Triathletes religiously track Heart Rate (HR). As they should. It’s a great stress metric. It monitors the stress load a body is used to handling as well as what load it can take during strenuous training. Unfortunately, relying on your resting heart rate isn’t the most accurate way to know if you’ve recovered from your previous workout. But take heart (literally) because there’s a relatively new heart-related metric in endurance training. It’s Heart Rate Variability (HRV). And, simply stated, if you're not using it yet, you will be. The Importance of Heart Rate Variability HRV offers a window into the “flexibility of our nervous system” which can be used to guide an optimal triathlon training program. As triathletes well know,…