Here is the full list of all 23 Sexy Fitness Girl achievements.
Level 4 fully unlocked
Eliminate 500 times
Complete level 2
Complete level 3
Maid 100% intimacy
Level 3 fully unlocked
Complete level 1
Nurse 100% intimacy
Level 2 fully unlocked
OL 100% intimacy
Level 1 fully unlocked
Eliminate 100 times
Eliminate 50 times
Eliminate 10 times
Complete level 4
Complete level 5
Sister 100% intimacy
Flight attendant 100% intimacy
Level 5 fully unlocked
Eliminate 1000 times
Eliminate 2000 times
Eliminate 5000 times
Eliminate 10000 times