Body and Brain Connection

The major pain about getting this achievement is finding people to play the game with locally. What makes that "problem" easier, is that the only time that other people need to be scanned with you (i.e., so that the game knows there is more than 1 person playing the group exercise) is right before the first group exercise begins. After each group exercise is finished, you can select "try again" and you'll be able to play another exercise without the game having to verify that there is someone playing the game with you. The other person/people can leave without having to play it with you if they don't want to.

Note that this can still take a decent chunk of time as even a 2-player group exercise takes the better part of 10 minutes.