I think you've got the lactate shuttle a little wrong mate, the way I understood it worked was...

  1. Pyruvate (pyruvic acid) is formed when glycogen and glucose are being broken down at high rates in your muscles (called glycolysis which is the conversion of these into pyruvate). Pyruvate is then converted to Lactate (lactic acid) as it increases in the muscles.
  2. Lactate is now formed and transported away from the muscle cells into surrounding tissue and blood. This allows glycolysis to persist and thus continuing the supply of energy to our muscles.
  3. The muscle cells which the lactate is transported to can cause the lactate to be broken down to fuel (mainly ATP) or can be used to build glycogen.