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Reliability and Discriminant Ability of an Instrumented Timed Up and Go Test in People With Postsurgical Orthopedic
Marica Giardini1, Ilaria Arcolin1, Valerio Antonio Arcobelli2
1Department of Physical Medicine and Rehabilitation, Institute of Veruno, Istituti Clinici Scientifici Maugeri IRCCS, Gattico-Veruno, Italy.
JMIR Rehabilitation and Assistive Technologies
|April 1, 2026
Summary
The smartphone-based instrumented Timed Up and Go (iTUG) test reliably measures functional mobility in orthopedic patients. Its sensor-derived metrics offer a multidimensional assessment, improving diagnostic accuracy beyond simple duration.
Area of Science:
- Biomedical Engineering
- Rehabilitation Medicine
- Digital Health
Background:
- The Timed Up and Go (TUG) test is a standard clinical tool for assessing mobility and fall risk.
- Instrumented TUG (iTUG) using inertial measurement units (IMUs) offers objective quantification but faces adoption barriers due to reliability and interpretability concerns.
- Smartphone integration of iTUG presents a feasible solution for wider clinical use.
Purpose of the Study:
- To evaluate the test-retest reliability of a single-sensor iTUG in orthopedic inpatients.
- To determine if reliable iTUG metrics can support multidimensional functional mobility assessment.
- To assess the ability of iTUG metrics to discriminate between common orthopedic conditions.
Main Methods:
- 104 orthopedic inpatients (post-THA, TKA, or femur fracture) performed a smartphone-based iTUG on two consecutive days.
- A single IMU was placed on the lower back.
- Variables with excellent test-retest reliability (ICC ≥0.75) were identified; factor analysis and discriminant analysis were employed.
Main Results:
- 36 out of 100 iTUG variables showed excellent reliability; 25 were used in multivariate analysis.
- Five mobility factors (walking ability, pace, sit-to-walk smoothness, turning, stability) explained 80.8% of variance.
- These factors achieved 68% classification accuracy (AUC 0.86) for differentiating orthopedic conditions, outperforming total iTUG duration (AUC 0.62).
Conclusions:
- Single-sensor iTUG provides reliable, clinically informative metrics for multidimensional functional mobility assessment in orthopedic patients.
- The smartphone-based approach is feasible, interpretable, and supports personalized rehabilitation monitoring.
- iTUG metrics enhance diagnostic capabilities beyond traditional measures, paving the way for digital health integration.
