Correlation Between Soft Tissue Displacement and Functional Performance in Orthopedic Patients

The goal of this clinical trial is to investigate the correlations between dynamic soft tissue displacement, mechanical properties, and functional recovery across three studies: biceps femoris long head (BFlh) muscle injury, adult acquired flatfoot deformity (AAFD), and medial ulnar collateral ligament anterior bundle (mUCLAB) reconstruction. The main questions it aims to answer are:

1. In athletes with BFlh injury who have returned to sport but remain limited in full participation, does an 8-week Nordic hamstring exercise (NHE) program alter BFlh displacement measured by ultrasound speckle tracking (UST) during maximal eccentric testing and improve eccentric strength? 2. In adults with flexible AAFD/PCFD, does a 6-week intervention of conservative exercise and custom foot orthoses alter the dynamic mechanical behavior (longitudinal displacement and dynamic torsion tracked by UST) and mechanical properties (shear wave elastography, SWE) of the posterior tibial tendon (PTT)? 3. In overhead athletes after mUCLAB reconstruction, does an 8-week blood flow restriction (BFR) training program targeting the forearm flexor-pronator mass reduce regional strain quantified by UST and alter the Young's modulus of the reconstructed graft under dynamic valgus stress?

Researchers will compare biomechanical and functional outcomes within participants before and after each intervention, as well as against comparison groups (athletes with full return-to-sport clearance or asymptomatic flatfoot adults), using UST algorithms and SWE. Depending on their allocated cohort, participants will:

Part 1 (Hamstring Muscle Injury):

* Perform an 8-week progressive Nordic hamstring exercise (NHE) program (for the experimental group) * Undergo BFlh muscle stiffness assessment using SWE and power Doppler examination for intramuscular scar vascularity * Complete pain-free maximal isokinetic eccentric knee flexion tests and isometric contractions combined with UST and surface electromyography (sEMG) to measure muscle displacement, scar gap size, and peak torque * Complete hamstring flexibility testing (active knee extension test) and fill out the Functional Assessment Scale for Acute Hamstring Injuries (FASH)

Part 2 (adult acquired flatfoot deformity):

* Receive 6 weeks of conservative intervention consisting of wearing custom-molded foot orthoses (for at least 85% of days) combined with progressive PTT eccentric training, short-foot exercises, and calf stretches * Undergo SWE to evaluate proximal and distal PTT shear wave velocity. Perform progressive isometric foot adduction on an isokinetic dynamometer with UST recording raw radiofrequency (RF) data to measure PTT longitudinal displacement and cross-sectional dynamic torsion * Complete clinical assessments at baseline, 6 weeks, and 12-week follow-up, including single-leg heel-rise tests, isokinetic strength, ankle range of motion, force-plate balance tests, 5-minute walk tests, and self-reported questionnaires (FFI-R, MSK-HQ)

Part 3 (Elbow Ligament Reconstruction Cohort):

* Participate in an 8-week progressive isokinetic strength training program for the forearm flexor-pronator mass combined with blood flow restriction, alongside grip training * Undergo dynamic elbow valgus stress testing at 5 N·m torque on an isokinetic dynamometer synchronized with UST and SWE to evaluate regional strain and Young's modulus of the reconstructed mUCLAB * Complete upper-extremity evaluations before and after training, including shoulder-elbow range of motion, isometric muscle strength using hand-held dynamometry, countermovement push-up (CMPU) power tests on force plates, and the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire