Validity and reliability of a novel portable tension-gauge dynamometer for isometric and isotonic seated knee extension strength measurement.

Background: Accessible measurements of multimodal strength are essential to clinical practice and outcome research. While isokinetic dynamometers are considered the gold standard for isometric and isokinetic strength measurement, their practical use is limited by the insufficiency to measure isotonic strength, high cost, and needs for extensive physical space. Establishing techniques to assess isotonic strength using a portable dynamometer may enhance performance evaluations. Our objective was to determine the validity and test-retest reliability of isometric and isotonic knee extension strength measurements using a novel portable tension-gauge dynamometer.

Methods: Twenty recreationally active college-aged individuals participated. We recorded knee extension maximal voluntary isometric contraction (MVIC) force using both a tension-gauge dynamometer and an isokinetic dynamometer for validity and reliability. Peak isotonic knee extension force was recorded against external loads equivalent to 25 % and 30 % MVIC using the tension-gauge dynamometer for test-retest reliability during two sessions 7 days apart.

Results: We observed a very high correlation in the MVICs obtained between devices (r = 0.98, p < 0.001, R² = 0.96).We observed good-to-excellent reliability for MVIC force (ICC_3,1 = 0.94 [0.86, 0.98], p = 0.01), good-to-excellent reliability for peak isotonic force against external load at 25 % MVIC (ICC_3,1 = 0.95 [0.87, 0.98], p < 0.001), and excellent reliability for peak isotonic force against external load at 30 % MVIC (ICC_3,1 = 0.97 [0.93, 0.99], p < 0.001).

Conclusions: Valid and reliable force-based outcomes can be measured using a novel, tension-gauge dynamometer, which may provide relevant characteristics of muscle function for clinical and research uses.