The aim of this study was to assess associations between performance in the timed up-and-go (TUG) and six-minute walk distance (6MWD) with physiological characteristics in young and old healthy adults. Thereto, we determined TUG, 6MWD, normalised jump power, centre of pressure displacement during 1-leg standing, forced expiratory volume in 1 s, percentage of age-predicted maximal heart rate (HR%) and height in 419 healthy young (men: 23.5 ± 2.8 years, women: 23.2 ± 2.9 years) and old (men: 74.6 ± 3.2 years, women: 74.1 ± 3.2 years) adults. Normalised jump power explained 8% and 19% of TUG in young (p = 0.025) and older men (p < 0.001), respectively. When fat mass percentage and age were added to normalised jump power, 30% of TUG was explained in older men (R2adj = 0.30, p < 0.001 to 0.106). Appendicular lean muscle mass percentage (ALM%) and age were the best determinants of TUG for older women (R2adj = 0.16, p < 0.001 to 0.01). HR% explained 17-39% of 6MWD across all groups (R2adj = 0.17 to 39, p < 0.001). In conclusion, in men, jump power was a key determinant for TUG, while in old women only it was the ALM%. As HR% was the most important determinant of 6MWD, motivational bias needs to be considered in the interpretation of this test.
Keywords: ageing; muscle; physical functional performance; spirometry.