Skeletal Muscle Compliance and Echogenicity in Resistance-Trained and Nontrained Women

Abstract

Mongold, SJ, Ricci, AW, Hahn, ME, and Callahan, DM. Skeletal muscle compliance and echogenicity in resistance-trained and nontrained women. J Strength Cond Res 38(4): 671-680, 2024-Noninvasive assessment of muscle mechanical properties in clinical and performance settings tends to rely on manual palpation and emphasizes examination of musculotendinous stiffness. However, measurement standards are highly subjective. The purpose of the study was to compare musculotendinous stiffness in adult women with varying resistance training history while exploring the use of multiple tissue compliance measures. We identified relationships between tissue stiffness and morphology, and tested the hypothesis that combining objective measures of morphology and stiffness would better predict indices of contractile performance. Resistance-trained (RT) women (n = 11) and nontrained (NT) women (n = 10) participated in the study. Muscle echogenicity and morphology were measured using B-mode ultrasonography (US). Vastus lateralis (VL) and patellar tendon (PT) stiffness were measured using digital palpation and US across submaximal isometric contractions. Muscle function was evaluated during maximal voluntary isometric contraction (MVIC) of the knee extensors (KEs). Resistance trained had significantly greater PT stiffness and reduced echogenicity (p < 0.01). Resistance trained also had greater strength per body mass (p < 0.05). Muscle echogenicity was strongly associated with strength and rate of torque development (RTD). Patellar tendon passive stiffness was associated with RTD normalized to MVIC (RTDrel; r = 0.44, p < 0.05). Patellar tendon stiffness was greater in RT young women. No predictive models of muscle function incorporated both stiffness and echogenicity. Because RTDrel is a clinically relevant measure of rehabilitation in athletes and can be predicted by digital palpation, this might represent a practical and objective measure in settings where RTD may not be easy to measure directly.

Figure 1.

Tissue tracking. Aponeurosis displacement was calculated by taking the average displacement of a segment’s end points from precontraction to midcontraction (left column). Dark gray segment signifies user-selected portion of aponeurosis (top left). White segment represents the same segment as it displaces proximally during contraction. PT elongation was calculated by taking the difference in segment lengths, as defined by the distal edge of the patella to the hypoechoic band, across images from precontraction to midcontraction (right column). PT = patellar tendon.

Figure 2.

Tissue stiffness as assessed using the MyotonPro and US at the patellar tendon (PT). Trained women demonstrated significantly greater stiffness. * indicates p < 0.05, ** indicates p < 0.01. US = ultrasonography.

Figure 3.

Composition differences and relation to muscle function. Groups were significantly different in corrected echogenicity (A). Corrected echogenicity was strongly related to muscle strength normalized to body mass (B). * indicates p < 0.01.

Figure 4.

Associations between voluntary PT force and stiffness measured using myotonography. The slope of the relationship between PT force and MyotonPro stiffness was not significant (p = 0.1) in nontrained (NT) subjects. This relationship was significant in resistance-trained subjects (RT; p = 0.04). PT = patellar tendon.

Figure 5.

Associations relevant to passive stiffness measurements. Scatterplot of passive stiffness at the VL vs. SAT at VL (A), passive stiffness at the PT vs. SAT at the PT (B), SAT at the PT vs. RTD_rel (C), and passive stiffness at the PT vs. RTD_rel (D). SAT = subcutaneous adipose thickness; VL = vastus lateralis; PT = patellar tendon; RTD = rate of torque development.