Development of the lateral equilibrium reaction in stance

The lateral equilibrium reaction in stance was assessed in 80 normally developing children aged from nine months to five years. A scoring system and checklist were devised to describe the character and presence of the reaction. The earliest non-functional response was seen at nine months of age, and no functional response was observed to both sides until after two years of age. A progressive increase in functional response to both directions of tilt occurred between 12 and 18 months, with an unexpected drop at 21 and 24 months. All three-year-old and five-year-old children demonstrated a functional response to both sides. The lower extremity pattern was the most consistent component observed in those with a functional response. Individual variations in movements of the trunk, upper extremities and head excluded any indication of developmental patterns for these body segments. The clinical implications of these results are discussed.