Reliability of direct and indirect measures of intrinsic foot muscle strength in adults: A systematic review

Background: The aim of this systematic review was to summarize the existing literature on evaluation methods developed to measure intrinsic foot muscle strength in both symptomatic and asymptomatic individuals. The specific objectives was to provide an overview of the evaluation methods with their protocols and reliability.

Methods: Five databases (PubMed, Embase, Web of Science, Cochrane Library and SPORTDiscus) were searched up to August 2023. Studies reporting direct or indirect measures of intrinsic foot muscle evaluation with no limitation to sex, BMI or ethnicity were included. The inclusion criteria were applied systematically, and the methodological quality of the selected articles was assessed using The Downs and Black Checklist.

Findings: Sixteen studies provided results of direct measures of intrinsic foot muscle strength, while indirect measures were reported in 19 articles. Direct measurement methods such as dynamometry (ICC 0.75-0.99) and plantar pressure (ICC 0.75-0.95) show high reliability. Among the indirect methods, both MRI (ICC 0.99) and ultrasound showed mostly high (ICC 0.66-0.99) reliability values.

Interpretation: Direct methods like dynamometry and plantar pressure show excellent reliability, but validity is uncertain. MRI is considered gold standard among indirect measurement techniques. However, portable ultrasound devices have gained popularity due to their strong agreement with MRI.