Synergistic Relationship Between Muscle Thickness, Muscular Strength, and Functional Fitness After Resistance Training in Older Women.

Stavinski, N, Cavazzotto, TG, Carneiro, MAS, Kunevaliki, G, Francsuel, J, Costa, B, Kassiano, W, Tricoli, I, Castro-E-Souza, P, Prado, A, Cyrino, LT, Rodrigues, RJ, Silva, DRP, Cavaglieri, CR, Silva, AM, Sardinha, LB, and Cyrino, ES. Synergistic relationship between muscle thickness, muscular strength, and functional fitness after resistance training in older women. J Strength Cond Res XX(X): 000-000, 2025-This study examined the synergistic relationship between changes in muscle thickness (MT) and muscular strength and functional fitness after a resistance training (RT) program in older women. Sixty physically independent women (68.8 ± 5.9 years) participated in a 24-week RT program. The MT, muscular strength, and functional fitness were analyzed at baseline and after 12 and 24 weeks. The whole-body RT program was conducted in 3 weekly sessions (8 exercises, 3 sets of 8-15 repetitions). The repeated measures correlation analysis revealed significant correlations between MT and muscular strength (rrm = 0.51 to 0.78; p < 0.05) and functional fitness tests (rrm = 0.27 to 0.45; p < 0.05). Further analysis using repeated measures regression revealed significant associations between MT and muscular strength (R2 = 0.16 to 0.54; p < 0.05) and functional fitness tests (R2 = 0.10 to 0.32; p < 0.05). Furthermore, repeated measures mediation showed that 7.4 and 19.8% of the relationship between RT engagement and 1 repetition maximum (1RM) leg extension and 1RM preacher curl, respectively, was attributed to increases in MT. However, MT did not mediate the relationship between RT and 1RM chest press, handgrip strength, 4-m gait speed, timed-up-and-go, 5-repetition sit-to-stand (5STS), 30-second sit-to-stand, and 6-minute walk. Changes in MT induced by RT may account for a significant portion of the changes in muscular strength, but not in functional fitness.