Synergistic Relationship between Muscle Thickness and Cellular Health after Resistance Training in Older Women

This study investigated the relationship between muscle thickness and raw and derived bioelectrical impedance analysis (BIA) parameters following 12 wk of resistance training (RT) in older women.

Fifty-five older women were assigned to a control group ( n = 31) or an RT group ( n = 24). Muscle thickness was assessed using B-mode ultrasound, while BIA parameters, including reactance (Xc), resistance (R), phase angle (PhA), intracellular water, extracellular water (ECW), and total body water, were measured at 50 kHz. Total and appendicular lean soft tissue and fat mass were evaluated via dual-energy X-ray absorptiometry.

Muscle thickness and total and appendicular lean soft tissue increased in the RT group (2.9%-6.2%; P < 0.001), whereas muscle thickness decreased in the control group (-4.1%; P < 0.001). Xc, PhA, and ECW also increased in the RT group (1.6%-5.8%; P ≤ 0.002) but decreased in the control group (-1.1% to -5.8%; P ≤ 0.022). In the RT group, muscle thickness was positively correlated with Xc, PhA, total body water, and ECW ( rrm = 0.40-0.52; P ≤ 0.023), whereas in the control group, muscle thickness correlated only with Xc, R, and PhA ( rrm = 0.43-0.46; P ≤ 0.015). Linear mixed models showed that muscle thickness was associated with all raw and derived BIA parameters in the RT group but only with PhA in the control group.

Our findings suggest that increases in muscle thickness resulting from a 12-wk RT program are synergistically associated with changes in both raw and derived BIA parameters, which may play a crucial role in enhancing cellular health in older women.