Ultrasound Muscle Biomarkers as Predictors of Isometric Quadriceps Muscle Strength and Handgrip in Healthy Adults: an Observational Study

Overview

This observational study aims to determine whether ultrasound-derived muscle biomarkers can predict isometric quadriceps muscle strength and handgrip in healthy adults aged 18-89 years. The main questions it aims to answer are: * Which ultrasound muscle characteristics are associated with isometric quadriceps muscle strength and handgrip? * Can ultrasound-derived biomarkers be used to develop predictive models of muscle strength in healthy adults? Participants will undergo: * Ultrasound assessment of the quadriceps and forearm flexor muscles; * Measurement of isometric quadriceps muscle strength and handgrip using standardized dynamometry protocols; * Assessment of functional capacity, mobility and balance; * Completion of questionnaires related to health status, physical activity, nutrition, fatigue and health-related quality of life. The study will also assess the reliability of ultrasound measurements and explore the relationship between ultrasound variables, muscle strength, physical function and health-related factors.

Peripheral muscle strength is an important determinant of physical function, independence and health outcomes. Reduced quadriceps muscle strength and handgrip have been associated with functional limitations, frailty, hospitalization and mortality. Although muscle ultrasound is increasingly used to assess muscle morphology and quality, its ability to predict muscle strength remains incompletely understood. The MUSCLE-US study is a monocentre observational study designed to investigate the relationship between ultrasound-derived muscle biomarkers and isometric quadriceps muscle strength and handgrip in healthy adults. Participants aged 18-89 years will be recruited from community settings and stratified by age and sex. Ultrasound assessments will be performed on the quadriceps and forearm flexor muscles using standardized acquisition procedures. First-order variables (e.g., muscle thickness, cross-sectional area, pennation angle, fascicle length), second-order texture features and higher-order ultrasound biomarkers will be extracted and analysed. Isometric quadriceps muscle strength and handgrip will be measured using standardized dynamometry protocols. Additional assessments will include functional capacity tests, mobility and balance measures, physical activity, nutritional status, fatigue, dyspnoea, health-related quality of life, lifestyle factors and comorbidity profiles. The primary objective is to identify ultrasound biomarkers associated with quadriceps muscle strength and handgrip, and to develop predictive models of muscle strength. Secondary objectives include assessment of ultrasound measurement reliability and exploration of relationships between ultrasound biomarkers, muscle strength, physical function and health-related characteristics. Recruitment, assessor training, ultrasound standardisation procedures and reliability analyses will be conducted during the initial phase of the project, followed by the main recruitment and data collection phase and subsequent statistical modelling and dissemination activities.