Test-Retest Reliability of Soft Tissue Vibration Variables Across an Outdoor 5-km Run

The purpose of this study was to determine the test-retest reliability of soft tissue vibration (STV) measurements taken superficial to the medial gastrocnemius during a 5-km outdoor run. Twenty-eight trained athlete participants (female: n = 14 and male: n = 14) wore a triaxial inertial measurement unit mounted on the skin superficial to their medial gastrocnemius (500 Hz) and performed two 5-km outdoor runs on different days at a controlled, individualized pace. STV outcome measures-peak acceleration, damping coefficient, settling time, peak and median frequency, and power-were analyzed using a continuous wavelet transform from averaged running strides within the entire run and among three 1500-m segments from each testing session. Intraclass correlation coefficients reinforced good to excellent between-day reliability measures (.75-.92) for all STV outcome measures except peak frequency (.50) and moderate to excellent reliability when comparing days across the 3 segments of the run (.70-.94), except for peak frequency (.44-.57). No significant day × time interactions were observed (P = .06-.63). Overall, STV outcome measures assessed with an inertial measurement unit during outdoor running demonstrated good reliability, supporting methodologies to quantify STV in real-world settings with potential applications in running performance and injury prevention research.