var findBy = {
    _id : bWYqm6-Oo,
    exercises : [
      {
        date: {
          $gte: 2019-09-22,
          $lt: 2019-09-22
        }
      }
    ]
  }
  UserModel.find(findBy).limit(5).exec((err, data) => {
      (err) ? res.json({"error" : "problem searching for exercises: " + err}) :  res.json(data);
  });

{
    _id: "bWYqm6-Oo",
    user: "rommy",
    exersises: [
        {
        user_id: "bWYqm6-Oo",
        date: "2019-09-20T00:00:00.000Z",
        description: "stiup",
        duration: "22",
        _id: "pu90D-dHx"
        },
        {
        user_id: "bWYqm6-Oo",
        date: "2019-09-21T00:00:00.000Z",
        description: "pushup",
        duration: "22",
        _id: "YtfsJLOXb"
        },
        {
        user_id: "bWYqm6-Oo",
        date: "2019-09-20T00:00:00.000Z",
        description: "stiup",
        duration: "22",
        _id: "pu90D-dHx"
        },
        {
        user_id: "bWYqm6-Oo",
        date: "2019-09-24T00:00:00.000Z",
        description: "stiup",
        duration: "22",
        _id: "pu90D-dHx"
        }
    ],
    __v: 9
}