Author(s): INOSTROZA, M., PEÑAILILLO, L., NEGUIMAN-NAHUEL, G., RAMPIREZ-CAMPILLO, R., Institution: UNIVERSIDAD METROPOLITANA DE CIENCIAS DE LA EDUCACIÓN / UNIVERSIDAD ANDRES BELLO, Country: CHILE, Abstract-ID: 928

INTRODUCTION:
Between 1990 and 2022, the global prevalence of obesity in youth increased from 1.9% to 8.1% [1]. Obesity may change the muscle architecture, enhance the muscle function [2], and increase the Achilles tendon (AT) thickness and stiffness. These adaptations can produce an imbalance between muscle and tendon, increasing the injury risk in youth [3]. Biological maturation induces similar muscle and tendon adaptations. The study aims to investigate the interaction between biological maturation and obesity on the gastrocnemius medialis (GM) architecture and function, and the AT structure and mechanical properties
METHODS:
48 youth were divided into four groups: normal-weight (NW) pre-age-to-peak height velocity (APHV) (6F/6M; APHV: -2.54±0.92 years), NW post-APHV (6F/6M;APHV:2.14±0.97 years), youth with obesity (OB) pre-APHV (6F/6M;APHV: -2.37±1.03 years, and OB post-APHV (6F/6M;APHV:1.66±0.69 years). Assessment included: i) GM architecture (thickness, pennation angle, and fascicle length); II) Plantar flexors (PF) function (maximal isometric voluntary contraction [MIVC] and rate of force development [RFD]). III) AT structure (AT: tibia length [AT: TL] ratio) and AT cross-sectional area. IV) AT mechanical properties (stiffness, strain, and Young’s modulus). Holm-Bonferroni post-hoc test followed significant ANCOVA effects (time [APHV]×groups [obesity-non-obesity]), with effect size calculated (partial eta squared [η²ₚ]). Approved by the Ethics Committee (code:14-26022024)
RESULTS:
A time and group effect, was observed, with greater GM thickness (p<0.0001,η²ₚ=0.44;p<0.0001;η²ₚ=0.40), pennation angle (p=0.005;η²ₚ=0.17; p<0.0001,η²ₚ=0.30), and fascicle length (p<0.0001;η²ₚ=0.28;p=0.0008;η²ₚ=0.10) in post-APHV compared with pre-APHV, and in OB compared with NW, respectively. A time effect was observed with a greater PF MIVC (p<0.0001;η²ₚ= 0.53), RFD50 (p<0.0001;η²ₚ= 0.36), and RFD200 (p<0.0001;η²ₚ= 0.41) in the post-APHV vs. Pre-APHV groups. A group effect was evidenced by a greater AT: TL ratio (p=0.019;η²ₚ= 0.06) in the NW pre-APHV vs. OB pre-APHV group. A time effect was evidenced by a greater AT CSA (p= 0.008;η²ₚ= 0.11) in NW post-APHV vs. Pre-APHV group. A time (p=0.003;η²ₚ= 0.17) and group effect (p=0.01;η²ₚ= 0.07) were evidenced for AT stiffness. Time effect was observed with a greater AT stiffness in the post-APHV vs. Pre-APHV group, and the group effect in the OB pre-APHV vs. the NW pre-APHV group. A time (p=0.0001;η²ₚ= 0.28) was shown with a greater AT Young’s modulus in the post-APHV vs. Pre-APHV groups. An interaction effect (p=0.01;η²ₚ= 0.13) was shown with a lower strain for the OB post-APHV vs. other three groups
CONCLUSION:
Biological maturation and obesity drive changes in muscle architecture. Biological maturation enhances muscle function and increases AT thickness and Young’s modulus, while obesity is associated with a lower AT:TL ratio. Both factors promote greater tendon stiffness and lower strain, potentially altering tendon loading in youth with obesity