Reference Equations and Normative Data for Isometric Quadriceps and Handgrip Muscles STrength in Southern European Populations - RESTart: a Multicentre Study

The RESTart study (Reference equations and normative data for isometric quadriceps and handgrip STrength in Southern European populations) is a multicentre observational cross-sectional study conducted in Spain, Portugal and Italy. Peripheral muscle dysfunction, particularly reduced quadriceps muscle strength and handgrip, is common in people with chronic respiratory diseases and is associated with impaired physical function, hospitalisation and mortality. Accurate interpretation of muscle strength measurements requires population-specific reference equations and normative values. However, currently available reference data may not adequately represent Southern European populations. The primary objective of the study is to develop reference equations and normative values for isometric quadriceps muscle strength and handgrip in healthy adults aged 18-89 years. A secondary objective is to validate/assess clinical application of these reference data in people with chronic respiratory diseases, including chronic obstructive pulmonary disease, interstitial lung disease, asthma, bronchiectasis and cystic fibrosis. Healthy participants will be recruited from community settings using proportional stratification according to age, sex and country. Participants with chronic respiratory diseases will be recruited from collaborating clinical centres. Primary outcomes are isometric quadriceps muscle strength and handgrip assessed using standardised dynamometry protocols. Secondary outcomes include functional capacity, mobility and balance, symptoms, physical activity, health-related quality of life, and anthropometric variables; lung function and laboratory parameters only when available from medical records. The study is expected to provide robust reference equations and normative values for Southern European populations, supporting improved identification and monitoring of peripheral muscle dysfunction in both clinical practice and research.