ITF Taekwon-do is a combat sport involving large number of kicks; it requires rapid and forceful kicking (Saulite 2010). One of the main tasks of the training process is to develop kicking speed both in attack and counterattack, where an athlete should react adequately and execute a purposeful element as fast as possible to overtake his opponent (Saulite 2009). Often an essential element of the training program is a control over athlete's progress in training process. Thus in the weightlifting training (weightlifting is still the most popular way of strength training) progress can be easily controlled by following the increase of weight in a certain number of repetitions of a task. Additional laboratory tests can provide useful information about an athlete’s progress, for instance, whether there is the maximal strength increase at the certain speed or at the certain point of the movement amplitude (Knipse 2008). Isometric exercise is a form of resistance training in which an athlete uses the muscles of the body to exert a force either against an immovable object or to hold the muscle in a fixed position for a set duration of time. In this type of exercise, the muscle is contracted but does not change length during the exertion of force. Additionally the joint most closely associated with the effort remains static throughout the exercise (Zhou 1996). Maximal force values can be found in literature sources for eccentric, isotonic and isometric modes (Linnamo 2006, Maietta Latessa 2007). However, there is a lack of data about relationship between muscles' contractile abilities in isometric and dynamic modes. Kicks are executed in a very short time – 0.2-0.4 s depending on qualification of an athlete (Saulite 2009). Muscle's ability to exert maximal effort also lasts about 0.2-0.4 s. The question to study is how much an effort increase speed influences kicking speed and time for maximal hip flexion and total kick execution time. In the present research relationship between effort increase in hip flexion and kicking speed and time were studied.