Like any athlete in a race, the quick exertion of a run requires more oxygen then the body can adequately deliver so the muscles generate a substance called lactate. Any excess lactate produced turns to lactic acid when the race is over. By walking your horse, you eliminate the excess lactic acid that could cause sore muscles.
Once the body slows down, oxygen becomes available allowing continued aerobic metabolism and energy for the body's recovery from the strenuous event. Walking removes any excess lactic acid that might have accumulated.
This is a very simple explanation of a very complex issue. Exercise physiologists are actively researching delayed-onset muscle soreness in response to extreme exercise. On-going discussions actively strive for potential prevention and treatment of muscle soreness.
Comments will be approved before showing up.