Observing deviations from the norm in heart rate variability, such as an inability to reach expected maximum heart rates, can be informative for athletes.

“this is what I've been historically used for hair heart rate variability which tells me a lot more information this is what all the athletes also tell you like man my heart doesn't get up today you see on training pics you know you see when someone is fatigued they they do an interval and they know they always 100 80 185 let's say the lative threshold and today they cannot get up until more than 170 you see in the competition the first week of the two the France their maximum maximum heart rate let's say it's 195 last week the maximum heart rate is 170 right that's that's what I interpret by har variability”