From Chair to Force: Sit‐to‐Stand–Derived Power for Estimating Lower‐Limb Muscle Strength
Hilal Denizoglu Kulli, Hamide Turan, Onur TuranRationale
Sit‐to‐stand (STS) tests are practical tools used in routine clinical assessment of lower‐limb function. However, whether STS‐derived power can serve as a surrogate for directly measured muscle strength remains uncertain, particularly across different test durations.
Aims and Objective
To examine associations between STS‐derived power from 10‐, 30‐, and 60‐s protocols and HHD‐measured lower‐limb strength, and to evaluate whether sex‐adjusted STS‐based estimates provide sufficient agreement with directly measured strength to inform their potential clinical use.
Methods
In this cross‐sectional study, 66 adults aged 18–25 years (33 women, 33 men) completed the three STS protocols in randomized order. Bilateral isometric strength of the knee extensors and flexors and hip flexors, extensors, and abductors were assessed using a manually stabilized HHD make‐test. STS power was calculated using a biomechanically based equation. Associations were examined using Spearman’s correlations. Sex‐adjusted regression models for knee flexor, hip abductor, and lower‐limb composite score were internally validated using repeated 10‐fold cross‐validation. Differences between measured and cross‐validated predicted strength values were examined using Bland–Altman analysis.
Results
STS‐derived power correlated positively with all strength outcomes ( ρ = 0.496–0.777; all p < 0.001). In sex‐adjusted models, STS power was associated with knee flexor and hip abductor strength across all protocols and with composite strength for the 10‐ and 60‐s protocols. Cross‐validated R 2 ranged from 0.650 to 0.665, 0.531 to 0.557, and 0.652 to 0.662 for knee flexor, hip abductor, and composite strength, respectively. Mean measured‐minus‐predicted differences were near zero; however, limits of agreement were wide and proportional bias was present.
Conclusion
Although STS‐derived power is associated with lower‐limb isometric strength, its limited individual‐level predictive precision does not support its use as a substitute for HHD assessment. In routine clinical practice, STS testing should be interpreted as a multidimensional measure of functional performance that provides complementary rather than interchangeable information about lower‐limb muscle strength.