Long-term training on sand changes lower limb muscle activities during running in runners with over-pronated feet

Running on sand could be a promising exercise intervention for the treatment of over-pronated feet. However, there is a lack of knowledge about the effects of running on sand on muscle activities. Therefore, this study aims to evaluate the long-term effects of running on sand on the activities of selected lower limb muscles in individuals with OPF compared with healthy controls.

Sixty recreational adult male runners with over-pronated feet (foot posture index > 10) were divided into two equal groups (intervention and control). Participants ran barefoot at a pre-defined speed (⁓3.3 m/s) over level stable ground both before and after long-term training on the sand. Muscle activities were recorded using a surface bipolar electromyography system.

For the intervention group, we found a reduced foot posture index (p < 0.001; d = 2.00) and significant group-by-time interactions for gluteus medius activity during the mid-stance phase (p < 0.028; d = 0.59). Significantly higher gluteus medius activity (p = 0.028, d = 0.569) was found during the post-test. We also observed significant group-by-time interactions for medial gastrocnemius activity during the push-off phase (p < 0.041; d = 0.54). Significantly larger medial gastrocnemius activity (p = 0.041; d = 0.636) was found during the post-test compared to the pre-test.

Long-term running on sand resulted in reduced pronation, increased medial gastrocnemius activity, and improved frontal plane pelvic stability due to higher gluteus medius activity.

IRCT20191211045704N1. Registered 25 February 2020. Retrospectively registered.