目標：步行能力衰退是伴隨老化常見的現象。保持身體質量指數（Body Mass Index, BMI）適中和多運動皆有助於維持步行能力，但二者合併的效應則不清楚。本研究目的在探討BMI與運動對預防台灣中老年人步行能力衰退之組合效應。方法：本研究分析「中老年調查」2003及2007年的資料庫。排除非本人作答、嚴重心智功能缺損、中風及日常生活活動失能者，共有3,380位（加權後）50歲以上中老年人納入分析。依據受訪者二年度走完200-300公尺結果，評定其步行能力是否衰退。控制基本人口學、健康狀況及健康行為，以羅吉斯迴歸分析BMI與運動對步行能力衰退的個別和組合效應。結果：以個別變項分析中，肥胖（OR=1.75, p=0.001）及少運動（OR=1.37, p=0.036）與步行能力衰退有顯著關聯。在組合變項分析中，過輕且少運動者（OR=2.38, p=0.001）及肥胖且少運動者（OR=2.23, p=0.001）步行能力衰退的風險，皆明顯高於BMI適中且多運動者。結論：本研究之組合分析可彰顯同時保持BMI適中且多運動，對預防步行能力衰退的好處。研究結果讓民眾更容易及清楚地了解維持正常體重及日常運動對保有良好步行能力的重要，也可供健康促進政策之參考。

Objectives: A decline in walking ability is a well-known accompaniment of aging. Maintaining a healthy Body Mass Index (BMI) and a higher level of physical activity are helpful to prevent a decline in walking ability; however, the combined effect is not clear. The current study determined the combined effect of BMI and physical activity on the decline in walking ability amongst older Taiwanese. Methods: The 2003 and 2007 ＂Taiwan Longitudinal Study on Aging＂ datasets were analyzed. After exclusion of subjects not self-reported, with severe mental disorders, stroke, and disabilities in one or more activities of daily living, there were 3,380 subjects (weighted) ≥50 years of age included in the analysis. Study subjects were defined as having a decline if they exhibited negative changes in the ability to ＂walk 200-300 meters＂ between the two years. By controlling demographic, health status, and health behaviors, logistic regression was used to analyze the independent and combined effects of BMI and physical activity on the decline in walking ability. Results: When analyzed independently, obesity (OR = 1.75, p = 0.001) and less physical activity (OR = 1.37, p = 0.036) were associated with a decline in walking ability. Based on an analysis of the combination of BMI and physical activity, subjects who were underweight and engaged in less physical activity (OR = 2.38, p = 0.001) and subjects who were obese and engaged in less physical activity (OR = 2.23, p = 0.001) were more likely to have a decline in walking ability than subjects who had a BMI in the healthy range and engaged in more physical activity. Conclusions: The combined analysis method demonstrated the advantage of maintaining a healthy BMI and a higher level of physical activity simultaneously to prevent a decline in walking ability. The results of the current study should help people more easily and clearly understand the importance of a healthy BMI and physical activity to maintain good walking ability, and provide the basis for a national policy regarding health promotion.