Background: Grip strength is the gold standard for the assessment of muscle strength. The current methods of measuring grip strength can only reflect the overall function of the muscle group, not an actual muscle lesion or the cause of the lesion. Virtual touch tissue imaging and quantification (VTIQ) technology can provide a representation of muscle properties and quantify alterations in muscle mechanics through measurements of the mean shear wave velocities of the muscle group at a designated location.
Methods: A total of 70 healthy middle-aged females were included. The maximum grip strength and thickness of the forearm and hand muscle under relaxed conditions were measured, and the sum of the muscle thicknesses was calculated. VTIQ was used to measure the shear wave velocity (Vs) of the flexor pollicis longus, flexor digitorum profundus and flexor digitorum superficialis. Intra-group correlation coefficient (ICC) was used to evaluate the test-retest reliability of the grip strength and Vs values, and the correlation of the thickness and Vs of each forearm and hand muscle with grip strength was calculated.
Results: (I) The hand-held dynamometer and the VTIQ technology have good test-retest reliability in muscle evaluation (all P<0.001). (II) The muscle thickness of the lumbricals did not exhibit a significant correlation with grip strength (P>0.05). The forearm radial MT (muscle thickness), forearm ulna MT, summation of four MTs, and interosseous MT showed positive correlations with grip strength (r=0.445, 0.824, 0.722, and 0.359, all P<0.05). The Vs values of the flexor pollicis longus, flexor digitorum superficialis, and flexor digitorum profundus showed negative correlations with grip strength (r=-0.962, -0.919, and -0.456, all P<0.01). Stepwise linear regression revealed that forearm radial, ulnar muscle thickness, and flexor digitorum superficialis Vs can be utilized concurrently to predict 90.7% of the variability of grip strength (R2=0.907).
Conclusions: The structure and stiffness values of skeletal muscles obtained through conventional ultrasound coupled with VTIQ showed good correlations with the variation in grip strength and can evaluate the changes of muscle strength.
Keywords: Grip strength; elastography; muscle strength; ultrasound.