Normative values for calf muscle strength-endurance in the general population assessed with the Calf Raise Application: A large international cross-sectional study

Background: Calf muscle strength-endurance can be reliably assessed with the Heel Rise Endurance Test (HRET), but normative values are lacking. Objectives: To establish normative values for calf muscle strength-endurance, adjusted for personal characteristics. Methods: 500 individuals without current/previous symptoms of Achilles tendinopathy or recent lower limb immobilization were included. Primary outcome measures were the number of repetitions, total work (J), total vertical displacement (cm), and peak height (cm) upon the single-leg HRET, assessed using the validated Calf Raise Application. A multiple quantile regression model was developed, incorporating covariates (personal characteristics) which significantly impacted HRET metrics. Median (50.0th percentile) and 95 % reference intervals (2.5th-97.5th percentiles) were derived. Results: 55 % of the participants were female and 88 % participated in physical activities. Median (dominant/ non-dominant leg) number of repetitions was 25/24, total work was 1374/1325 J, vertical displacement was 192/186 cm, and peak height was 9.3/9.6 cm. There was no significant difference between the dominant and non-dominant leg for any HRET metric. Lower physical activity levels, female sex, and higher body mass index (BMI) were associated with lower HRET metrics. Conclusions: Normative calf muscle strength-endurance metrics (number of repetitions, total work, total displacement, and peak height) were developed. Personal characteristics influence HRET outcomes, with female sex, higher BMI, and lower physical activity levels being associated with lower HRET metrics. An openly accessible calculator for estimating normative HRET metrics was developed to help healthcare providers monitor personalized recovery trajectories and provide well-informed rehabilitation guidance. Documenting HRET metrics beyond repetition count may aid in assessing impairment severity and evaluating calf muscle function.