Investigation of a Low-cost Portable Inline Dynamometer for Measuring Isometric Knee Extensor Strength

Area of Science:

• Biomechanics and Kinesiology
• Rehabilitation Engineering
• Sports Science

Background:

• Isometric strength testing is crucial for assessing deficits and monitoring progress in rehabilitation and training.
• The accuracy of low-cost inline force sensors compared to expensive lab-based dynamometers remains unclear.

Purpose of the Study:

• To evaluate the agreement between a lab-based dynamometer and low-cost inline force sensors (wireless and wired) for measuring isometric knee extension torque.

Main Methods:

• Prospective cross-sectional study involving 14 healthy adults.
• Measurements of peak isometric knee extension torque at 90°, 45°, and 15° using a Humac dynamometer, a wireless Tindeq sensor, and a wired MLP sensor.
• Agreement assessed via Pearson's Correlation, ICC, MDC, and Bland-Altman LOA; voluntary activation (VA) quantified using electrical stimulation.

Main Results:

• The Tindeq wireless sensor demonstrated minimal bias compared to the Humac dynamometer across knee angles.
• Bland-Altman Limits of Agreement (LOA) were relatively large, indicating potential for significant individual measurement errors.
• Inline sensors (Tindeq and MLP) showed high agreement with each other (ICC > 0.94) but lower agreement with the lab-based dynamometer (ICC < 0.80).

Conclusions:

• Low-cost wireless force sensors like Tindeq show potential for clinical applications in strength assessment.
• Despite small bias, large LOA necessitate cautious interpretation of individual measurements from these devices.
• Further validation with larger sample sizes and repeated testing sessions is recommended.