Background: The impact of instability resistance training (IRT) on the biomechanical properties and muscle activation patterns of persons with different arch heights is not well researched, despite its popularity in the domains of sports and rehabilitation. The purpose of this study was to investigate the effects of IRT on the lower limb biomechanics, muscle activation patterns, and motor control abilities of individuals with different arch heights and to provide scientific evidence for personalized exercise training and rehabilitation strategies.

Methods: Sixty-six healthy adult male subjects were selected and categorized into three groups based on their arch height. They performed Bulgarian squats on an unstable surface. The kinematics data obtained from the Vicon system were imported into an OpenSim musculoskeletal model and analyzed using SPM1D one-way ANOVA. The electrical data collected from the electromyographic (EMG) device was utilized for EMGworks Analysis, which involves processing and calculating integrated EMG (IEMG) and root mean square (RMS) contributions, as well as analyzing muscle activation. SPSS was used to perform one-way ANOVA.

Results: Ankle inversion and eversion showed significant differences between individuals with low arches and those with high arches (0%-16% phase, p < 0.001; 66%-95% phase, p < 0.001) as well as those with normal arches (81%-89% phase, p = 0.011). The gastrocnemius medial (GL) RMS was found to be considerably lower in individuals with high arches compared to those with low arches (p = 0.040) and normal arches (p < 0.001). The IEMG of the rectus femoris (RF) muscle was considerably reduced in individuals with high arches compared to those with low arches (p = 0.007) and normal arches (p = 0.014).

Conclusions: Individuals with high arches encounter higher joint strain and reduced muscular engagement while performing IRT activities. Customized exercise that targets specific muscle groups, in conjunction with IRT, enhances joint stability. Individuals with low arches may experience decreased foot stability and muscle fatigue during intense physical activity, such as IRT. These individuals can benefit from improved foot support. This method enhances muscle coordination and modulation, hence improving sports performance and providing helpful exercise suggestions to prevent injuries in the general population.