46 Chapter 3 ABSTRACT Objectives: To establish normative values for calf muscle strength-endurance, adjusted for personal characteristics Methods: 500 individuals without current or previous symptoms of Achilles tendinopathy or recent lower limb immobilization were included. The primary outcome measures were the number of repetitions, total work (J), total vertical displacement (cm) and peak height (cm) upon the single-leg Heel Rise Endurance Test (HRET), assessed using the validated Calf Raise Application. A multiple quantile regression model was developed, incorporating covariates (personal characteristics) previously identified to significantly impact HRET metrics. Median (50.0th percentile) and 95% reference intervals (2.5th-97.5th percentiles) were derived. Results: Of the 500 participants included, 55% were female and the majority (88%) participated in sports and 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 9.3/9.6cm. There was no significant difference between the dominant and non-dominant leg for any of the HRET metrics. Lower physical activity levels, female gender, and higher body mass index (BMI) were associated with lower HRET metrics. Conclusions: Outcomes of the HRET are influenced by personal characteristics, with female gender, higher BMI, and lower physical activity levels being associated with lower HRET metrics. We have developed an openly accessible calculator for estimating normative HRET metrics (www.achillestendontool.com/HRET). This can be a valuable tool for healthcare providers to monitor personalized trajectories of recovery and provide well-informed rehabilitation guidance. Documenting more than the number of repetitions is important when assessing calf muscle function using the HRET.
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