Relationship of Phase Angle, Echo Intensity, and Muscle Thickness with Isokinetic Knee Extensor Strength and Associated Motor Functions in Young Adults

Background: There is no comprehensive report on quadriceps femoris muscle parameters’ association with isokinetic knee extensor strength, and no study has comprehensively clarified the relationship with motor function. To investigate the relation of isokinetic knee extensor strength and motor functions with phase angle, muscle echo intensity, and muscle thickness, to find alternative methods for knee extensor strength assessment. Methods: This cross-sectional study evaluated the associations between phase angle (PA) (measured using bioelectrical impedance analysis) , muscle echo intensity (EI), and muscle thickness (MT) (measured using ultrasound) and isokinetic knee extensor strength (measured as maximum torque at 60 degree/s using an isokinetic dynamometer), and motor functions evaluated by gait speed (usual and maximum), five chair stands time, and stand up score. Results: The study comprised of 33 young healthy adults (12 males and 21 females; mean age, 22.2 years). Both sexes showed a significant correlation between isokinetic knee extensor strength and PA (males, r = 0.65, females, r = 0.54), muscle EI (males, r = -0.53, females, r = -0.54), and MT (males, r = 0.34, females, r = 0.38). In addition, a significant correlation was found between PA and maximum gait speed (males, r = 0.64, females, r = 0.44), five chair stands time (males, r = -0.69, females, r = -0.62), and stand up score (females, r = 0.45), and between muscle EI and maximum gait speed (males, r = -0.34, females, r = -0.42), five chair stands time (males, r = 0.37, females, r = 0.33), and stand up score (females, r = -0.30). Conclusions: The study suggests the potential of phase angle and muscle echo intensity as alternative assessment methods for isokinetic knee extensor strength.