The aim is to compare the effects of intrinsic foot muscles and tibialis posterior strengthening exercise, and customized arch support insoles on foot posture, plantar force distribution, and balance in individuals with flexible pes planus.

The aim is to compare the effects of intrinsic foot muscles and tibialis posterior strengthening exercise, and customized arch support insoles on foot posture, plantar force distribution, and balance in individuals with flexible pes planus. Forty-two individuals with flexible pes planus will be recruited into the study according to the inclusion criteria. Participants will be randomly divided into three groups: (1) Exercise, (2) Insole, (3) Exercise plus Insole. Exercises will be performed three times per week for six weeks, also custom-made insoles will be worn for six weeks. Foot posture will be assessed using the Navicular drop, Valgus index and Foot posture index-6. Plantar force variables will be recorded by the pressure-sensitive mat (HR Mat, Tekscan, USA) mounted in the middle of the 6-meter walkway in three sessions: (1) Upright standing, (2) Walking at different speeds: self-selected slow, normal and fast speeds, (3) Walking just after the heel-rise test for endurance. Balance performance will be assessed by the Balance Master System (NeuroCom® International Inc., USA). The assessments will be made pre/post intervention and at 6-weeks follow-up.

Inclusion Criteria:

1. being between 18 and 40 years of age,
2. having Navicular drop test greater than 10 mm,
3. having Foot posture index-6 greater than or equal to 6,
4. having bilateral flexible pes planus.

Exclusion Criteria:

1. a lack of anatomical integrity of the foot,
2. a history of surgery or trauma in the foot region,
3. other musculoskeletal or neurological problems which may affect balance and gait performance.
4. having received any treatment for lower extremity disorders including pes planus within the last 1 year
5. having a body mass index equal to or greater than 30.