Limb Muscle Quality and Quantity in Elderly Adults with Dynapenia but Not Sarcopenia: An Ultrasound Imaging Study

Background: Dynapenia is prevalent in people with reduced skeletal muscle mass, i.e. sarcopenia, but a certain population develops muscle strength loss despite having normal skeletal muscle volume. To date, studies investigating muscle quality and quantity in groups with dynapenia but not sarcopenia are limited.

Methods: Echogenicity and thickness of the biceps brachii, triceps brachii, rectus femoris, and medial gastrocnemius muscles were measured using high-resolution ultrasonography in 140 community-dwelling elderly adults. Participants with decreased handgrip strength but normal muscular volume were diagnosed as having dynapenia without sarcopenia. A multivariate regression model was used to analyze the association between dynapenia and ultrasound indicators of the sampled muscle expressed as odds ratio (OR) and 95% confidence interval (CI).

Results: A total of 140 participants were recruited for the study, 12.6% (n = 18) of whom had dynapenia. The dynapenia group had a higher mean age, higher proportion of women, slower fast gait speed, reduced handgrip strength, and decreased thicknesses of the biceps brachii, rectus femoris, and medial gastrocnemius muscles. On multivariate logistic regression analysis, dynapenia was associated with older age (OR, 1.18; 95% CI, 1.05 to 1.33), higher body mass index (OR, 1.28; 95% CI, 1.05 to 1.64), and decreased thicknesses of the rectus femoris (OR, 0.01; 95% CI, <0.01 to 0.24) and medial gastrocnemius muscles (OR, 0.03; 95% CI, <0.01 to 0.61).

Conclusion: Dynapenia without sarcopenia is associated with decreased thicknesses of the rectus femoris and medial gastrocnemius muscles, an association that remains significant after adjustment for demographics, body composition, and physical performance. Ultrasound measurements of lower-limb muscle thickness can be considered an auxiliary criterion for evaluating dynapenia.