Reliability and validity of knee extensor strength measurements using a portable dynamometer anchoring system in a supine position

Abstract

Background Muscle strength measurements using hand-held dynamometry (HHD) can be affected by the inadequate strength of the tester and lack of stabilization of the participants and the device. A portable HHD anchoring system was designed that enabled the measurement of isometric knee extensor muscle strength in a supine position. This can be used with individuals who are unable to assume the sitting position required for the measurement of knee extensor strength in conventional isokinetic dynamometry (IKD). The aim of this study was to evaluate the reliability and validity of knee extensor strength measurements using this device. Methods The maximal knee extensor isometric strength of the dominant leg in healthy adults aged 20 to 40 years was tested. Three trials of three contractions were assessed by two raters using the portable dynamometer anchoring system whilst the participant was in the supine position. After the three measurement trials, peak knee extensor torque was evaluated using IKD. The intraclass correlation coefficient (ICC) and 95% limits of agreement (LOA) for intra- and inter-rater reliability were obtained. Results Thirty-nine participants (19 male and 20 female, aged 30.08 ± 4.16 y), completed the three measurement trials. The ICC for intra-rater reliability was 0.98 for the maximum measurements of knee extensor strength (95% confidence interval [CI]: 0.96–0.98) and 0.98 (95% CI: 0.96–0.99) for inter-rater reliability. The mean difference (%) between the maximum knee extensor strength measurements of each trial was 1.02% (LOA range: − 11.13 to 13.16%) for intra-rater and − 1.44% (LOA range: − 13.98 to 11.08%) for inter-rater measurements. The Pearson correlation coefficient of the maximum voluntary peak torque measurements with the portable dynamometer anchoring system and IKD was 0.927. Conclusions The portable dynamometer anchoring system is a reliable and valid tool for measuring isometric knee extensor strength in a supine position. Future clinical feasibility studies are needed to determine if this equipment can be applied to people with severe illness or disabilities. Trial registration KCT0003041 . Electronic supplementary material The online version of this article (10.1186/s12891-019-2703-0) contains supplementary material, which is available to authorized users.

Knee Extensor Strength Measurement in Patients With Limited Physical Activity Using a Supine Dynamometer Anchoring Frame

“…The angle of 35° was chosen keeping in mind previous study results, which reported that high-level surface electromyography activity was observed when the knee joint was flexed at 35° [ 14 ]. Studies measuring knee extensor strength with the knee joint flexed at 35° in the HHD test showed good reliability [ 9 , 13 , 15 ]. Four U-shaped rings were placed on the corners of the frame to connect the belts for fixing the device to the bed.…”

“…Four U-shaped rings were placed on the corners of the frame to connect the belts for fixing the device to the bed. The thighs of the participants can be fixed using a Velcro strap to minimize hip flexion movement [ 13 ].…”

“…Isometric knee extension strength was assessed with a microFET IITM (Hoggan Health Industries, Draper, UT, USA), which is a battery-operated load cell system with a digital reading of peak force ranging from 12.1 N to 1,334.5 N, in 0.4 N increments. The HHD was placed 5 cm above the upper margin of the lateral malleolus [ 13 ].…”

“…Before the measurement, the subjects performed knee extension of the dominant leg several times to become familiar with the device. The measurements consisted of three total sessions consisting of three 5-second maximal isometric contractions of the dominant knee extensors, in each trial [ 13 ].…”

“…Recently, Sung et al [ 13 ] suggested the use of a portable dynamometer anchoring system that can measure knee extensor strength in the supine position, and confirmed its reliability and validity in 39 healthy people. This system can be appropriately applied to cases where it is difficult to move the patients to the laboratory or for patients who have difficulty maintaining a sitting position during the test, since the system can measure strength in the supine position.…”