Do you check your heart rate often on the 100s on 1:20?
I am 52 male, swimming again for about a year to build up base. last swam serious age 22 (4:59 500, :49 100) Now I swim 5-6 times a week, 4000 yds. Goal is to break 6mins. in the 500. Swam first masters meet last weekend. Wanted to go 6:30 (15,20,20,20,15) but went 6:52 (13,26,26,27,20). Almost the same splits as the 1650 I swam. (24:14)
When I shorten up the 100s interval (I usually go 2:00 or 1:45), my heart rate goes up to 180. I thought max should be 220-age, so about 168.