Validity of using elastic bands to measure knee extension strength in older adults

Background and objectives: Maximal strength assessment of knee extensors in older adults using elastic resistance bands have rarely been addressed even though resistance training using elastic bands have shown large effects on muscle strength in this group of people. We therefore aim to determine the validity of maximal knee extension strength assessment using elastic resistance bands in older women and men. Methods: Twenty-four participants (12 women and 12 men; 61.8 ± 6.0 years; 173.5 ± 10.2 cm; 71.9 ± 15.7 kg) were included. To assess maximal knee extension strength, participants performed one-repetition maximum testing of concentric knee extension using elastic resistance bands as well as a maximal concentric knee extension isokinetic test at 60°/s using a stationary isokinetic dynamometer. Concurrent validity of the two measurement techniques were assed using intraclass correlation coefficient (ICC2.1), Pearson correlations (R), concordance correlations (Rc) and by determining variations on an individual level using 95% limits of agreement (LoA) with isokinetic dynamometry measurement as the reference standard. Results: Validity analysis showed good to excellent agreement and relationships but wide 95% LoA between elastic one-repetition maximum and isokinetic peak torque for all participants (ICC = 0.88; R = 0.90; Rc = 0.85, LoA = 10.5 kg), for women (ICC = 0.67; R = 0.77; Rc = .62, LoA = 7.7 kg) and for men (ICC = 0.80; R = 0.85;Rc = 0.78, LoA = 13.1 kg), respectively. Conclusion: One-repetition maximum testing using elastic resistance bands provides valid measurements of maximal knee extension strength in older women and men but with wide variations on an individual level.