gistfile1.json

//definitions
{version:1,
 id: <objId>
 key-that-means-workout: {
   //however you represet the whole nested tree
   exercise: 12329-218231-12321-128184923,
   expected: 12
 }
}

// after update
{version:2,
 id: <same ojbId>,
 key-that-means-workout: {
   //however you represet the whole nested tree
   exercise: 12329-218231-12321-128184923,
   expected: 12,
   exercise: 9784987-23423-324-2342342,
   expected: 10
 }
}

gistfile2.json

//workout records
{version: 1,
 implemented: <parent objId>,
 complete-date: 2014-05-01,
  results: {
    exercise:12329-218231-12321-128184923,
    expected: 12,
    actual: 11
  }
}

//someone else, started doing this later
{version:2,
 implemented: <parent objId>,
 complete-date: 2014-05-07,
 results: {
   //however you represet the whole nested tree
   exercise: 12329-218231-12321-128184923,
   expected: 12,
   actual: 10,
   exercise: 9784987-23423-324-2342342,
   expected: 10,
   actual: 11
 }
}