Running is a full body movement that requires the feet to support the body and absorb forces greater than the individual's body weight in a repeated fashion. If the musculoskeletal structures of the feet cannot withstand and disperse the force applied, injury and dysfunction will occur. Without the inherent support of the foot musculature, ligaments are strained, and bones of the foot and ankle must absorb all forces, directly. When the medial longitudinal arch cannot be supported, the entire structure collapses, causing the foot to pronate. These postural signs indicate pes planus, or flat feet. Custom foot orthoses (CFOs) are commonly used to manage pes planus and research within the last 25 years has not provided clear insight on how CFOs influence running mechanics of joints and segments proximal to the foot (knee and hip). Additionally, CFO intervention has not been compared to exercise programming that focuses on strengthening the muscles that provide the foot with intrinsic strength. This study will provide insight on how these two interventions may influence foot biomechanics in the pes planus foot. We are hopeful that our findings can help to inform rehabilitation professionals in how different interventions can alter biomechanical outcomes related to pes planus. Previous literature also commonly focuses on an aging or sedentary individuals, while this study will focus on young active participants with a pes planus foot type.

Healthy recreational runners between the ages of 18-35 years old with pes planus will be recruited to participate. Participants will be randomly appointed to one of two groups: 1) the CFO group will wear CFOs for 8 weeks; and 2) the exercise group will be assigned an exercise protocol to complete each day for eight weeks. Participation will consist of completion of a prolonged run protocol in two testing sessions, pre- and post-intervention, and compliance to their assigned intervention. Three-dimensional kinematic data will be collected using a 10-camera motion capture system (Qualisys). For each data collection session, passive reflective markers will be placed on the participant both lower extremities, and participants will be instrumented with a heart rate (HR) monitor. The prolonged run protocol will consist of a five-minute warm-up phase, where participants will choose a comfortable running speed, with a desired HR at approximately 120 beats per minute (bpm). After the warm-up, participants will be permitted to stretch if desired, as they would before a typical run. Once ready, the participant will select a comfortable running pace that best represents their typical training pace. Running speed will be intermittently increased. A member of the research team will monitor the participant throughout the trial to check their HR, ask them to rate their perceived exertion on Borg's RPE scale (which will be displayed in front of them), and ask them to rate any pain they may be feeling on a scale from 1-10. The prolonged run protocol will end when any of the following occurs: 1) participant HR reaches 85% of their HR max, 2) participant rates the activity a score of 17 (very hard) on Borg's RPE Scale, or 3) the participant gives a 7/10 pain rating. Once the protocol has ended, participants will enter a cool-down phase where they will jog or walk until HR lowers. Participants will be able to stretch again following the protocol if desired.