To critically assess the literature focused on strength training of the intrinsic foot muscles (IFM) and resulting improvements in foot function.
A search of electronic databases PubMed, CINHAL, Scopus, and SPORT Discus was completed between January 2000 to March 2022.
Randomized control trials (RCTs) with an outcome of interest with at least two weeks of IFM exercise intervention were included. Outcomes of interest were broadly divided in to five categories of foot posture (navicular drop (ND) and Foot Posture Index (FPI)), balance, strength, patient-reported outcomes (PROs), sensory function, and motor performance. The PEDro scale was used to assess the methodological quality of included studies with two independent reviewers rating each study. Studies with a PEDro score greater than 4/10 were included.
Data from the included studies were extracted by two independent reviewers. These data included design, participant characteristics, inclusion and exclusion criteria, type of intervention, outcomes, and the primary results. Random effects meta-analysis was performed to analyze difference between intervention and control groups for each outcome when there were at least two studies. Standardized mean differences (SMD) describe effect size with a 95% confidence interval (SMD range). When the confidence interval crossed zero the effect was not significant.
Thirteen studies were included and IFM exercise interventions were associated with decreasing ND (SMD range=0.37,1.83), and FPI (SMD range=1.03,1.69), improving balance (SMD range=0.18,1.86), strength (SMD range=0.06,1.52) and PROs for disability (SMD range=0.12,1.00) with pooled effect sizes favoring IFM intervention over control. There was no superiority of IFM exercises (SMD range=− 0.15,0.66) seen in reducing pain. We could not perform meta-analysis for sensory function and motor performance as there was only study reporting each outcome, however, these results supported the use of IFM strength training.
IFM strength training is helpful for patients in improving foot and ankle outcomes