T42 (classification)  T42 is a disability sport classification for disability athletics (track and jump events only), applying to athletes with single above the knee amputations or a disability that is comparable. This class includes ISOD classified A2 and A9 competitors. This classification is for disability athletics competing in track and jump events. This classification is one of several classifications for athletes with ambulant related disabilities. Similar classifications are T43, T44, T45 and T46. The International Paralympic Committee defined this class in 2011 as: "Single above knee amputees and athletes with other impairments that are comparable to a single above knee amputation. This includes athletes with loss of muscle power in the lower limbs consistent with Class F57 or F58 class." The International Paralympic Committee defined the T42 to T44 classifications on their website in July 2016 as, "Lower limb affected by limb deficiency, leg length difference, impaired muscle power or impaired range of movement". People who are amputees compete in this class, including ISOD A2 and A9. This class includes ISOD A2 classified athletes. People in this class use a prosthetic limb when competing in athletics. It has four parts: a socket, a knee, a shank and a foot. Above the knee amputees have difficulty using standard able-bodied spint actions because of the differences in their functional muscle mass. As a result, they often use a specialized sprinting technique called “Leg-Over-Leg”. This technique involves using hip extensions to avoid deceleration caused by the prosthetic leg hitting the ground. Use of a specially made carbon fibre running prosthetic leg assists runners in this class in lowering their heart rate compared to using a prosthetic not designed for running. Runners in this class can have lower metabolic costs compared to elite runners over middle and long distances. A study was done comparing the performance of athletics competitors at the 1984 Summer Paralympics. It found there was no significant difference in performance in times between women in A1, A2 and A3 in the 100 meter race, men in A1, A2 and A3 in the 100 meter race, and men in A1, A2, A3 and A4 in the 400 meter race. Members of the ISOD A9 class compete in T42, T43, T44, F42, F43, F44, F56, F57, and F58. The shank length of people in this class can differ dramatically, and is not uniform across the class.