Monitoring training load is essential for understanding athlete fatigue and optimizing performance. This review discusses various methods for monitoring external and internal loads, including power output, time-motion analysis, neuromuscular function, heart rate, RPE, lactate, and HR recovery. These measures help determine an athlete's adaptation to training and minimize the risk of overreaching, injury, and illness. While no single marker is definitive, combining multiple measures provides a more accurate picture of fatigue. Individualized monitoring is crucial, as athletes may respond differently to training stimuli. Effective monitoring systems should be intuitive, provide efficient data analysis, and enable clear feedback. Current practices include using self-report questionnaires, performance tests, and GPS tracking. Team and individual sports require different approaches, with team sports often involving more complex assessments. A systems-based approach integrating data from various sources is recommended for effective fatigue management. The review highlights the importance of individualized monitoring and the need for accurate, interpretable feedback to enhance training outcomes and athlete well-being.Monitoring training load is essential for understanding athlete fatigue and optimizing performance. This review discusses various methods for monitoring external and internal loads, including power output, time-motion analysis, neuromuscular function, heart rate, RPE, lactate, and HR recovery. These measures help determine an athlete's adaptation to training and minimize the risk of overreaching, injury, and illness. While no single marker is definitive, combining multiple measures provides a more accurate picture of fatigue. Individualized monitoring is crucial, as athletes may respond differently to training stimuli. Effective monitoring systems should be intuitive, provide efficient data analysis, and enable clear feedback. Current practices include using self-report questionnaires, performance tests, and GPS tracking. Team and individual sports require different approaches, with team sports often involving more complex assessments. A systems-based approach integrating data from various sources is recommended for effective fatigue management. The review highlights the importance of individualized monitoring and the need for accurate, interpretable feedback to enhance training outcomes and athlete well-being.