Decreased Muscle Strength in Older Adults With Type 2 Diabetes
Adequate skeletal muscle strength is essential for physical functioning and low muscle strength is a predictor of physical limitations. Older adults with diabetes have a two- to threefold increased risk of physical disability. However, muscle strength has never been investigated with regard to diabetes in a population-based study. We evaluated grip and knee extensor strength and muscle mass in 485 older adults with diabetes and 2,133 without diabetes in the Health, Aging, and Body Composition study. Older adults with diabetes had greater arm and leg muscle mass than those without diabetes because they were bigger in body size. Despite this, muscle strength was lower in men with diabetes and not higher in women with diabetes than corresponding counterparts. Muscle quality, defined as muscle strength per unit regional muscle mass, was significantly lower in men and women with diabetes than those without diabetes in both upper and lower extremities. Furthermore, longer duration of diabetes (≥6 years) and poor glycemic control (HbA_1c >8.0%) were associated with even poorer muscle quality. In conclusion, diabetes is associated with lower skeletal muscle strength and quality. These characteristics may contribute to the development of physical disability in older adults with diabetes.

In the U.S., people aged 65 years and older will make up most of the diabetic population in the next 25 years. Furthermore, the proportion of the diabetic population aged 75 years and older is projected to exceed 30% by 2050. In older adults, diabetes has been associated with a two- to threefold increased risk of developing physical disability. Moreover, we have reported the association of diabetes with subclinical functional limitation in the Health, Aging, and Body Composition (Health ABC) study. However, the mechanism for impaired physical function in diabetes has been poorly understood. Chronic conditions frequently combined with diabetes, such as coronary heart disease, peripheral artery disease, visual impairment, and depression, partially explained the association, but still 40% of excess risk for physical disability remained unexplained.

Low muscle strength, but not muscle mass, is associated with poor physical function in older men and women. Muscle strength measured in midlife or old age is highly predictive of functional limitations and disability up to 25 years later. However, the effects of diabetes on muscle strength and quality have never been investigated in a population-based study. Because most individuals with diabetes are obese and have bigger muscle mass and increased total body fat mass, direct comparison of their muscle strength with those without diabetes may be misleading. With the advent of body composition analysis, we are now able to precisely measure regional muscle mass and quantitatively assess in vivo skeletal muscle quality defined as maximal voluntary contractile force or torque per unit regional muscle mass of the specific body compartment.

In the present study, we evaluated hand grip and knee extensor strength and muscle quality in community-dwelling older adults with and without diabetes in the Health, Aging, and Body Composition Study. To evaluate the cumulative effects of metabolic derangements of diabetes on skeletal muscle function, subjects with diabetes were further categorized by the duration of diabetes and the level of glycemic control.