Although the total "Timed-Up-and Go" test (TUG) performance time can characterize an age-related decline of general mobility, this result alone doesn't give any detailed information about the test subtasks. The primary objective of the study was to identify in nursing home women a variable extracted from instrumented TUG (iTUG) that is the best predictor of age. The secondary objective was to assess whether this variable is associated with the results of the isometric knee extension peak torque (IKEPT); lower limb strength measured by the 30-s chair stand test (30sCST), and walking capacity measured by the 6-min walk test (6MWT). Twenty-six women (mean ± SD: age-85.8 ± 3.6 years; body weight-59.4 ± 12.3 kg; body height-151.0 ± 7.3 cm; BMI-26.0 ± 4.9 kg/m2) performed iTUG (while wearing a body-fixed inertial sensor) and functional tests. Total iTUG performance time significantly correlated with age (r = 0.484; p < 0.05), 30sCST (r = -0.593; p < 0.01), and 6MWT (r = -0.747; p < 0.001) but not with absolute nor relative IKEPT (p > 0.05). Additionally, the subjects' age correlated with 30sCST (r = -0.422; p < 0.05), 6MWT (r = -0.482; p < 0.05), IKEPT (r = -0.392; p < 0.05) and IKEPT/FFM (r = -0.407; p < 0.05). Five out of 16 analyzed iTUG variables were significantly related to age, and multiple regression analysis showed the best correlation with the sit-to-stand vertical acceleration range (STSVAR) (r2 = 0.430; SEE = 3.041; β = -0.544 ± 0.245; B = -1.204 ± 0.543; p < 0.05). Moreover, STSVAR was significantly associated with %Fat (r = 0.415; p < 0.05), 30sCST (r = 0.519; p < 0.01), 6MWT (r = 0.585; p < 0.01) but not with absolute nor relative IKEPT (p > 0.05). The obtained results suggest that in the oldest old group of nursing home women an age-related decline in TUG performance is mainly associated with a reduction of "explosive" strength of lower limb muscles.
Keywords: Acceleration; Aged; Functional capacity; Inertial unit; Knee extension; Muscle strength.