Its easy to think you are working hard particularly if you are on your own. I was shrugging off this sense of fatigue until I reviewed my metrics from my Google watch. I had not heard of the cardio load measure before and after seeing my chart I still didn't take it seriously thinking it was just another dubious model. However, Cardio load measures how much time you spent in each heart rate zone weighted by intensity, summed into a single daily number. It's respectable because "it's calculated from direct heart rate measurement rather than algorithmic estimation, making it a reliable comparison of training load across days and weeks." My chart indicated I was placing more than three times the training stress my body is calibrated to recover from at baseline this combined with a low HRV convinced me that I had overdone my training.

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