The significance of heart rate variability (HRV) in fitness lies in its ability to reflect the body’s autonomic nervous system function and overall health. A higher HRV indicates better cardiovascular fitness, resilience to stress, and an ability to recover from exertion. Conversely, low HRV can be a marker of stress, fatigue, or impending illness. Monitoring HRV can provide valuable insights for athletes to optimize training regimens and ensure adequate recovery. By respecting the body's signals, individuals can enhance performance while minimizing the risk of injury and overtraining.