Purpose The purpose of this study was to investigate the relationship between joint flexibility and skeletal muscle morphology in adolescent soccer players. Methods We recruited 67 soccer players. Joint flexibility was assessed by heel buttock distance (HBD), straight leg raise (SLR), and sit-and-reach test (SAR). Muscle hardness, muscle thickness (MT), muscle cross-sectional area (CSA), and echo intensity were measured. These data were analyzed using the following classification methods: evaluation by chronological age and classification of predicted peak height velocity (PHV). A one-way ANOVA was conducted for each classification, and the Tukey method was used for post hoc tests. The Pearson correlation test was used to assess the relationship between joint flexibility and skeletal muscle outcomes. Results The reliability of each variable showed almost perfect (ICC 0.93–0.99). The results of classification by chronological age showed no significant differences in joint flexibility and skeletal muscle outcomes, while the results of classification by predicted PHV showed significantly lower values for early PHV compared to late PHV and post-PHV in HBD (p = 0.04, d = 0.72, 95% CI [ −6.96, −0.01]; p = 0.01, d = 1.01, 95% CI [ −8.01, −0.74]). In the SAR test, early and late PHV showed significantly lower values compared to post-PHV (p < 0.01, d = 1.13, 95% CI [ −16.08, −2.76]; p < 0.01, d = 0.96, 95% CI [ −13.77, −2.29]). In addition, MT and CSA, post-PHV showed gradually higher values compared to early PHV (p < 0.01, d = 1.17, 95% CI [ −0.52, −0.01]; p = 0.01, d = 0.98, 95% CI [ −1.88, −0.21]). Across all participants in the study, no significant associations were found between joint flexibility and muscle hardness. Conclusions The results of this study suggest that the biological maturity status (predicted PHV) provides a more sensitive discriminator of flexibility changes than chronological age in adolescent soccer players. This information is directly useful for coaches and adolescent athletes. Although we assessed muscle hardness using strain-ratio elastography and found no association with joint flexibility, further longitudinal and interventional studies using quantitative methods such as shear-wave elastography are needed to clarify the role of muscle stiffness in PHV-related changes in joint flexibility.

Reduced joint flexibility is not associated with skeletal muscle properties in adolescent soccer players

期刊论文
发表日期：

2026年3月3日

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Yuta Kosuge,
Takashi Yamashita,
Taisei Fujino,
Yudai Gonda,
Takahiro Inoue,
Hiroaki Seto,
Eisuke Ochi

摘要

Purpose

The purpose of this study was to investigate the relationship between joint flexibility and skeletal muscle morphology in adolescent soccer players.

Methods

We recruited 67 soccer players. Joint flexibility was assessed by heel buttock distance (HBD), straight leg raise (SLR), and sit-and-reach test (SAR). Muscle hardness, muscle thickness (MT), muscle cross-sectional area (CSA), and echo intensity were measured. These data were analyzed using the following classification methods: evaluation by chronological age and classification of predicted peak height velocity (PHV). A one-way ANOVA was conducted for each classification, and the Tukey method was used for post hoc tests. The Pearson correlation test was used to assess the relationship between joint flexibility and skeletal muscle outcomes.

Results

The reliability of each variable showed almost perfect (ICC 0.93–0.99). The results of classification by chronological age showed no significant differences in joint flexibility and skeletal muscle outcomes, while the results of classification by predicted PHV showed significantly lower values for early PHV compared to late PHV and post-PHV in HBD (p = 0.04, d = 0.72, 95% CI [ −6.96, −0.01]; p = 0.01, d = 1.01, 95% CI [ −8.01, −0.74]). In the SAR test, early and late PHV showed significantly lower values compared to post-PHV (p < 0.01, d = 1.13, 95% CI [ −16.08, −2.76]; p < 0.01, d = 0.96, 95% CI [ −13.77, −2.29]). In addition, MT and CSA, post-PHV showed gradually higher values compared to early PHV (p < 0.01, d = 1.17, 95% CI [ −0.52, −0.01]; p = 0.01, d = 0.98, 95% CI [ −1.88, −0.21]). Across all participants in the study, no significant associations were found between joint flexibility and muscle hardness.

Conclusions

The results of this study suggest that the biological maturity status (predicted PHV) provides a more sensitive discriminator of flexibility changes than chronological age in adolescent soccer players. This information is directly useful for coaches and adolescent athletes. Although we assessed muscle hardness using strain-ratio elastography and found no association with joint flexibility, further longitudinal and interventional studies using quantitative methods such as shear-wave elastography are needed to clarify the role of muscle stiffness in PHV-related changes in joint flexibility.