I’m an overweight 59 year old slow runner - 13 min/mile with a VO2 max of 38 …. but Garmin thinks my max heart rate is 203 (autodetect) which is ludicrous! Using the old formula I’d guess closer to 160 would be more realistic . It’s been like this for months. It means none of my efforts ever really get recognised as such. I wear my watch 24/7 so what am I doing that causes this ? My runs are mainly 30-60 minutes maybe a couple of short walk beaks and I do a lot of walk activities.