My thesis investigates the fatigue levels in firefighters and athletes using the Rusko Test and RUST ECG Test, measured through a Polar Variety Sensor heart rate monitor. The study aims to understand the physiological responses to stress and recovery patterns in these high-intensity professions by analyzing heart rate variability and other cardiovascular metrics. The findings will contribute to developing tailored recovery protocols and enhancing performance while minimizing the risk of overtraining and injuries in both firefighters and athletes.