Heart rate reserve (HRR) influences training intensity by determining the target heart rate zone for workouts. HRR is calculated by subtracting resting heart rate from maximum heart rate. This allows individuals to assess their fitness level and adjust exercise intensity accordingly. Higher HRR indicates better cardiovascular fitness, enabling athletes to train at higher intensities. Utilizing HRR helps to optimize cardiovascular training, ensuring that workouts are effective and aligned with fitness goals, whether for endurance or fat loss.