Evidence for Intrinsic Foot Muscle Training in Improving Foot Function: A Systematic Review and Meta-Analysis

Objective: To critically assess the literature focused on strength training of the intrinsic foot muscles (IFMs) and resulting improvements in foot function. Data Sources: A search of electronic databases (PubMed, CINAHL, Scopus, and SPORTDiscus) was completed between January 2000 and March 2022. Study Selection: Randomized control trials with an outcome of interest and at least 2 weeks of IFM exercise intervention were included. Outcomes of interest were broadly divided into 5 categories of foot posture (navicular drop and Foot Posture Index), namely: balance, strength, patient-reported outcomes, sensory function, and motor performance. The PEDro scale was used to assess the methodologic quality of the included studies with 2 independent reviewers rating each study. Studies with a PEDro score greater than 4/10 were included. Data Extraction: Data extracted by 2 independent reviewers were design, participant characteristics, inclusion and exclusion criteria, type of intervention, outcomes, and primary results. We performed a random-effects meta-analysis to analy ze the difference between intervention and control groups for each outcome when at least 2 studies were available. Stan- dardized mean differences (SMDs) describe effect sizes with 95% CIs (SMD ranges). When the CI crossed zero, the effect was not significant. Data Synthesis: Thirteen studies were included, and IFM exercise interventions were associated with decreasing navicu- lar drop (SMD range = 0.37, 1.83) and Foot Posture Index (SMD range = 1.03, 1.69) and improving balance (SMD range = 0.18, 1.86), strength (SMD range = 0.06, 1.52), and patient- reported outcomes for disability (SMD range = 0.12, 1.00), with pooled effect sizes favoring the IFM intervention over the control. The IFM exercises were not superior (SMD range = -0.15, 0.66) for reducing pain. We could not perform a meta-analysis for sen- sory function and motor performance, as only 1 study was avail- able for each outcome; however, these results supported the use of IFM strength training. Conclusions: Strength training of the IFMs was helpful for patients in improving foot and ankle outcomes.