Abstarct: Objective: One of the most important factors in health and exercise is aerobic fitness, which can be affected by various factors. Physical abnormalities can be one of these factors. A cruciate ligament is one of the most common abnormalities in the lower limb that affects the knee joint. The present study investigated the relationship between cardiovascular endurance and lower extremity electromyographic activity in boys with a crossed knee. Methods: In this study, 20 boys aged 20-27 years with cruciate knee were examined and the electromyographic activity of anterior tibialis(TA) muscles, internal twins(GM), internal wide(VM), external wide(VL), right thigh(RF), biceps(BF), semi-chin(ST) and middle serine muscle(GUT M) and cardiac endurance Vascular was measured. The correlation between muscle activity in three phases (primary, middle and pushing) and cardiovascular endurance was examined. Results and conlusion: The results showed that the correlation between hemisphere muscle and maximal oxygen consumption during the loading response phase is significant. However, in the present study, no significant relationship was observed between the maximum amounts of oxygen consumption and the activity of the quadriceps muscle group.