Correlation Between Instrumented Timed Up and Go Test Performance and Muscle Strength in Knee and Hip Osteoarthritis: An Exploratory, Cross-Sectional Study.

Muscle weakness is a key contributor to functional limitation in individuals with hip (HOA) or knee osteoarthritis (KOA). Identifying accessible and objective tools to estimate muscle strength could improve clinical assessment and rehabilitation monitoring. This exploratory cross-sectional study investigated the relationship between parameters derived from the instrumented Timed Up and Go test (iTUG), and isokinetic quadriceps and hamstring strength in individuals with KOA or HOA. Thirty-six participants with KOA and 21 with HOA were assessed. Quadriceps and hamstring peak torques were measured at 60°/s using an isokinetic dynamometer. The iTUG was performed with a sacrum-mounted inertial measurement unit. Correlations between iTUG parameters and lower-limb muscle strength were weak-to-moderate in KOA (r = -0.398 to -0.516, p < 0.05) and moderate-to-strong in HOA (r= -0.537 to -0.843, p < 0.05). Total iTUG duration strongly correlated with the traditional stopwatch TUG (r = 0.91, p < 0.01), suggesting that the classic stopwatch-based TUG may offer comparable clinical insights to certain iTUG-derived temporal metrics. The iTUG test reflects lower-limb muscle weakness, especially in HOA, with vertical push-off power and temporal metrics showing the strongest relationships. These results support the use of iTUG as an accessible tool for estimating muscle weakness when isokinetic testing is unavailable. However, these findings should be interpreted with caution given the small sample size.