Genetic effects in common on maximal walking speed and muscle performance in older women.

The purpose was to examine whether maximal walking speed, maximal isometric knee extensor strength, and leg extensor power share genetic or environmental effects in common. The data was collected from 103 monozygotic and 114 dizygotic female twin pairs aged 63-76 years. Maximal walking speed over 10 m was measured in the laboratory corridor using photocells for timing. Isometric knee extensor strength and leg extensor power were measured using an adjustable dynamometer. The genetic models showed that strength, power, and walking speed had a genetic effect in common which accounted for 52% of the variance in strength, 36% in power, and 34% in walking speed. Strength and power had a non-shared environmental effect in common explaining 13% of variation in strength and 14% in power. The remaining variance was accounted for by trait-specific effects. Some people may be more prone to functional limitation in old age due to their genetic disposition, but this does not rule out that changes in the lifestyle of predisposed subjects may also have a major effect. Approximately half of the variation in each trait was explained by environmental effects, which suggests the importance of the physical activity to improve performance and prevent functional limitation.