The Yo-Yo Intermittent Recovery (IR) tests are useful tools for evaluating physical performance in intermittent sports. These tests assess an individual's ability to perform repeated intense exercise. The Yo-Yo IR1 test focuses on aerobic capacity, while the Yo-Yo IR2 test evaluates anaerobic capacity. Elite athletes perform better in these tests as competition level increases. Performance in these tests improves with age in young athletes. The Yo-Yo IR tests are more sensitive than maximal oxygen uptake (VO2max) in detecting performance changes. They provide a simple and valid way to assess an individual's capacity for repeated intense exercise. Many sports with intermittent exercise, such as basketball and soccer, have high physical demands due to brief, intense activities. Physiological responses, such as heart rate and metabolic measurements, show that aerobic and anaerobic energy systems are heavily used during competition. Traditional tests like the Legér shuttle-run test and VO2max have been questioned for their relevance to intermittent sports, leading to the development of the Yo-Yo IR tests. These tests are now widely used in sports science due to their specificity and practicality. The Yo-Yo IR tests were inspired by the Legér test, involving 20m shuttles with recovery periods. The tests consist of 2x20m shuttle runs at increasing speeds, with active recovery periods. The Yo-Yo IR1 test focuses on endurance, while the Yo-Yo IR2 test evaluates anaerobic capacity. These tests have been used in various sports, including basketball, soccer, rugby, and Australian football. After over 15 years of application, the potential and use of these tests are now being evaluated. The article presents data on physiological responses, test use in sports analysis, age effects, seasonal variations, and reduced test versions. The tests are effective in assessing performance in intermittent sports.The Yo-Yo Intermittent Recovery (IR) tests are useful tools for evaluating physical performance in intermittent sports. These tests assess an individual's ability to perform repeated intense exercise. The Yo-Yo IR1 test focuses on aerobic capacity, while the Yo-Yo IR2 test evaluates anaerobic capacity. Elite athletes perform better in these tests as competition level increases. Performance in these tests improves with age in young athletes. The Yo-Yo IR tests are more sensitive than maximal oxygen uptake (VO2max) in detecting performance changes. They provide a simple and valid way to assess an individual's capacity for repeated intense exercise. Many sports with intermittent exercise, such as basketball and soccer, have high physical demands due to brief, intense activities. Physiological responses, such as heart rate and metabolic measurements, show that aerobic and anaerobic energy systems are heavily used during competition. Traditional tests like the Legér shuttle-run test and VO2max have been questioned for their relevance to intermittent sports, leading to the development of the Yo-Yo IR tests. These tests are now widely used in sports science due to their specificity and practicality. The Yo-Yo IR tests were inspired by the Legér test, involving 20m shuttles with recovery periods. The tests consist of 2x20m shuttle runs at increasing speeds, with active recovery periods. The Yo-Yo IR1 test focuses on endurance, while the Yo-Yo IR2 test evaluates anaerobic capacity. These tests have been used in various sports, including basketball, soccer, rugby, and Australian football. After over 15 years of application, the potential and use of these tests are now being evaluated. The article presents data on physiological responses, test use in sports analysis, age effects, seasonal variations, and reduced test versions. The tests are effective in assessing performance in intermittent sports.