Effect of double- density foot orthoses on ground reaction forces and lower limb muscle activities during running in adults with and without pronated feet

Background: The analysis of ground reaction forces and muscle activities during walking or running can help clinicians decide on the usage of foot orthoses, particularly in individuals with pronated feet. Here, we aimed to investigate the effects of double- density foot orthoses on running kinetics and lower limb muscle activities in adults with and without pronated feet. Methods: Forty male adults with pronated feet (PF: n = 20, age = 25.4 ± 0.3 years, body-mass-index [BMI] = 23.3 ± 1.2 kg/m2) and without pronated feet (WPF: n = 20, age = 26.4 ± 1.0 years, BMI = 24.0 ± 0.7 kg/m2) volunteered to participate in this study. The study was registered with the Iranian Registry of Clinical Trials (IRCT20220129053865N1). Ground reaction forces (Fx, Fy, Fz) and lower limb muscle activities (e.g., m. gastrocnemius) were recorded using surface electromyography (EMGs) during running at a constant speed of 3.2 m/s over an 18-m walkway with an embedded force plate. EMGs were normalized to maximum voluntary isometric contractions. Results: Test-retest reliability for running speed data was excellent for PF and WPF groups and for the entire study cohort with intraclass correlation coefficients > 0.95. The 2-way ANOVA revealed lower peak Fz (p = 0.011; d = 1.226), lower time-to-peak for Fx (p = 0.023, d = 1.068), Fy (p = 0.025, d = 1.056), and Fz (p = 0.045, d = 0.931) during running with foot orthoses in PF individuals. During the loading phase, PF and WPF exhibited lower gastrocnemius (WPF: p = 0.005, d = 1.608; PF: p = 0.001, d = 2.430) and vastus medialis (WPF: p < 0.001, d = 2.532; PF: p < 0.001, d = 2.503) activity when running with foot orthoses. Conclusions: Although double- density foot orthoses resulted in some beneficial biomechanical effects such as lower muscle activation (e.g., m. vastus medialis) in individuals with PF, foot orthoses constructions need further modifications to achieve even better running mechanics to enhance performance and lower limbinjury occurrence. Trial registration: IRCT20220129053865N1 (Registration date 19/08/2024).