Cold-weather warfare
Trench foot is a medical condition caused by prolonged exposure of the feet to damp, unsanitary, and cold conditions at temperatures as warm as for as few as 13 hours. Exposure to these environmental conditions causes deterioration and destruction of the capillaries and leads to morbidity of the surrounding flesh. Affected feet may become numb, affected by erythema (turning red) or cyanosis (turning blue) as a result of poor blood supply, and may begin emanating a decaying odour if the early stages of necrosis (tissue death) set in. As the condition worsens, feet may also begin to swell. Advanced trench foot often involves blisters and open sores, which lead to fungal infections. If left untreated, trench foot usually results in gangrene, which may require amputation. If trench foot is treated properly, complete recovery is normal, though it is marked by severe short-term pain when feeling returns. Trench foot affected tens of thousands of soldiers engaged in trench warfare in World War I. Keeping feet warm and dry, or at least changing into warm and dry replacement footgear, is the best way to avoid trench foot.
Barefoot running
The running shoe itself has also been examined as a possible cause of many injuries associated with shod running. One 1991 study found that wearers of expensive running shoes that are promoted as having special features, such as added cushioning or "pronation correction", were injured significantly more frequently than runners wearing inexpensive shoes. It has also been found that running in conventional running shoes increases stress on the knee joints up to 38%, although it is still unclear if this leads to a higher rate of heel injuries or not. One study suggests that there is no evidence that cushioning or pronation control in shoes reduces injury rates or reduces performance. It was also found that the belief that one's shoes have increased cushioning had no effect on increasing or decreasing ground reaction forces during walking. Modern running shoes can also increase joint torque at the hip, knee, and ankle, and the authors of the study even suggest that running in high heels might be better than modern running shoes. Improperly fitting shoes may also result in injuries such as a subungual hematoma – a collection of blood underneath the toenail. This may also be known as "runner's toe" or "tennis toe". However, a recent randomized controlled trial (RCT) suggested that heavier runners might be at an increased risk for injury in minimalist shoes (designed to mimic barefoot running) as compared to conventional footwear.