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.

Temporally stable beta sensorimotor oscillations and corticomuscular coupling underlie force steadiness.

As humans, we seamlessly hold objects in our hands, and may even lose consciousness of these objects. This phenomenon raises the unsettled question of the involvement of the cerebral cortex, the core area for voluntary motor control, in dynamically maintaining steady muscle force. To address this issue, we measured magnetoencephalographic brain activity from healthy adults who maintained a steady pinch grip. Using a novel analysis approach, we uncovered fine-grained temporal modulations in the beta sensorimotor brain rhythm and its coupling with muscle activity, with respect to several aspects of muscle force (rate of increase/decrease or plateauing high/low). These modulations preceded changes in force features by ∼40 ms and possessed behavioral relevance, as less salient or absent modulation predicted a more stable force output. These findings have consequences for the existing theories regarding the functional role of cortico-muscular coupling, and suggest that steady muscle contractions are characterized by a stable rather than fluttering involvement of the sensorimotor cortex.

Afferents to Action: Cortical Proprioceptive Processing Assessed with Corticokinematic Coherence Specifically Relates to Gross Motor Skills.

Voluntary motor control is thought to be predicated on the ability to efficiently integrate and process somatosensory afferent information. However, current approaches in the field of motor control have not factored in objective markers of how the brain tracks incoming somatosensory information. Here, we asked whether motor performance relates to such markers obtained with an analysis of the coupling between peripheral kinematics and cortical oscillations during continuous movements, best known as corticokinematic coherence (CKC). Motor performance was evaluated by measuring both gross and fine motor skills using the Box and Blocks Test (BBT) and the Purdue Pegboard Test (PPT), respectively, and with a biomechanics measure of coordination. A total of 61 participants completed the BBT, while equipped with electroencephalography and electromyography, and the PPT. We evaluated CKC, from the signals collected during the BBT, as the coherence between movement rhythmicity and brain activity, and coordination as the cross-correlation between muscle activity. CKC at movements' first harmonic was positively associated with BBT scores (r = 0.41, p = 0.001), and alone showed no relationship with PPT scores (r = 0.07, p = 0.60), but in synergy with BBT scores, participants with lower PPT scores had higher CKC than expected based on their BBT score. Coordination was not associated with motor performance or CKC (p > 0.05). These findings demonstrate that cortical somatosensory processing in the form of strengthened brain-peripheral coupling is specifically associated with better gross motor skills and thus may be considered as a valuable addition to classical tests of proprioception acuity.