The Yo-Yo Intermittent Recovery (IR) tests, specifically Level 1 (Yo-Yo IR1) and Level 2 (Yo-Yo IR2), are valuable tools for evaluating an individual's ability to perform repeated intense exercise, particularly in sports with high intermittent demands such as basketball and soccer. The Yo-Yo IR1 test focuses on aerobic capacity, while the Yo-Yo IR2 test assesses anaerobic recovery. Elite athletes in various sports show better performance in these tests, and young athletes' performance improves with age. The Yo-Yo IR tests are more sensitive than maximum oxygen uptake (VO2max) tests for detecting performance changes. These tests have been widely adopted in sports science and team sports to evaluate players' abilities to perform high-intensity exercise repeatedly. The tests consist of 2 × 20m shuttle runs at increasing speeds, interspersed with 10-second active recovery periods. The physiological response to these tests includes progressive increases in heart rate and oxygen uptake, with faster increases in the IR2 test. The article discusses the physiological response, use in sports analysis, age-related performance, seasonal variations, and the application of reduced versions of the tests.The Yo-Yo Intermittent Recovery (IR) tests, specifically Level 1 (Yo-Yo IR1) and Level 2 (Yo-Yo IR2), are valuable tools for evaluating an individual's ability to perform repeated intense exercise, particularly in sports with high intermittent demands such as basketball and soccer. The Yo-Yo IR1 test focuses on aerobic capacity, while the Yo-Yo IR2 test assesses anaerobic recovery. Elite athletes in various sports show better performance in these tests, and young athletes' performance improves with age. The Yo-Yo IR tests are more sensitive than maximum oxygen uptake (VO2max) tests for detecting performance changes. These tests have been widely adopted in sports science and team sports to evaluate players' abilities to perform high-intensity exercise repeatedly. The tests consist of 2 × 20m shuttle runs at increasing speeds, interspersed with 10-second active recovery periods. The physiological response to these tests includes progressive increases in heart rate and oxygen uptake, with faster increases in the IR2 test. The article discusses the physiological response, use in sports analysis, age-related performance, seasonal variations, and the application of reduced versions of the tests.