The present study examined whether a sit-to-stand score can be related to the force-generating capacity of knee extensor muscles. Fifty-seven subjects (28 men, 63.0 ± 7.8 yrs, and 29 women, 64.2 ± 7.5 yrs, means ± SDs) performed a 10- repeated sit-to-stand test as fast as possible, on a steel molded chair. The time taken (Tsit-stand) was measured with a manual stopwatch. The leg length (L), defined as the distance from the great trochanter of the femur to the malleolus lateralis, was measured using a tape. A power index of the test (Psit-stand) was calculated by using the following equation: Psit-stand=(L-0.4)×body mass×g×10/Tsit-stand. The cross-sectional area of the quadriceps femoris muscle (CSAKE) and the maximal voluntary isometric knee extension force (FKE) were measured using MRI and a static myometer, respectively. There was no significant correlation between Tsit-stand and each of CSAKE and FKE. On the other hand, the Psit-stand was highly correlated with CSAKE and FKE, even after the influence of body mass and L was statistically eliminated. These results indicate that Psit-stand, derived from three variables of body mass, leg length, and time taken for a sit-to-stand test, can be a useful index to assess the force-generating capacity of the knee extensor muscles of elderly individuals.
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