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Differences in Ground Reaction Force During Foot Strength Testing in Sitting and Standing Positions
Karen M Stevens1, Maxine L Olson1, Frank E DiLiberto1
1Department of Physical Therapy, Rosalind Franklin University of Medicine and Science, North Chicago, IL, USA.
Journal of Applied Biomechanics
|December 6, 2025
Summary
Standing foot strength testing yields greater force output than sitting. Changes in ground reaction force (GRF) correlate with strength, suggesting standing enhances rearfoot stability for improved clinical assessment.
Area of Science:
- Biomechanics
- Human Movement Science
- Clinical Assessment
Background:
- Foot strength is crucial for mobility, balance, and overall function, yet its accurate measurement remains challenging.
- Understanding the biomechanical differences between sitting and standing positions during foot strength testing is essential for enhancing clinical utility.
- Changes in ground reaction force (GRF) may offer insights into observed strength variations between different test postures.
Purpose of the Study:
- To investigate whether changes in ground reaction force (Δ GRF) differ between sitting and standing foot strength tests.
- To determine the association between Δ GRF and measured foot strength in both test positions.
- To provide evidence-based recommendations for optimizing clinical foot strength assessments.
Main Methods:
- Twenty healthy adults (mean age 24.7 years) participated in the study.
- Participants were randomly assigned to either a sitting or standing initial test position.
- Foot strength and 3D Δ GRF were measured using a force plate and a scale while subjects performed a towel curl task with their toes.
Main Results:
- Mean peak foot strength and anterior-posterior GRF (Δ GRFx) were significantly greater in the standing position (P < .001).
- Strong correlations were observed between sitting and standing peak strength (r = .703).
- Peak strength showed strong correlations with Δ GRFx (r = .738) and superior-inferior GRF (Δ GRFz = .595) in the standing position.
Conclusions:
- Higher strength production in standing, correlated with Δ GRF, aligns with task demands and highlights the role of rearfoot stability.
- The standing position appears more effective for assessing maximal foot strength due to greater force production and GRF engagement.
- Clinical assessment of foot strength is recommended in the standing position over the sitting position for improved validity and reliability.
