The measures are a comparison between tests, not a measure of difference between the time intervals."Wearing a heart rate monitor, lie down for 10 minutes. Check your heart rate and then stand up. At 15 seconds after standing, check your heart rate again. Look at your hear rate again at 2 minutes. The 15-second, peak heart rate is usually interpreted to reflect parasympathetic nervous activity and the 2-minute heart rate sympathetic activity. They both are good indicators of overtraining."