Unlock Ultimate Balance Test/Scale Challenge
At the statistics screen (The screen after you choose your mii), there is the balance board character running on a treadmill in the background. Click him with your pointer and you will be asked if you would like to participate in the ultimate balance test or scale challenge.
Unlock challenges
Parrallel stretch challenge - Get 4 stars in both the 30 sec and 60 sec workout.
Jackknife challenge - Get 4 stars in both the 10 sec workout and the 20 sec workout.
Pressup challenge - Get 4 stars on both the 6 reps and 10 reps mode.