playing because of LBP. LBP with lumbar motion was defined as LBP induced by lumbar flexion or extension during physical examination.
It was assessed in a relaxed standing position, with participants’ feet positioned shoulder-width apart. Physiotherapists passively moved the lumbar spine into flexion or extension to the participants’ limits while keeping their knees straight. A positive response was recorded when LBP was elicited [19, 21].
Assessment of lower extremity tightness
The heel-buttock distance (HBD) was measured to evaluate anterior thigh (quadriceps femoris) tightness. It was measured in the prone position, with the knee passively flexed until resistance was felt by the examiner, who then measured the distance between the heel and buttocks (Fig. 1A). Players with an HBD greater than 0 cm on either side were defined as having anterior thigh tightness [18, 21]. Sit-and-reach (SR) flexibility was assessed to evaluate posterior thigh (hamstring) flexibility [23]. Participants were required to sit with their backs against a wall, knees straight, legs together, and hands placed on the equipment with elbows extended (Fig. 1B). They were then asked to bend forward as far as possible and hold the position for approximately 2 s (Fig. 1B). The final position attained was recorded as the test score. Mean values and standard deviations (SDs) for the SR distance by age and sex were obtained from an external, nationwide survey of Japanese students (see Additional file 2). To identify players with flexibility clearly below the population average, posterior thigh tightness was operationally defined as a value below the mean minus 1 SD for age and sex.
Fig. 1.
Assessment procedures for lower extremity tightness. A Heel-buttock distance (HBD) measurement for anterior thigh tightness. B Sit-and-reach (SR) test for posterior thigh tightness
Assessment of height and body weight
Height was classified based on age- and sex-specific means and SDs derived from a nationwide government survey in Japan (see Additional file 3). Individuals with height within the mean ± 1 SD were defined as average; values > + 1 SD as tall, and values < − 1 SD as short. Body mass index (BMI) was used as an indicator of appropriate body weight. Based on previous reports by Cole et al. [24], age- and sex-specific BMI cutoff values for overweight and underweight children were applied.
Statistical analysis
Statistical analyses were performed using the chi-squared test for categorical variables and the Wilcoxon test for continuous variables. To evaluate the association between LBP and lower extremity tightness, logistic regression analysis was conducted. Lifetime LBP was designated as the primary outcome, and anterior and posterior thigh tightness were included simultaneously as the primary exposures. Secondary outcomes included current LBP and LBP with lumbar flexion and extension. The model was adjusted for school level (elementary vs. junior high school), sex, training days per week, years of play, current knee pain, and BMI. Statistical analyses were performed using JMP software (version 15.0; SAS Institute, Cary, NC, USA). A p-value of less than 0.05 was considered statistically significant.
Results
Of the 385 basketball players who participated in the training sessions, three were excluded because of incomplete questionnaire data, and 58 were excluded because they did not participate in the physical examination owing to scheduling constraints. Ultimately, 324 players (129 males and 195 females) with a mean age of 11.1 ± 1.6 years (range: 7–14 years) were included in the analysis (Fig. 2). A comparison of included (n = 324) and excluded (n = 58) players using available questionnaire data showed that excluded players were significantly younger, exclusively elementary school students, and more frequently male (all p < 0.05). However, there was no significant difference in the prevalence of lifetime LBP between the two groups (19.8% vs. 13.8%, p = 0.285). Detailed comparisons are provided in Additional file 4.
Fig. 2.
Flowchart of participant recruitment of the 385 participants in the training session, 324 were included in the analysis after excluding three with incomplete questionnaire responses and 58 who did not undergo physical assessments
Prevalence of LBP and lower extremity tightness
The prevalence of LBP subtypes and lower extremity tightness is summarized in Table 1. Notably, overall, 29 players (9.0% of the full sample; 45.3% of those with lifetime LBP) reported stopping basketball because symptoms interfered with performance. Of the 324 players, 223 (68.8%) had anterior thigh tightness and 145 (44.8%) had posterior thigh tightness. The mean [SD] of the SR distance for our study sample was 31.1 [6.5] cm for males and 32.2 [8.5] cm for females.
Table 1.
Demographic characteristics of the participants
| Mean [SD], n (%) | ||
|---|---|---|
| Number | 324 | |
| Age (year) | 11.1 [1.6] | |
| School | Elementary school | 263 (81.2) |
| Junior high school | 61 (18.8) | |
| Sex | Male | 129 (39.8) |
| Female | 195 (60.2) | |
| Basketball career (year) | 2.6 [1.6] | |
| Start age (year) | 8.5 [1.8] | |
| Position | Guard | 60 (18.5) |
| Forward | 37 (11.4) | |
| Center | 46 (14.2) | |
| Not fixed | 181 (55.9) | |
| Training time (h) | 9.7 [4.2] | |
| Training days | 4.2 [1.2] | |
| BMI | 17.5 [4.0] | |
| Overweight (BMI > 22) | 20 (6.3) | |
| Underweight (BMI < 13.5) | 3 (0.9) | |
| Low back pain | Lifetime | 64 (19.8) |
| Current | 15 (4.6) | |
| Need for rest | 29 (9.0) | |
| With flexion | 13 (4.0) | |
| With extension | 51 (15.7) | |
| Current knee pain | 176 (54.3) | |
| Current ankle pain | 32 (9.9) | |
| Anterior tightness (HBD > 0 cm) | 223 (68.8) | |
| Posterior tightness (SRD < mean – 1 SD) | 145 (44.8) |
Training time data were missing for 18 participants
BMI Body mass index, HBD Heel-buttock distance, SD Standard deviation, SRD Sit-and-reach distance
Low back pain and thigh tightness
Associations between lower extremity tightness and LBP phenotypes showed that players with posterior thigh tightness had a significantly higher prevalence of current LBP (p < 0.05). They also had higher prevalences of lifetime LBP and LBP requiring rest while playing basketball (p < 0.05). In contrast, anterior thigh tightness was not significantly associated with LBP. LBP induced by lumbar flexion or extension was not significantly associated with either anterior or posterior thigh tightness. Players with current LBP at examination were significantly older, trained more days per week, had a higher BMI, and reported knee pain (all p < 0.05, Table 2). Similarly, players with lifetime LBP were significantly older, had longer basketball careers, had more fixed playing positions, trained more days per week, had a higher BMI, and reported knee pain (all p < 0.05, Table 2). Detailed univariate comparisons for LBP induced by lumbar flexion or extension are presented in Table 3.
Table 2.
Demographic characteristics and low back pain (LBP) status of the participants
| Current LBP | Lifetime LBP | LBP need for rest | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| + | - | p-value | + | - | p-value | + | - | p-value | |||
| Number | 15 (4.6) | 309 (95.4) | 64 (19.8) | 260 (80.2) | 29 (9.0) | 295 (91.0) | |||||
| Age (year) | 12.7 [1.3] | 11.0 [1.6] | 0.0002 | 12.0 [1.4] | 10.9 [1.6] | < 0.0001 | 12.4 [1.3] | 11.0 [1.6] | 0.0002 | ||
| School | Elementary school | 6 (12.3) | 257 (97.7) | 44 (68.8) | 219 (84.2) | 6 (12.3) | 257 (97.7) | ||||
| Junior high school | 9 (14.8) | 52 (85.3) | 0.0003 | 20 (31.2) | 41 (15.8) | 0.0045 | 9 (14.8) | 52 (85.3) | 0.0003 | ||
| Sex | Male | 4 (26.7) | 125 (40.4) | 25 (39.1) | 104 (40.0) | 10 (34.5) | 119 (40.3) | ||||
| Female | 11 (73.3) | 184 (59.6) | 0.2748 | 39 (60.9) | 156 (60.0) | 0.8908 | 19 (65.5) | 176 (59.7) | 0.5387 | ||
| Basketball career (year) | 3.3 [2.1] | 2.5 [1.6] | 0.1952 | 3.3 [1.9] | 2.4 [1.5] | 0.0012 | 3.4 [1.9] | 2.5 [1.6] | 0.019 | ||
| > 2 years | 8 (53.3) | 146 (47.2) | 0.6534 | 41 (64.1) | 113 (43.4) | 0.0034 | 18 (62.1) | 136 (48.3) | 0.1039 | ||
| Start age (year) | 9.4 [1.9] | 8.5 [1.8] | 0.0878 | 8.7 [1.9] | 8.5 [1.8] | 0.4894 | 9.0 [1.9] | 8.5 [1.8] | 0.1767 | ||
| < 8 | 6 (40.0) | 163 (52.8) | 0.2754 | 34 (53.1) | 135 (51.9) | 0.74 | 13 (44.8) | 156 (52.9) | 0.6667 | ||
| Position | Guard | 3 (20.0) | 57 (18.5) | 14 (21.9) | 46 (17.7) | 6 (20.7) | 54 (18.3) | ||||
| Forward | 2 (13.3) | 35 (11.3) | 12 (18.8) | 25 (9.6) | 5 (17.3) | 32 (10.9) | |||||
| Center | 4 (26.7) | 42 (13.6) | 13 (20.3) | 33 (12.7) | 8 (27.6) | 38 (12.9) | |||||
| Not fixed | 6 (40.0) | 175 (56.6) | 0.4753 | 25 (39.1) | 156 (60.0) | 0.0158 | 10 (34.5) | 171 (58.0) | 0.0537 | ||
| Training time (h) | 10.6 [3.6] | 9.7 [4.2] | 0.2504 | 10.3 [4.0] | 9.7 [4.2] | 0.1892 | 10.9 [4.4] | 9.7 [4.1] | 0.1203 | ||
| > 10 h | 6 (42.9) | 101 (34.6) | 0.514 | 22 (36.7) | 85 (34.3) | 0.7269 | 13 (44.8) | 94 (33.7) | 0.2306 | ||
| Training days | 5.0 [0.8] | 4.2 [1.2] | 0.0035 | 4.5 [1.1] | 4.1 [1.2] | 0.0089 | 4.8 [1.0] | 4.2 [1.2] | 0.0038 | ||
| > 4 days | 13 (86.7) | 148 (47.9) | 0.0034 | 40 (62.5) | 121 (46.5) | 0.0221 | 21 (72.4) | 140 (47.5) | 0.0103 | ||
| Height | 155.6 [8.6] | 145.1 [11.5] | 0.0003 | 150 [11.0] | 144.5 [11.5] | 0.0002 | 152.6 [11.8] | 144.9 [11.4] | 0.0004 | ||
| Low height (< Ave – 1 SD) | 1 (6.7) | 53 (17.2) | 14 (21.9) | 40 (15.4) | 4 (13.8) | 50 (17.0) | |||||
| Average | 11 (73.3) | 213 (68.9) | 41 (64.1) | 183 (70.4) | 20 (69.0) | 204 (69.2) | |||||
| High height (> Ave + 1 SD) | 3 (20.0) | 43 (13.9) | 0.5074 | 9 (14.1) | 37 (14.2) | 0.4690 | 5 (17.2) | 41 (13.9) | 0.8329 | ||
| BMI | 18.8 [2.8] | 17.2 [2.1] | 0.0233 | 17.8 [2.5] | 17.2 [2.1] | 0.0422 | 18.8 [2.8] | 17.2 [2.1] | 0.0343 | ||
| Overweight (BMI > 22) | 1 (6,7) | 19 (6.3) | 0.8636 | 3 (4.8) | 17 (6.6) | 0.7272 | 0 (0) | 20 (100) | 0.2909 | ||
| Underweight (BMI < 13.5) | 0 (0) | 3 (1.0) | 1 (1.6) | 2 (0.8) | 0 (0) | 3 (100) | |||||
| Current knee pain | 14 (93.3) | 162 (52.4) | 0.0006 | 48 (75.0) | 128 (49.2) | 0.0002 | 23 (79.3) | 153 (51.9) | 0.0046 | ||
| Current Ankle pain | 2 (13.3) | 30 (9.7) | 0.64 | 9 (14.1) | 23 (8.9) | 0.2102 | 3 (10.3) | 29 (9.8) | 0.9294 | ||
| Anterior tightness | 10 (66.7) | 213 (68.9) | 0.8532 | 45 (70.3) | 178 (68.5) | 0.7746 | 21 (72.4) | 202 (68.5) | 0.6621 | ||
| Posterior tightness | 11 (73.3) | 134 (43.4) | 0.026 | 42 (65.6) | 103 (39.6) | 0.0002 | 21 (72.4) | 124 (42.0) | 0.0017 | ||
P-values were calculated using the chi-squared test for categorical variables and the Wilcoxon rank-sum test for continuous variables
Table 3.
Demographic characteristics of participants with low back pain (LBP) with lumbar motion
| LBP with lumbar flexion | LBP with lumbar extension | ||||||
|---|---|---|---|---|---|---|---|
| + | - | p-value | + | - | p-value | ||
| Number | 13 (4.0) | 311 (96.0) | 51 (15.7) | 273 (84.3) | |||
| Age (year) | 11.7 [0.9] | 11.1 [1.6] | 0.1503 | 11.8 [1.3] | 11.0 [1.6] | 0.0002 | |
| School | Elementary school | 12 (92.3) | 251 (80.7) | 39 (76.5) | 224 (82.0) | ||
| Junior high school | 1 (7.7) | 60 (19.3) | 0.2945 | 12 (23.5) | 49 (18.0) | 0.3494 | |
| Sex | Male | 6 (46.1) | 123 (39.5) | 21 (41.2) | 108 (39.6) | ||
| Female | 7 (53.9) | 188 (60.5) | 0.6337 | 30 (58.8) | 165 (60.4) | 0.8287 | |
| Basketball career (year) | 3.6 [1.8] | 2.5 [1.6] | 0.0313 | 3.0 [1.7] | 2.5 [1.6] | 0.0363 | |
| > 2 years | 10 (76.9) | 144 (46.5) | 0.0312 | 29 (56.9) | 125 (46.0) | 0.1524 | |
| Start age (year) | 8.1 [1.3] | 8.6 [1.8] | 0.4299 | 8.8 [1.7] | 8.5 [1.8] | 0.2132 | |
| < 8 | 9 (69.2) | 160 (51.5) | 0.2711 | 26 (51.0) | 143 (52.4) | 0.6241 | |
| Position | Guard | 3 (23.1) | 57 (18.3) | 8 (15.7) | 52 (19.1) | ||
| Forward | 3 (23.1) | 34 (10.9) | 10 (19.6) | 27 (9.9) | |||
| Center | 0 (0) | 46 (14.8) | 11 (21.6) | 35 (12.8) | |||
| Not fixed | 7 (53.9) | 174 (56.0) | 0.2962 | 22 (43.1) | 159 (58.2) | 0.0484 | |
| Training time (h) | 9.7 [4.9] | 9.8 [4.2] | 0.7733 | 11.4 [4.4] | 9.5 [4.1] | 0.0034 | |
| > 10 h | 5 (38.5) | 102 (34.6) | 0.7734 | 25 (51.0) | 82 (31.7) | 0.0091 | |
| Training days | 3.7 [1.4] | 4.2 [1.2] | 0.1407 | 4.4 [1.1] | 4.2 [1.2] | 0.1522 | |
| > 4 days | 5 (38.5) | 156 (50.2) | 0.4085 | 29 (56.9) | 132 (48.4) | 0.2645 | |
| Height | 143.8 [10.7] | 145.6 [11.7] | 0.6667 | 150.1 [11.1] | 144.7 [11.5] | 0.0009 | |
| Low height (< Ave – 1 SD) | 7 (53.9) | 47 (15.1) | 9 (17.7) | 45 (16.5) | |||
| Average | 5 (38.5) | 219 (70.4) | 32 (62.8) | 192 (70.3) | |||
| High height (> Ave + 1 SD) | 1 (7.7) | 45 (14.5) | 0.0012 | 10 (19.6) | 36 (13.2) | 0.4403 | |
| BMI | 16.7 [2.6] | 17.3 [2.2] | 0.1381 | 17.8 [2.3] | 17.2 [2.2] | 0.0221 | |
| Overweight (BMI > 22) | 0 (0) | 20 (6.5) | 0.5917 | 1 (2.0) | 19 (7.6) | 0.2818 | |
| Underweight (BMI < 13.5) | 0 (0) | 3 (1.0) | 1 (2.0) | 2 (0.7) | |||
| Current knee pain | 8 (61.5) | 168 (54.0) | 0.5939 | 40 (78.4) | 136 (49.8) | 0.0002 | |
| Current Ankle pain | 3 (23.1) | 29 (9.3) | 0.1035 | 6 (11.8) | 26 (9.5) | 0.6255 | |
| Anterior tightness | 6 (46.2) | 217 (69.8) | 0.0716 | 36 (70.6) | 187 (68.5) | 0.7674 | |
| Posterior tightness | 7 (53.9) | 138 (44.4) | 0.501 | 27 (52.9) | 118 (43.2) | 0.2001 | |
P-values were calculated using the chi-squared test for categorical variables and the Wilcoxon rank-sum test for continuous variables
Association between low back pain and thigh tightness
Multivariable logistic regression analysis was performed to examine the relationship between thigh tightness and lifetime LBP (Table 4). The model was adjusted for school level, sex, training days per week, years of play, current knee pain, and BMI. The analysis showed that posterior thigh tightness was independently associated with lifetime LBP (odds ratio: 2.11; 95% confidence interval (CI): 1.07–4.15; p = 0.0304). Current knee pain was also independently associated with lifetime LBP (p = 0.0012) (Table 4). No significant interaction effects (e.g., sex × posterior thigh tightness and knee pain × posterior thigh tightness) were observed. To address potential temporal ordering biases, a sensitivity analysis was conducted after removing current knee pain from the multivariable model. The results remained consistent, with posterior thigh tightness maintaining a significant independent association with lifetime LBP (odds ratio: 2.01; 95% CI: 1.04–3.89; p = 0.0381).
Table 4.
Multivariable logistic regression analysis for factors associated with lifetime LBP
| Variables | Odds ratio | 95% CI | p-value |
|---|---|---|---|
| Posterior thigh tightness (Present vs. Absent) | 2.11 | 1.07–4.15 | 0.0304 |
| Anterior thigh tightness (Present vs. Absent) | 0.82 | 0.40–1.68 | 0.582 |
| School level (Junior high vs. Elementary) | 1.29 | 0.54–3.11 | 0.5653 |
| Sex (Female vs. Male) | 1.17 | 0.63–2.15 | 0.6223 |
| Years of play (continuous) | 1.18 | 0.98–1.42 | 0.0869 |
| Training days per week (continuous) | 1.06 | 0.77–1.47 | 0.7164 |
| Current knee pain (Present vs. Absent) | 3.09 | 1.56–6.12 | 0.0012 |
| Body mass index (continuous) | 1.11 | 0.95–1.29 | 0.1913 |
The primary variable of interest is highlighted in bold
LBP Low back pain, CI Confidence interval
Discussion
This study found that posterior thigh tightness was independently associated with lifetime LBP in adolescent basketball players. The prevalence of LBP in this study was comparable with that reported in a previous Japanese study [2]. Notably, approximately half of the athletes with LBP experienced symptoms severe enough to disrupt their ability to play basketball, indicating that a substantial portion developed more severe LBP.
A previous systematic review of sports-specific risk factors for LBP reported that reduced lumbar range of motion in flexion and extension, as well as anterior thigh tightness, were associated with LBP in athletes [13]. When examining the relationship between LBP and lower extremity tightness by sport and age group, quadriceps tightness was associated with LBP in young players [18]. An association between quadriceps tightness and LBP has also been reported in elementary school-aged softball players [19]. However, the relationship between hamstring tightness and LBP remains controversial, with studies supporting and refuting this association. A previous study demonstrated that limited straight leg raise (SLR) was associated with LBP in high school baseball players [21]. In contrast, a prospective cohort study of 86 adolescent athletes reported no association between limited SLR performance and LBP [25], and a cross-sectional study found no association between hamstring tightness and severe LBP [26]. Similarly, no association between lower extremity tightness and LBP was observed in female adolescent gymnasts [27]. However, the lack of association in these prior studies may reflect the inclusion of highly heterogeneous populations (such as general schoolchildren or mixed cohorts) [25, 26] or athletes characterized by hypermobility [27], which can obscure sport-specific mechanical risks. Hence, the relationship between LBP and lower-extremity tightness, particularly posterior thigh tightness, may depend on sport type, age, and assessment methods. For instance, the mechanical demands placed on the spine in multidirectional jumping sports like basketball differ fundamentally from those in asymmetric throwing sports or extreme flexibility sports. The present study identified a significant association between posterior thigh tightness and LBP in young basketball players aged 7–14 years. suggesting that this vulnerability may be a distinct characteristic of this specific population, likely driven by the combination of growth-related flexibility deficits and the repetitive mechanical stress of basketball.
Regarding the relationship between LBP and the lower extremities, thigh flexibility and pelvic movement may represent underlying mechanisms [16, 17]. However, it is important to acknowledge that no kinematic data were collected in our study; hence, this biomechanical explanation serves as a theoretical framework rather than a demonstrated pathway. Posterior thigh tightness is associated with restricted pelvic anteversion, which could contribute to the development of LBP [16]. Limited pelvic anteversion may increase stress on the anterior column of the lumbar spine, including the intervertebral discs, leading to LBP [15, 17]. Another study identified insufficient hamstring extensibility as an important risk factor for LBP in basketball and soccer players and reported a particularly strong association in male athletes [17]. Similarly, pelvic posterior tilt may be limited by anterior thigh and iliopsoas tightness, resulting in compensatory lumbar hyperextension and pain during lumbar extension [18, 19]. Conversely, anterior thigh tightness may restrict lumbar extension, which could represent one of the pathomechanisms underlying anterior thigh tightness and pain with lumbar extension [18, 19]. Interestingly, posterior tightness was associated with cumulative lifetime LBP but not with acutely provoked LBP during the examination. This is likely because acute provocation only captures currently symptomatic players, whereas lifetime LBP reflects a broader history of mechanical stress. Furthermore, players with previous LBP may have developed movement adaptations to avoid acute pain during examination. Additionally, the small number of players presenting with flexion-provoked LBP (n = 13) may have limited the statistical power to detect a significant association. Regarding covariates, current knee pain was also strongly associated with LBP. Knee pain in young athletes may reflect a broader musculoskeletal vulnerability profile—such as periods of rapid growth or poor movement mechanics—rather than acting solely as a localized confounder.
In contrast to previous studies on youth baseball and softball players [18, 19], anterior thigh tightness was not significantly associated with LBP in our cohort of young basketball players. This discrepancy may be attributed to sport-specific biomechanics. Throwing motions require dynamic trunk extension, where anterior thigh tightness can directly restrict pelvic posterior tilt and cause compensatory lumbar hyperextension, leading to LBP. However, in basketball, the repetitive impact of jumping and landing may rely more heavily on the shock-absorbing capacity of the hamstrings and pelvic anteversion.
Regarding the severity of symptoms, approximately half of the athletes with a history of LBP in this study experienced pain severe enough to disrupt their ability to play basketball. Although this relatively high proportion of severe cases may reflect the actual severity of LBP caused by the intense mechanical demands of basketball, it could also be partially influenced by the episodic nature of youth LBP and recall bias, as transient or mild pain is easily forgotten, whereas episodes requiring rest are more readily remembered.
Although previous studies have investigated the relationship between lower-extremity tightness, pelvic mobility, and LBP [28–33], it remains unclear whether hamstring tightness is a cause or a consequence of LBP. While the odds ratio of 2.11 suggests that the association may be clinically relevant, we acknowledge that causality and temporality cannot be inferred from this cross-sectional study. Furthermore, the relatively wide confidence interval suggests that posterior thigh tightness is likely one of several contributing factors. Therefore, it should be viewed as a useful marker for screening rather than an isolated cause. Flexibility may serve as an indicator warranting further investigation; however, prospective studies are needed to clarify the causal relationship between LBP and posterior thigh tightness.
This study has some limitations. First, given its cross-sectional design, causal relationships between LBP and hamstring tightness could not be established, and reverse causation cannot be excluded; therefore, longitudinal studies are required. Second, since the history of LBP was assessed using a self-reported questionnaire, the results may be subject to recall bias. Third, no imaging studies were performed to identify the underlying causes of LBP. Magnetic resonance imaging may be useful in future studies, particularly for differentiating conditions such as spondylolysis. Fourth, the data utilized in this study were collected between 2013 and 2014. Although the fundamental relationship between flexibility and LBP is unlikely to have changed, training methods and awareness of LBP in young athletes may have evolved since then. Fifth, limitations exist regarding the criteria used to define muscle tightness. Posterior thigh tightness was assessed using the SR test, which also reflects trunk mobility. Although the SLR test may evaluate hamstring length more directly than the SR test, SLR presents methodological challenges in mass screenings, such as handling laterality and lacking established age-adjusted normative values. Conversely, defining tightness via the SR test (below mean − 1 SD) allowed us to precisely adjust for natural developmental variations using a nationwide dataset, providing an objective evaluation of true flexibility deficits in this growing population. For anterior thigh tightness, an HBD cutoff of 0 cm was used, resulting in approximately 70% of participants being classified as having tightness. The use of alternative cutoff values may have influenced the findings. Sixth, excluding participants who missed the physical examination could potentially introduce selection bias; however, because these exclusions were primarily attributable to logistical scheduling constraints rather than health status, we consider this systematic bias to be minimal. Finally, we did not assess psychosocial variables (e.g., sleep, stress, or fear of movement) or pubertal maturation status, which are known to influence musculoskeletal pain in the 7–14 year age group.
Despite these limitations, this study has several strengths, including a relatively large sample size and a specific focus on young basketball players, which enabled a detailed multivariable analysis of sport-specific physical characteristics while adjusting for relevant confounders. Building on these findings, we plan to conduct a longitudinal study to clarify the temporal and causal relationships between posterior thigh tightness and LBP.
Conclusions
We found that posterior thigh tightness was independently associated with lifetime LBP in young basketball players. Future longitudinal studies are needed to determine temporality and causality between posterior thigh tightness and LBP.
Supplementary Information
Additional file 1. English translation of the Japanese questionnaire used in this study
Additional file 2. Age-stratified normative values for sit-and-reach distance obtained from the 2014 Annual Physical Fitness and Motor Ability Survey
Additional file 3. Nationwide survey data on height by sex and age group in Japan (2014)
Additional file 4. Comparison of demographic characteristics and LBP history between included and excluded players
Acknowledgements
The authors gratefully acknowledge the Fukushima Physical Therapy Association Medical Support Team for their collaboration and assistance with this study. The authors would like to thank Editage (https://www.editage.jp) for English language editing.
Abbreviations
- LBP
Low back pain
- HBD
Heel—buttock distance
- SR
Sit—and—reach
- SLR
Straight leg raise
- BMI
Body mass index
- SD
Standard deviation
- OR
Odds ratio
Authors’ contributions
KW: Conceptualization, Methodology, Investigation, Data curation, Formal analysis, Writing—original draft.KO, KT, TS, YK: Investigation, Data curation, Formal analysis, Writing—review & editing.TK: Formal analysis (statistics), Writing—review & editing.HK, KK, MH, TN: Conceptualization, Methodology, Writing—review & editing.YM: Conceptualization, Methodology, Supervision, Project administration, Writing—review & editing.All authors read and approved the final manuscript.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study was approved by the Ethics Committee of Fukushima Medical University (approval number: 2160). Written informed consent to participate in the study was obtained from all participants and their guardians.
Consent for publication
No individual data is being published as part of this manuscript.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Additional file 1. English translation of the Japanese questionnaire used in this study
Additional file 2. Age-stratified normative values for sit-and-reach distance obtained from the 2014 Annual Physical Fitness and Motor Ability Survey
Additional file 3. Nationwide survey data on height by sex and age group in Japan (2014)
Additional file 4. Comparison of demographic characteristics and LBP history between included and excluded players
Data Availability Statement
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.