Validity and Test-Retest Reliability of a Novel Push Low-Cost Hand-Held Dynamometer for Knee Strength Assessment during Different Force Ranges

Abstract

The objective was to assess the instrumental validity and the test-retest reliability of a low-cost hand-held push dynamometer adapted from a load-cell based hanging scale (tHHD) to collect compressive forces in different ranges of compressive forces. Three independent raters applied 50 pre-established compressions each on the tHHD centered on a force platform in three distinct ranges: ~70 N, ~160 N, ~250 N. Knee isometric strength was also assessed on 19 subjects in two sessions (48 h apart) using the tHHD anchored by an inelastic adjustable strap. Knee extension and flexion were assessed with the participant seated on a chair with the feet resting on the floor, knees, and hips flexed at 90°. The isometric force peaks were recorded and compared. The ICC and the Cronbach's α showed excellent consistency and agreement for both instrumental validity and test-retest reliability (range: 0.89-0.99), as the correlation and determination coefficients (range: 0.80-0.99). The SEM and the MDC analysis returned adequate low values with a coefficient of variation less than 5%. The Bland-Altman results showed consistency and high levels of agreement. The tHHD is a valid method to assess the knee isometric strength, showing portability, cost-effectiveness, and user-friendly interface to provide an effective form to assess the knee isometric strength.

Keywords: isometric contraction; knee assessment; muscle strength.

Conflict of interest statement

M.A.B. is the commercial director of MED.DOR Ltd. The other authors declare no conflict of interest.

Figures

Figure 1

The push low-cost hand-held dynamometer.

Figure 2

Experimental set-up. tHHD = tested dynamometer; FP = force platform; sCAM = synchronized camera.

Figure 3

Validity analysis—Bland–Altman Plots. (a) ~70 N: bias = 4.81 (95% confidence interval [CI] = 4.41 to 5.21); lower limit of agreement (LLA) = 2.06 (95% CI = 1.37 to 2.74); upper limit of agreement (ULA) = 7.56 (95% CI = 6.88 to 8.25). (b) ~160 N: Bias = 5.70 (95% CI = 5.03 to 6.38); LLA = 1.07 (95% CI = −0.08 to 2.22); ULA = 10.34 (95% CI = 9.18 to 11.50). (c) ~250 N: bias = 7.99 (95% CI: 6.38 to 9.58); LLA = −3.06 (95% CI: −5.81 to −0.30); ULA = 19.03 (95% CI: 16.27 to 21.78).

Figure 4

Test–retest reliability analysis—Bland–Altman Plots. (a) Flexion: bias = −2.21 (95% confidence interval [CI] = −3.87 to −0.55); lower limit of agreement (LLA) = −10.08 (95% CI = −12.95 to −7.21); upper limit of agreement (ULA) = 5.65 (95% CI = 2.78 to 8.52). (b) Extension: bias = −0.60 (95% CI = −2.56 to 1.36); LLA = −9.91 (95% CI = −13.31 to −6.52); ULA = 8.70 (95% CI = 5.31 to 12.10).