The article tells me more about the dangers of overtraining at an advanced age than the usefulness of wearables. The wearable was useful for the researchers after the person had already passed away.

Also, considering the number of such workouts he completed and the fact that it seems he was aware of his deteriorating heart, he carried on? Even despite reported fatigue? Mad respect for his determination.

76 (already a good age) with an existing heart condition and increases HIIT exercise frequency by 25%.

I wonder if they consulted their physician before doing that, and what they recommended?