to lessen discomfort. Over several weeks, slightly more material is added to the orthosis to raise the arch. These small changes allow the foot structure to adjust gradually, as well as giving the patient time to acclimatize to the sensation of wearing orthoses. In some cases, surgery can provide lasting relief, and even create an arch where none existed before; it should be considered a last resort, as it is usually very time-consuming and costly. A minimally-invasive surgical intervention involving a small implant is also available. The implant is inserted into the sinus tarsi and prevents the calcaneus and talus from sliding relative to each other. This prevents the sinus tarsi from collapsing and thus prevents the external symptom of the fallen arch from occurring. Athletic performance The effects of flat feet fall under two categories, which are asymptomatic and symptomatic. Individuals with rigid flat feet tend to exhibit symptoms such as foot and knee tendinitis, and are recommended to consider surgical options when managing symptoms. Individuals with flexible flat generally exhibit asymptomatic effects in response to their flat feet. According to AAP news and journal gateway, being flexibly flat-footed does not impede athletic performance. It is generally assumed by running professionals (primarily including some physical trainers, podiatrists, and shoe manufacturers) that a person with flat feet tends to overpronate in the running form. However, some also assert that persons with flat feet may have an underpronating if they are not a neutral gait. With standard running shoes, these professionals claim, a person who overpronates in his or her running form may be more susceptible to shin splints, back problems, and tendonitis in the knee. Running in shoes with extra medial support or using special shoe inserts, orthoses, may help correct one's running form by reducing pronation and may reduce risk of injury. Military performance Studies analyzing the correlation between flat feet and physical injuries in soldiers have been inconclusive, but none suggest that flat feet are an impediment, at least in soldiers who reached the age of military recruitment without prior foot problems. A 2005 study of Royal Australian Air Force recruits that tracked the recruits over the course of their basic training found that neither flat feet nor high arched feet had any impact on physical capability, injury rates or bipedal aptitude. Although there have been results rendered from military trials that have shown those with flat feet