Complete any 10 unique workouts (there are some as short as 2 minutes, but most are at least 5 minutes) and this will unlock.
There are only 9 types that come with the game. There are others you can pay for. So you'll need to do at least 2 workouts of the same type. I had 2 abs and 1 in the rest when this popped. I achieved the achievement The Whole Package at the same time since my 10th workout was also the last type I needed.
Keep doing more workouts to unlock the following achievements.