The heel-rise work test overestimates the performed work with 21-25% after an Achilles tendon rupture

Purpose: The purpose of this study was to evaluate concurrent validity of the heel-rise work test performed with use of the heel as a surrogate for the center of body mass. Methods: The study was a validity study performed on a prospective cohort of consecutive patients. Forty-five patients were included in the study. The heel-rise work test estimates the total work performed by repeated heel-rises until fatigue. In this study, the heel-rise work was assessed by the linear encoder and a motion capture system simultaneously for validation. The linear encoder was attached to the patient’s heel and reflective marker was attached to the pelvis and heel. Student’s paired t-test, linear regression analysis and Bland Altman plots were used to estimate the measurement error of the linear encoder. Results: The heel-rise work test overestimated the total work with 21.0% on the injured leg and 24.7% on the non-injured leg. Student’s paired t-test showed no difference in measurement error between the limbs (n.s.). The linear regression analysis showed no difference in limb symmetry index between the two methods of heel-rise work estimation (a (slope) = 1.00, R = 0.94, p < 0.0001). Conclusion: The heel-rise work test performed using the heel as a surrogate for center of body mass overestimates the total work with 21.0–24.7% compared to a gold standard but was able to precisely detect the relative difference between the limbs. The heel marker can be considered a valid measurement device for assessing relative differences between the limbs. Clinical relevance: Clinical testing of injuries to the lower body using the heel-rise work test is valid when using the relative difference between the limbs. Level of evidence: I.