Flat Feet and Implications on Performance
Flat foot (pes planus) is a condition in which the arch of the foot collapses and comes in contact with the ground, causing excessive pronation. Individuals with flat feet tend to have impaired mechanics of the big toe and little to no Windlass mechanism, which is responsible for allowing the foot to flex during loading phases of gait, supinate, and then become rigid again for push off. This biomechanical default can lead to poor walking and running mechanics, leading to further injury up the chain. Excessive pronation of the foot can lead to internal rotation of the tibia, placing your knee in a weak and unstable position.
As the ankle stresses into further inversion and the arch rolls into pronation, a slight inward rotation is placed in the tibia and translates through the knee joint, hip joint, and lower back. The same can happen in reverse, causing you to pronate your foot. Results of a 2008 military study indicate moderate to severe flat feet are associated with anterior knee pain and intermittent low back pain.
Flexible flatfoot is due to excessive pronation or rolling inward during weight-bearing. The foot appears flatfooted while standing in a full weight bearing position, yet the arch appears as the person extends their big toe. This is not a true collapsed arch, as the the Windlass mechanism is still operational. Whether you have true pes planus or flexible flatfoot, improper foot position during movements like the squat, deadlift, and jumping and landing can lead to serious injury.
There are a few ways to alleviate this biomechanical default. First, you can try a foot orthotic to help raise the arch. Inserts can help to realign your foot and ankle into a neutral position, which may help with further realignment up the chain. These orthotics must be worn with shoe that has a solid heel counter and shank to hold it in place. Muscular training of the feet, while generally helpful, will usually not result in increased arch height in adults. The arch of the foot is created passively by plantar fascia. The muscles in the feet are very short and quick to fatigue. Plus, the arch of the foot is created passively by the plantar fascia.
To correct this positional fault when squatting or jumping, think about screwing your feet into the ground and shoving your knees out. This will shift your body weight to the outer surface of the feet, raise the arches, externally rotate the tibia, and tighten the cruciate ligaments inside the knee to create stability. This will help to better transmit force through the lower extremity while protecting your knees and low back.
Kosashvili Y, Fridman T, Backstein D, Safir O, Ziv Y. The correlation between pes planus and anterior knee or intermittent low back pain. Foot & Ankle International. September 2008;29(9):910-913.