筋力と筋力低下が高齢者の移動能力低下の予測因子

筋力と筋力低下が高齢者の移動能力低下の予測因子という論文を紹介します。

Gregory E. Hicks, et al: Absolute Strength and Loss of Strength as Predictors of Mobility Decline in Older Adults: The InCHIANTI Study. J Gerontol A Biol Sci Med Sci (2011) doi: 10.1093/gerona/glr055

この研究では前向きコホートで、一時点の筋力だけでなく3年間の筋力変化が、高齢者の移動能力低下の予測因子となるかどうかを調査しているのが特徴です。

結果として一時点の筋力の場合、男性では膝伸展筋力19.2kg未満と握力39kg未満の場合に、歩行速度が0.24m/s低下します。これは臨床的にも有意です。女性では歩行速度が0.06m/s低下しますが、これは臨床的な有意差ではありませんでした。

一方、3年間の筋力変化で見た場合、男性、女性とも移動能力の低下を予測できませんでした。これより3年間の筋力変化よりも、一時点の筋力のほうが特に男性の場合に3年後の移動能力低下を予測できるという結論です。

3年間の筋力変化で、その後の3年間の筋力変化を予測できないというのは興味深いです。直線上に加齢による筋力低下が進行していくわけではないのかもしれません。

Abstract
Background.Theoretical definitions of sarcopenia traditionally emphasize age-related loss of muscle strength; however, most analyses of the association between strength and mobility examine strength at a single time point. This study sought to identify sex-specific cutpoints for muscle strength and power (at one time point) and 3-year changes in strength and power that would maximize prediction of 3-year mobility decline.

Methods.Longitudinal analysis of 934 adults aged ≥65 years enrolled in the Invecchiare in Chianti study was conducted. Grip strength, knee extension strength, and lower extremity power were measured at baseline and 3 years postenrollment. Mobility function (gait speed and self-reported mobility disability) was measured at 3 and 6 years postenrollment. Classification and regression tree analysis was used to predict mobility decline from Years 3 to 6.

Results.Men with knee extension strength <19.2 kg and grip strength <39.0 kg had clinically meaningful declines in gait speed of .24 m/s. Furthermore, men with power <105 W were nearly nine times more likely to develop incident mobility disability (likelihood ratio = 8.68; 95% confidence interval = 3.91, 19.44). Among women, knee extension strength <18.0 kg was associated with a minimal gait speed decline of 0.06 m/s, and women with leg power <64 W were three times more likely to develop incident mobility disability (likelihood ratio = 3.01; 95% confidence interval = 1.79, 5.08). Three-year changes in strength and power did not predict mobility decline in either sex.

Conclusions.Findings suggest that strength and power measured at one time point are more predictive of mobility decline than 3-year changes and that low strength and power are particularly powerful risk factors in men.