Validity and Reliability of Maximal Strength Assessment of Knee Flexors and Extensors Using Elastic Bands

In the field of sport rehabilitation, an easy, valid and reliable assessment of maximal strength is critical for an efficient muscular rehabilitation. Traditionally, it is performed on fitness equipments, which are not always available in the field. Thera-Band® has developed elastic bands with different resistances depending on the color of the band and on the percentage of stretch of this last. This could allow testing maximal strength. This study aimed to determine validity and reliability of maximal strength assessment of knee flexors and extensors using elastic bands. A total of 22 healthy people (31.3 ± 7.0 yrs, 175.5 ± 8.5 cm, 70.7 ± 12.9 kg) participated this study. Participants performed two maximal strength assessments, separated by seven days, of knee flexors and extensors using elastic bands. After the second trial, a maximal concentric isokinetic test at 60°·s-1 was performed. Correlations between one repetition maximum (1-RM) using elastic bands and peak torque (PT) on isokinetic dynamometer were used to determine the validity of the proposed method, while ICC, CV and SEM were employed to determine the reliability between first and second trials. The validity of the proposed method was found to be very high (r = .93 for both knee flexors and extensors). The relative reliability was found to be very high (ICC = .98 and .99 for knee flexors and extensors, respectively), while absolute reliability was also very satisfying (CV = 3.44% and 2.33%; SEM = 1.70 kg and 2.16 kg for knee flexors and extensors, respectively).

The study found Thera-Band® to be a valid and reliable substitute for the use of fitness equipments to test maximal strength of knee flexors and extensors in healthy subjects. The ease of use, accessibility and low cost of elastic bands should enable regular assessment during the rehabilitation process.

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