Letter to the Editor concerning ‘The Calf Raise App shows good concurrent validity compared with a linear encoder in measuring total concentric work’: Let's not compare apples to oranges

Abstract

The authors state that this study was designed as a validity study, yet it appears to be an add‐on to another prospectively registered study (NCT05323773) with no initial intention of concurrent validation of the Calf Raise App. To properly assess the validity of the systems, similar reference points (e.g., the lateral side of the foot) should be used, and outcomes should be compared to a gold standard, such as 3D motion analysis.