Comparing ankle proprioception and balance in young and older sedentary adults

Abstract

Background. Ankle proprioceptive afferents are known to be crucial for the control of balance during standing and locomotion. The lower limb proprioceptive function declines with age, leading to an increased risk of falls. However, the effect of reduced proprioceptive function on balance in sedentary older adults is not well-studied. To address this question, this study assessed ankle position sense acuity and its relationship to static and dynamic balance in sedentary adults.Method. A total of 30 sedentary adults (young = 15, age: 25.1 ± 2.3 years, old = 15, age: 65.9 ± 8.4 years) participated in this study. Proprioception was assessed under two conditions: 1) in a passive assessment, the ankle was rotated passively to two positions: 1) a reference position (15° plantarflexion) and a comparison position smaller than the reference. Subsequently, participants verbally indicated which of the two positions was more plantarflexed. 2) During active assessment, participants actively matched the previously experienced position. The outcome measures for passive testing were: 1) a Just-Noticeable-Difference (JND) threshold and 2) an Uncertainty Area (UA) computed from the psychometric response-stimulus size difference function. The outcome measure for the active assessment was an Absolute Matching Error (AME), representing the angular difference between the two positions. Static balance was tested on the ground, and dynamic balance was tested using a stable and rocking balance board in open and closed eyes conditions. The outcome measure was the sway area of the body’s center of pressure (COP). Results. First, the median JND threshold was significantly higher in older adults compared to young adults (p = 0.02) with a large effect size (d = 0.96). No significant group differences were found for UA and AME. Second, the COP sway area was significantly larger in older adults during the on-ground open-eyes task (p < 0.05), but no significant differences were observed in other tasks. Third, for young adults, the COP sway area was quadratically correlated to the JND threshold during the on-ground eyes-closed task (p < 0.05, R² = 0.76). No other significant correlations between proprioceptive and sway measures were found. For older adults, the COP sway area was quadratically correlated to the JND threshold for all the dynamic tasks (R²: 0.58-0.77; p < 0.001) for all tasks. Discussion. This thesis provides empirical evidence that ankle proprioception declines with aging in the sedentary adult population. In sedentary older adults, the COP sway area tended to decrease during dynamic balance conditions. That is, they applied a "freezing" degree-of-freedom strategy to control their postural sway. This is a known strategy to address the fear of falling. The study highlights the complex interactions between age, proprioception, and balance. Recent evidence showed that physically active older adults do not show declined proprioceptive function, emphasizing the protective role of physical activity against age-related declines in proprioceptive function. Future studies may investigate the effect of proprioception training on the dynamic balance of sedentary adults.