Background/Purpose Muscle power (MP) plays an important role in daily activities that require force generated at fast speeds such as climbing stairs. MP is decreased in individuals with arthritis and its contribution to disability has been suggested to be above that of muscle weakness. Yet, there is no consensus on testing parameters such as angular speed and muscle contraction curve to assess MP using isokinetic dynamometers. The purpose of this study was to investigate testing parameters used to assess quadriceps MP in subjects with arthritis. Aim 1 tested the associations of angular speed (or slope of angular speeds) and muscle contraction curve with a well-accepted performance-based measure of MP – the stair climbing test (SCT). Aim 2 investigated whether MP explains variability in SCT beyond that of demographic variables related to muscle performance and muscle strength.
Methods Adults diagnosed with rheumatoid arthritis were invited to participate. This cross-sectional study used an isokinetic dynamometer to measure quadriceps maximal voluntary isometric contraction (MVIC) and MP. MP was measured using four angular speeds of contraction (240, 180, 120, and 60 degrees per second). Then, values of MP were retrieved from the dynamometer using 3 methods: 1) MP of the whole muscle contraction curve (maximum knee flexion to knee extension); 2) MP of partial curve up to peak torque (maximum knee flexion to peak torque), and 3) MP of partial curve deleting 10° of acceleration and deceleration from whole curve. We also calculated power slopes using MP of the 4 speeds for each curve method. SCT was measured in seconds as the time to go up 11 steps. Bivariate correlations were calculated to determine the associations between SCT and MP at the 4 angular speeds and power slope for each curve method. Separate hierarchical regression models were built to determine the contribution of each method to measure MP on SCT after controlling for age, gender, BMI, and MVIC.
Results Sixty one subjects participated (age 59 ± 1 years, 82% female, BMI 31 ± 0.9 kg/m²). All bivariate correlations coefficients between MP and SCT were significant and ranged from -.35 to -.54 (p < 0.001). Hierarchical regression analyses demonstrated that age, gender, and BMI explained 46% of variability in SCT. After adjusting for these variables, MP explained significant variability in SCT regardless of the angular speed or curve method used (7% to 17%). In separate regression models, after adjusting for demographics, MVIC was added and explained additional 15% of variability. Then, MP measures were added to the models. The only variable that contributed significantly to SCT in this model was the MP slope measured by the curve method that excluded acceleration/deceleration (Beta -.326; p=0.027).
Conclusion The contribution of MP to SCT was beyond demographics and muscle strength only when measured as MP slope (combining all angular speeds) and used the curve method that discarded acceleration/deceleration. When measuring MP, utilization of MP slope rather than a single speed of contraction and carefully selection of the curve method are encouraged.
Disclosure:
M. B. Catelani,
None;
S. S. Khoja,
None;
G. J. Almeida,
None;
S. R. Piva,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/investigation-of-parameters-used-to-test-quadriceps-muscle-power-using-isokinetic-dynamometer-in-arthritis/